The  photos show  a simple device that can be made to use a threaded rod to adjust the A/C belt tension.

 One end is bolted to the A/C unit and a 3/8" diameter threaded rod with a short 90 degree bend that sticks into a hole on the A/C adjustment bracket.

 I made it by drilling the threads out of a 2" long "coupling" nut and welding a short tab with a 3/8" diameter hole drilled in it.  Only requires removing one bolt to attach the device.  No drilling or modifications required on the vehicle.  Sure beats using a pry bar to tension the A/C belt.ChuckA


Here is some information about dash a/c vent repairs.  Be sure to read the notes below the pictures.
J. Harper

What is the part # for the Receiver / Dryer / Dehydrator for the A/C system?
NAPA Part #208508. Cost $36.10

  Solaire Furnace Replaced with a Suburban SH-30 or SH-35

Mounting without Fiberglass Repairs
by Wally Anderson (SH) http://www.gmcmhphotos.com/photos/showphoto.php?photo=16086
by Bill Gagnier(SF) http://www.gmcmhphotos.com/photos/showgallery.php?cat=4654
Suburban SH specifications http://www.rvcomfort.com/suburban/products/furnaces/sh.php
Surburban SF specifications http://www.rvcomfort.com/suburban/products/furnaces/sf.php

  I have an SH-35 Suburban installed. It can be used for inside or outside access and costs less if you don't buy the ouside access door. The major difference between the SF and SH models is that the SH is a little taller and is supposed to be quieter as the blower is larger in diameter and turns slower.

I was able to mount it (SH-35)on a slant and use the rear Solaire vent hole after enlarging it. The front Solaire vent is still on there but blocked off and not used. That way I figured on not having a hole to patch and paint. The SH and SF are wider than the Solaire and rectangular in shape. It won't fit out the cabinet door and would have to go out towards the front after removing the couch. I'm thinking of modifying the cabinet so it would fit out but haven't yet.

 Most have installed the NT 30 which is square in profile closer to the Solaire. Arch has installed an NT 30 and his album is here:
Wally Anderson

A lot of us have done this for fresh air,   works well in the aridCalifornia
My version.  I used 4" vents.  3" vents might be enough.  I've got LOTS of air.

The wind wings work, too.  Much easier to install.  Also lots noisier at speed.  The floor vents are almost silent.Kelvin
You might want to consider another alternative.

This one does not require cutting any metal because it comes up through thefloor instead of the firewall.  Also simplified controls as these can be turned on by rotating the little knob on the grill instead of having to hookup more complicated controls.  I have tweeked my installation a little. Iremoved the dryer vent part and repositioned the driver's side scoop becauseit was getting hit by the steering linkage but the photos will give you theconcept.  Would like to update my pictures but the coach is in the storage lot - Bob

Dripping Roof AC

If your roof A/C happens to be leaking condensation inside your coach, like mine and a couple of other GMCer's use to, let me save you several months of frustration.  Go inside your coach and
remove the a/c cover.  Now remove the four bolts that go through the roof holding the exterior part of the a/c to the roof.  Some a/c's only have three, two corners and one center rear.  With these bolts removed, you will now have access to the 4 inch air duct.  The two sheet metal screws holding the air duct to the bottom of the exterior part of the roof a/c are the culprits.  The OEM seal has gone bad.  Remove any left over OEM sealant, clean and dry the screws and holes.  Apply new caulking to the screws, holes, air duct lip and re-install.  You will be surprised how much water can come through those two little holes even with the sheet metal screws in them.  We found this to be the problem on Penguin and Brisk Air roof a/c's.Jim Bolick

There are no O rings in it.  There is a rotary disk made of plastic and a rubber disk with grooves in it that direct the vacuum to the various servos (defrost, heat, AC, etc.).  One of the most common problems is that there is a small plastic pin with two prongs that holds it together and there is a flex plate spring that puts tension on the assemble to seal it.  The pin gets brittle and breaks and then the unit leaks vacuum.  Alex Sirum makes a metal replacement pin.

Your problem is probably a broken pin.

If you take it apart I have found that you can take some very fine wet or dry sandpaper or crocus cloth and polish the face of the rubber disk and around the plastic disk and when you reassemble it use some silicone grease (CAUTION: to those with O2 probes DON'T use silicone grease as it will be drawn into the intake manifold and will quickly ruin the O2 probe).  If you have an O2 probe just use some light oil to lubricate it.
Emery Stora
77 Kingsley
Santa Fe, NM

Which AC do I have?

In about mid-year 1977 and for all 1978 models they made some changes.  I wasn't looking at the book and was somehow thinking that it was the second generation but after looking at the 1975-76 Maintenance manual I see that they called it Type I and Type II in those model years.  If one were to look at the control panel you can tell which model you have.  The only difference in the control panel appearance from Type I to Type II is that the fan switch on the left side has an OFF position for the type I and it says LO for the Type II.  Some of the 1977 models have the Type II but in mid year they did another upgrade with quite a few changes.  The appearance of the control panel has the same LO at the bottom position of the Fan switch but the AIR COND section shows MAX on the left and NORM in the center.

The other changes made to the system in 77-78 are:
1.  Increased refrigerant charge -- 3-3/4 pounds instead of 3-1/2 pounds.
2.  New A/C heater control head and new control panel components.
3.  New A/C plenum and revised duct system.
4.  New vacuum system.
5.  Revised heater and evaporator assembly.
6.  Baffles added at condenser and heater/evaporator housing.
7.  Addition of time delay relay in blower circuit wirings.
8.  Externally equalized thermal expansion valve.
9.  Smaller diameter high pressure service fitting on late 77 model vehicles and on all 1978 model vehicles - fitting size is 3/8"-24.
10.  Revised compressor mounting.
11.  Inverted vacuum tank mounting.
12.  Revised Discharging, Evacuating and Charging Procedures.

As I said previously, not all 1977 models have these changes.  The earlier production have the Type II.  My 1977 was manufactured in 11/76 and it does have this newer design. Emery Stora


CLASCO AC conversion Kit
Original configuration Article  Air Conditioning "Separating Hot from Cold" by Zay Brand.



LATE 73 - 74

74 - 76
DEC 75
76 - 77

LATE  76 - 78
NOV 76
III  ?

Conversion to Duracool

    Duracool is a packaged propane butane mix that cools with greater efficiency than R12, and cost about $20 to fill your GMC. It is illegal in some states. I am testing it in my GMC, which ran my own "home brew" of propane and isobutane (55 to 45%) that worked better than R12 but was a pain to refill. Also my Head pressures were a little high (250 psi on a hot day). Now I'm running 40 to 140 low to high. If you don't know what I'm talking about that's ok. Here's what's important.

    My system leaks. I don't want to fix it as the leak is very slow and when I redo the whole coach I'll replace everything. Until then what can I do? I ran my own mix, but I wanted to try a commercial hydrocarbon mix. Duracool seams to work much better than R134a, and possibly better than R12. I won't know until further testing. But, this stuff is cheap, $5.50 for 6 oz, which equals 15 ozs of R12. That means about $20 to fill your GMC.Mark A

How to Recharge your GMC with Hydrocarbon refrigerants

Here are some bits of information that we learned at Osoyoos: (5/5/5)
1 AC technicians do not like to use 134, it is harmful to their health.
2 You do not need a vacuum pump to charge with Hydrocarbon refrigerants like DuraCool (Propane).
3 In fact they work better if you do not pull a vacuum.
4 Propane will mix with whatever you have in your system. There’s nothing to change.
5 Recover the existing refrigerant (most of our systems are already empty).
6 Add 3 cans of DuraCool
7 Use Glacier Gold if you have a leak, every can has a dye for leak detection.
8 Run the compressor, and measure the low side with your tire gauge.
9 You should have 30 lb of pressure. If it’s too high let some out, a little low will be ok.
It should be 20-25 depending on the ambient temperature and measured at. 1500 rpm. - emery 2012
10 Put on the 134 adapter connections, and the system is legal.
11 Mark the system as filled with DuraCool or Propane.
12 You are done, no gages, no pump, no changes.
13 Propane is more efficient. Your compressor will use 40% less horsepower.
14 The head pressure is lower with Propane, the compressor will last longer.
15 It will cost you $30 for the Propane and taper hose.
16 Propane has a higher auto ignition temperature than 134. (Propane still lights more easily)
17 Propane leaks less than R12.
It has never been easier to do your own AC work. It is interesting to note that there is also a hydrocarbon mixture that works on a home or coach AC to replace the R-22 with the more efficient refrigerant.
Note: The EPA has issues with Hydrocarbon refrigerants. You should read this link and make your own decision: http://www.epa.gov/ozone/snap/refrigerants/hc-12a.html#q9
The above information and more technical detail are available on these web pages:



 I bought a case of 12 cans and several of the fittings from them last year. I was just over there a couple of days ago, and they still carry it. Prices are competitive.

RIVERSIDE, CA  92501-1126
Phone: 951-369-9741  Tmaki

Called Chet at Shamrock Consultants in Fresno Ca.
Shamrock is the out let for Duracool 12a in California or as Ken would say Kalifornia.
His phone number 559 255 9413

IDEAL COOLANT SOLUTIONS       Serving Washington and Oregon

WEBSITE        http://www.idealcoolantsolutions.com
Craig Piguet - Oregon Sales
12530 SE Oatfield Rd. #2
Milwaukie, OR 97222
Email                cpiguet@idealcoolantsolutions.com
Telephone         503-419-6392

Peter Strait - Washington Sales
Prairie Rose Lane
Lyle, WA 9863526   
Email                pstrait@idealcoolantsolutions.com
Telephone        360-518-4142

Flammability OF HC refrigerants

Flammability is not much of an issue compared to the use of gasoline in your engine compartment. 

For a number of years now there have been many messages posted on the GMCnet about the use of hydrocarbon refrigerants to replace R-12 or R-134a.  Products such as Duracool and HC-12a, which are both mixtures of Propane and Iso-butane, are currently being used by many GMCers.

 I felt it might be good to examine the reported track record of hydrocarbon refrigerants.

Major conversion of car air conditioners from fluorocarbon to hydrocarbon refrigerant commenced  in the USA in Idaho during 1992.  I have been looking on the Internet for statistics and find that today over 10 million car air conditioners worldwide have been  converted, about half of these in North America, and over 30 million user years have accumulated.   Almost all of these have been drop-in conversions usually costing less than US$50.  Indonesia,  Korea, Philippines, China, Canada, Australia, Japan and other countries also have many systems with drop-in HC charges.    In spite of this, there have been no reported fires, explosions or injuries to occupants caused by the flammability  of hydrocarbon refrigerant in car air conditioners.  Many cars with hydrocarbon refrigerant have  had frontal collisions which punctured the condenser.  Arthur D. Little, the well known consulting firm, estimated the frequency of  the refrigerant catching fire from this common accident as once in ten thousand user years, so over  3,000 such fires should have occurred worldwide;  if this had happened it would have been big news and widely reported. But even so,  no such fires have been reported.  There are reports of such accidents with the refrigerant not  catching fire.    HC refrigerants have a condenser pressure 10% lower than HFC-134a, making catastrophic leaks  many times less frequent.  HC REFRIGERANT IS ONLY FLAMMABLE BETWEEN 2 AND 10% VOLUME

CONCENTRATION IN AIR.  It is non-flammable inside the refrigerant circuit where the concentration is  always above 10%.  HC refrigerants have a high leak and low flame velocity so an ignited leak tends to blow itself out.  HC refrigerants have a lower density so the charged mass is only one fourth  of  HFC 134a.  When this small charge leaks from the evaporator into the passenger cabin, air leaks  keep it non-flammable by preventing the concentration from 
exceeding 2%.  HC refrigerants also have an  odorant added to help prevent accidents.

Has any of the GMCnetters actually seen or even heard of an actual fire?

I feel it is a matter of personal choice as to one's aversion to risk.  1 in 50 million might be acceptable odds to some but might be unacceptable to others.  I personally feel that 0.00000002 is sufficiently close to zero.  So, the benefits of using HC refrigeration in my GMC far outweigh any fire risk in my mind.  You 
have to make up your own mind on this, though.

Europe is currently undergoing a transition away from the use of R-134a due to its potential of adding to global warming.  Many European countries signed the Kyoto Protocol (the USA did not).  Replacements under consideration are hydrocarbon products for existing systems and a newly designed system using CO2 as the refrigerant.  However, existing systems cannot use CO2.  It will require a different heat exchanger and re-engineering of every component.  The CO2 systems will have pressures in the range of 1500 psi to 2000 psi or more.  This is about 10 times the pressure found in a conventional AC system.  Mercedes has indicated that they may have a CO2 system by 2005.

The advantage of using hydrocarbons instead of HFC-134a is that the greenhouse effect of  refrigerant leaks could be eliminated completely. The only argument against HC blend refrigerants, the flammability issue, has proven to be a non-argument. Plus, the international community, as well as Greenpeace and the UN, are advocating the use of HC blend refrigerants in all applications. This in response to the Kyoto agreement which scheduled the phase-out of greenhouse gases as 
the Montreal Protocol scheduled the phase-out of ozone-depleting chemicals. >>>>>

I am not taking a political stand on these issues, I am just reporting information that I have reviewed. Emery Stora (5/28/06)

Comparison of  refrigerants

FR-12 or Freeze - 12

you might run into someone who wants to replace your R12 with "FR-12" or "Freeze-12" or "Frigc".  These three (and several others) are simply 134a with an additive that makes it slightly less violently incompatible with 500sus mineral oil.  Long term you could have problems with Freeze 12.

They are still basically R134a and not in the same class as Duracool which is totally compatible with both a R12 and a R134a system  EmeryS

R406A (Tradename Autofrost) does everything > you claim for Duracool, but  IS legal.   Once again, why fool with an inferior, illegal product like  Duracool, when there are far better alternatives?

    R406A is not a Hydrocarbon refrigerants, and is basically nonflammable. Good stuff there, if you are worried about flammability then R406A is a good refrigerant to use.

Now here are a few problems with R406A:
First, this product requires barrier hoses, so ALL AC hoses must be replaced. Duracool can use the old original hoses.

R406A can have compatibility problems with the compressor seal. Your compressor seal must be Neoprene, or it will fail, Duracool has no compatibility problems.

R406A must be recovered, ie; must be sucked out of your system by a licensed AC repair shop, (good luck, the vast majority of AC shops won't dare contaminate their equipment with it, you have to find a shop pushing R406A). You can dump it in the atmosphere but that's illegal, and

R406A is only 95% non-corrosive to the Ozone layer, Duracool is 100%, and though they tell you to recover it, the backyard amateur owner mechanic can dump it, it has NO regulated HCFC's.

R406A cannot be used with ester (PAO) or PAG oils, if you system has been converted to R134 then it almost certainly contains ester oils and must be flushed, especially the compressor.

R406A contains some very small molecules, and if there are any leaks in your system, they will allow the "lighter" elements of R406A to dissapear,(why it needs barrier hoses) and your system will become inefficient and ultimatily lose cooling ability.

Other than that, R406A will work great, and if you rebuild your system and cover these problems it is an excellent, fire safe refrigerant. I use duracool because I'm cheap and it's cheap and will work great in an old leaky system. It costs be about $30 to charge my system, and so far 2 years down the road it's still working great.
In all my years of working as an auto mechanic, I've not seen a car with the peculiar state of damage that would allow the evaporator to leak without massive leakage under the hood. Remember, the amount we are talking here is ounces, there is very little of this stuff in the AC system. I carry a gallon of camping fuel in the coach for our camp stove, that is far more dangerous that my AC. And yes, that needs to be stored outside.     One last thing, go to the Duracool website and read up on the legalisms, you might be surprised.  I understand that some insist on this, and others insist on that. I insist on nothing, except tolerance for other viewpoints.
Mark A

After pumping the system down and making sure that this time there were no leaks, I took the plunge. The directions say that you fill the system by volume and not by amount. That means you need gages to monitor the low side while adding the DuraCool and then you are suppose to bring the pressure up to 35lbs.  This is when they say it is full.

There was a chart at duracool.com that shows the equivalences between DuraCool and R12. This shows 6 oz of DuraCool equals 17 oz of R12. Our systems use roughly 3.5 lb. of R12, so this converted to just a little over 3 cans of DuraCool. The  kit that I bought from DuraCool had 3 6 oz cans in them. I went ahead and put 2 cans in quickly, and the pressure came up to around 10lbs. I then slowly added the 3rd can, and watched the pressure come up to the 35lbs.

I let the system run for 30 minutes or so (at about 1000 rpm), and the pressure stayed at the 35lbs. So, I didn't add anymore. It's blowing real cool, and we are excited about having AC for the trip this weekend. All in all I'm happy with it. Now I need to make the recirc mod, cause right now all of the inlet air is coming from the hot engine compartment.

The DuraCool kit cost me $37 (3 6 oz cans plus the hose to puncture the can and attach it to the R12 shrader valve). 5 12 oz cans of R12 would have cost me $100-$150, and that would be if I could get anyone to sell it to me.

Conversion To R134a

 R134a does not require barrier hoses, only refrigerants containing HCFC 22.     The original oil used in R12 systems is not soluble in R134a so a different oil must be used. If Ester Oil is used, no special "O" rings are needed, and the system does not have to be flushed.

The receiver dryer should be replaced to provide adequate water absorption, and because it is often impossible to drain the old oil from it. The compressor's oil should be drained. The expansion tube (if any) should be cleaned or replaced. Only most of the old oil needs to be removed, the oil R12 oil is soluble in the Ester oil, but you don't want too much of it. Replace the receiver dryer and drain the compressor and you should be ok.

 Vacuum it down and check for leaks. I used to do this by injecting about 2 ounces of R12 (in the old
days, the 1970's) and then charging the system with 90psi of Nitrogen. Any leaks would be easy to find.
When the system is to your liking re-vacuum it down. In most GM systems add 6 to 8 ounces of Ester oil and charge the system with R134a. You're done for about 5 to 8 years.

The calculated amount of R134a for the stock GMC according to my AC guy is 2.9lbs.Henry

I was NIASE approved as a general mechanic, with several specialties, one of which was AC systems. The name NIASE will tell you how long ago this was, I believe it is now called ASME.     Everyone has different needs. R 406A is a fine product, has a low compressor high pressure, and is cold. If you replace your hoses you shouldn't have any problems but for your shaft seal, and that can be rebuilt. I don't know of any shops that  maintain a recovery unit for this product but I live in the boondocks, in a large town or small city I bet someone has one. You will need it because the R22 part will leak down unless you have a very tight system. That is why I prefer R134A, which does NOT cool as well, but can be filled up at home anytime. Good for old leaky cars, but I as a professional cannot service any system that leaks without repairing the leak, EPA regs. If I find a small leak at your shaft seal (almost always) I am forced by EPA regs to replace the seal or pump. Pain in the butt and big unnesessesary $.

One last thing, I know of several shops that convert to R134A by recovering all the R12, adding 4-6 ounces of Ester oil, and charging with R134A. No other changes. I don't have the balls for that but they say it works and works for years. They just don't admit that this is what they do because this is a real profit center for them.
Mark A

Wind Wings and Screens
I have made the following colored wings:
Solid -  Black, White, Light Blue, Dark Blue, Brown
See thru - Light Green, Gray, Smoked copper, Blue.
But I could get other colors.  All the hardware to install the wings are made of stainless steel.

Of course if you have wings you must have screens.  The screens I make have an aluminum frame and
fiberglass screen mess and are self contained.

If you are interested, you can reach me by
e-mail dsekula@tds.net
or phone  (765) 522-3241

By the way, I am on the digest.  I am usually several days behind in reading the posts.
Blaine Merrell
101 Way West Airpark
Bainbridge IN 46105

 Climate Control Fan Switch "off" Modification

 Fresh Air Vents

Air Conditioning Upgrades
Major change occurred in two year increments, with the best being the '77/'78 coaches. After our recommended maintenance/up-grades we were happy with the Dash A/C operation. Sealing the doors to separate the Hot from the Cold is a small job with big pay back. Also, converting the A/C into a completely air recirculation system was the biggest pay back. A simple 10 minute job for all systems except for the coaches that have the added "Air Horn" to the center/bottom dash. This system is called the "Type II" system & requires more work to achieve some Air recirculation...a half-day job, but worth it.

With my Privacy Drape closed behind the Pilot/Co-Pilot seats, recirculate mode, outside air at 100 degrees, I am able to obtain 38 degree air out of my center a/c duct. After a while, it gets too cold & we open slightly the drapes to get the desired cooling. Needless to say, we are now happy w/our a/c system. The Dash A/C can not cool the entire coach on a Hot Day (above 100 degrees), but does a great job of cooling the cockpit area.

In some cases, only adjustment of the Temperature Door for full closure makes a significant difference in cooling. Shutting off the Hot Water from flowing thru the Heater while in the A/C mode is also very helpful. The adjustment is located behind the Control Panel as an in-cable adjustment. Adjust for full Temperature Door closure as observed out front, drive side of A/C & Heater Box.Duane

DASH Heater Fire Hazard

  I thought I had an on board fire on monday when a big volume of smoke started pouring out of the a/c vents.
When I checked, I found that the heater box had a bunch of grass and debris in it that had been ignited by the blower fan resistor.


John recently posted a method for vacuuming in tight places using successively smaller sections of flexible tubing and a turkey baster. It might be helpful in cleaning debris from the heater box through the opening shown in Scott Cowden's pictures:

Bob Burkitt

Heater Blower Fan
 I found that the new AC/Delco model comes complete with a new fan cage, but costs close to $65!  I went with the Siemens motor, part number PM102/SL1587 instead for half the money.

Here are pictures of the replacement by Arch


High speed does not work

Click for Detail
Most likely your high speed blower relay is shot, or the wire that is the power feed to it has corrosion on the push on terminal.

The one you want is a NAPA ECHLIN Part# AR109.J.R. Wright

With the engine off so you can hear better, turn the key on, move the top heater / AC control lever to any setting but "max", then move the fan speed switch up to high. You should hear a 'clunk' as the relay energizes. That tells you how big your problem is. If you don't hear the clunk, then the relay coil is open or the ground to the relay is no good. You can test for voltage on the coil of the relay with a 12 volt test light.

If you hear the clunk, it could still be the relay, but most likely it is the voltage source to the relay. That wire (which I think is red) carries enough current that the push on connector can go bad. (This might be a resistance wire that is burned out.  Test for voltage at each end of wire)

An easy check is to turn the fan on high (and it won't even be running) then go out front and wiggle the whole plug assembly on the high speed blower relay. You can also check it with a 12 volt test light, the kind with an awl like pointed end is the best way to test problems like this.

> The high speed blower relay kinda' looks like a horn relay. On my '77, it is on the firewall on the passenger's side.

This is under the little access door at the passenger's front of the coach, not inside. Mark

On some of the coaches, this fan will only run when the motor is running since the power comes directly from the alternator. Gene 


AC Delay Relay On Roof Top AC
Photo Update from Larry Weidner


from Emery Stora

The fan on my dash air doesn't work in the high position, it's OK in all others - any suggestions ? 77 Birchaven- dave

Its probably the high speed blower relay or a burnt wire or loose connector to that relay.  Your 77 model also has a delay relay.  It could be that.  The information below should help you to determine and fix the problem:

I have checked over my delay relay and the blower relay and this is what I find.

The delay relay is the smaller relay at the very top of the panel. It has two leads - on mine they are brown and yellow and one has a male and the other a female terminal at the end of the leads.  The leads are approx. 6 to 8 inches long.  The female one connects to the male terminal on the lead to the blower motor.  The male one leads to the short lead (purple on mine) that goes to the blower relay (terminal 1).  If the delay relay burns out you can plug the male motor lead directly into the short female lead going to terminal 1 on the blower relay.

The blower relay (below the delay relay but above the horn relay) has 5 terminals.  When the blower relay is mounted with the 5 terminals down, there are two on the left, one in the middle and two on the right.

On the back left side it is #3 which has a red/white wire that leads to a fusible link and that goes into the harness and connects to the red wire from the alternator to the center stud of the battery isolater.

On the front left is terminal #2.  Mine has a dark blue wire that leads to the resistor package in the right side of the heater box.

In the center is terminal #1.  Mine has a short purple wire with a female connector.  The male lead from the delay relay plugs into this (on mine right now I have the blower motor plugged into this as my delay relay is bad and disconnected).

On the right rear is terminal #5.  This has a short black lead that goes to a ground screw.

On the right front is terminal #4.  This has an orange wire that leads to the heater controls on the dash.

Terminals 4 & 5 control the coil in the blower relay.

Terminals 1 & 2 are normally closed and operate the blower when in low or medium speeds.

Terminal 1 &  3 are normally open but  when the dash switch is put in "high" or "max" it actuates the coil and the relay connects these terminals which give power to the blower directly from the alternator in order to get higher voltage and higher blower speed. At the same time it disconnects terminal 2 from the circuit.

Also this

At 1:16 PM -0600 6/16/04, Emery Stora wrote:
Hi Skip - the following should give you enough info to check out the blower relay and the wiring.  The "fuse" is a fusible link that goes in the wiring from the center of the battery isolator.  There could also be bad connections with the terminals on the resistor pack that is located on the driver's side of the heater box.
(see above quoted message)

You can use a voltmeter at the various terminals to check to see if it is functioning properly.

If the delay relay is bad your high blower setting will not work. The delay relay is the smaller relay at the very top of the panel. It has two leads - on mine they are brown and yellow and one has a male and the other a female terminal at the end of the leads.  The leads are approx. 6 to 8 inches long.  The female one connects to the male terminal on the lead to the blower motor.  The male one leads to the short lead (purple on mine) that goes to the blower relay (terminal 1).  If the delay relay burns out you can plug the male motor lead directly into the short female lead going to terminal 1 on the blower relay.

And maybe this:

At 7:23 PM -0600 7/21/03, Emery Stora wrote:
  It just occurred to me that an easy substitute is to use a Bosch 5 terminal relay.  These are very, very common and found at about any parts store.  Just be sure to get a 30 or 40 amp capacity one as they come in various amp ratings.

These relays have 5 terminals marked as follows:

85 and 86.  This controls the coil.  One side goes to ground and the other to the switch on the dash blower control.  These terminals correspond to the original  relays 4 & 5 terminals.

Terminal 30.  This corresponds to the original #1.  This has the Purple wire that leads to the time delay relay or directly to the blower motor if the relay has been taken out of the circuit.

Terminal 87a.  This is the normally closed terminal that corresponds to terminal 2 on the original.  It has a dark blue wire connected to it.
Terminal 87  is the normally open terminal that corresponds to terminal 3 on the original.  A red/white wire goes to this terminal and it leads to the alternator output.

These relays are commonly found and probably a lot less expensive than whatever substitute is currently available for our original blower relays and will do just as good a job if not better

Emery Stora--