The Stovebolt Site Forums The Shop Area General Truck Talk Air Conditioning question

My '72 GMC had factory air. About 15 years ago when my dad owned it, the pully froze up and fried the belt. As near as I can tell (not knowing anything about ac) the clutch is shot. The pully turns, but the clutch is lop-sided and falls as the pully is turned. Make sense? I can buy a new clutch at NAPA and the manual says it can be replaced without removal of the compressor and, therefore, without draining the freon. The question is this. Is there a way short of looking for evidence of leaks, to know whether or not there is a need to replace more than the clutch? NAPA sells a rebuilt compressor for just a little more than the cost of the clutch, but they also say the book says to replace the other ac components at the same time. And I know from reading this involves disconnecting the hoses and draining the freon. The second question has to do with the operation of the unit. My truck emits hot air into the cab even with everything turned off. If the ac clutch is shot, does this cause hot air to be emitted instead of nothing? I'm not explaining this very well. It doesn't blow the hot air like it would with the fan on high. But at all times, there is hot air coming through the vents. I'm not sure if this is a symptom of a burned out ac clutch or if I have other issues such as relays inside the heater unit not opening the proper gate for cold vs warm air. Any ac knowledgable people out there? Thanks. The truck is a '72 GMC half-ton with factory air and a stock 402.

Right off the bat you have a problem. Units as old as your used R-12 which you no longer can get. So if the system is opened for any reason you will have to refit to R134a which is going to cost you, and I've heard the kits don't work very well due to the smaller condensor used for R12. Unless your turning the compressor there is no way to check the operation of the system I know of. Check your heater hoses to make sure your water cutoff to the heater is on the 'feed' hose to your heater. if it isn't the you will get hot air from the heater.

Rick, You are in better shape than beltfed realizes-- 2 options are available- commercial air conditioning repair places can still get r-12 but it is expensive-- just had my system recharged and the r-12 was $100-- that's the good/bad news. The really good news is a product called Enviro safe (check their web site on Google or Yahoo. It is compatible with r-12 systems without retrofitting.

Enviro is sold cheaply on eBay and works well.

Remember, if you do have to open up the system, regardless of what refrigerant is in it, it does have to be evacuated with proper reclaiming equipment.

Hey Rick, I think the 72 had the Frigidaire compressor which is a gem of a compressor in my opinion. The clutch replacement is no big deal as the part was called a "field replacement part" and requires no special tools or knowledege to replace whereas the replacement of any other component of the system will require reclaiming of the freon and flushing of the system at a minimum.

I would opt to keep that compressor and replace just the clutch and let a cerified A/C tech add the proper amount of freon. At that point you will know what if anything else you will need.

As to the second part of your question you will need to make sure the bowden cables are free and moving the proper components of the duct work and heater valve and as was mentioned be sure the heater hoses are connected for correct water flow.

Good luck!!!!!!! Hobert

My $.02-I have done this to several 67-72 trucks. First, replace the clutch if the compressor still turns OK(you can put a socket on the nut in the middle), replace the dryer w/a R134A compatible one(just about any new one), Old Air in Ft Worth makes a kit to replace the Suction Throttling Valve(weird looking gizmo near the evaporator)this changes it to a cycling clutch setup,charge w/R134A & ester oil.
The old long A6 compressor is pretty bulletproof.

To answer your first question.
If it hadn't been 15 years, you can often see where it may be leaking because some oil will come out with the freon and collect dirt.
Don't just take the hoses off. As Longbox55 said, you need to have it removed with reclaiming equipment. It is illegal to dump it into and pollute the atmosphere.
If you do decide to switch to R134A, remind the AC guy removing the r-12 that you know how much it is worth. Tell him you want a break on the parts to do the R134 conversion. He will be sticking your r-12 in someone else's system and charging the going rate.
You might just luck out and only need the clutch.

There is a fresh air vent under the cowl (outside, below windshield) on 67-72 AC cabs. The warm air may be coming in there. Not sure how hot it is where you are.

I dunno, but after 15 yrs I would be very surpised if there was any refrigerant left in the system.

Just another 2 cents worth; on at least some GM A-6 compressors, to reach the clutch you will need a special tool to get the clutch plate off. I helped my dad with one on '70 Impala when I was a kid. It is a cheap tool, but I haven't seen one for sale in years. It looks like a big bolt with a smaller bolt through it. Hope it helps. Good Luck :p

I would first hook a gauge set to it & see if there is any pressure in it. If a gauge set is not available just stick something in one of the service ports & listen for a hiss. It,s similiar to a tire stem. If the comp. seal has been leaking there will be signs of oil around the comp. clutch. It,s not hard to replace the clutch but you must have 2 special tools, one to remove the plate & one to put it on. I don,t know if they are available separatly anymore as they come in a service kit. You might be able to rent one. You may have to take it loose from the mountings & tip it up a bit but you will not have vto disconnect the hoses.

Yes me too. most compressors require a special puller. also The compressor may be stuck from sitting all that time. If it were me I would replace the compressor, reciever dryer, and orifice tube. then either convert to r134 or use the enviro system mentioned. First I would pull a vacume on the system, to make shure there are no major leaks first ( like a hose,condensor,evap core )

Thanks for all the input folks. Here's what I ended up doing. Bought a new a/c clutch at NAPA for $90. It included everything back to, and including, the coil housing. I replaced all of that and started it up. A/C clutch cycled, but no cool air. I took it to a friend who has the gauges and is certified to put charge the freon. For another $100, he added freon and it works great now. I kept it with the R-12. At first it was a little slow on the cooling after sitting for about 15 years +. But after a few cycles through, it started cooling down and now it works great. Thanks again for all the input.

Enviro Safe is a "hydrocarbon refrigerant". In plain English, that's Propane! A small leak in the evaporator will fill the passenger compartment with enough propane gas fumes to blow all the windows out of the vehicle, and kill, or at least severely burn the occupants.

Be sure the purchase of this type of refrigerant includes a good life insurance policy!
Jerry

Enviro Safe is not what I used. My system was R-12 and still is.

Rick, I noticed you refilled with R-12. Good call! Just wanted to warn others who might be tempted to use Enviro Safe that there are dangerous fumes possible in case of an internal leak. It also contaminates refrigeration gas recycling machines.
Jerry

Okay I see what you mean now, Jerry. Thanks.
Rick

Has anyone looked at the dangers associated with using 134a? From what research I have done, the flash point for 134a is lower than the flash point for the Enviro-safe. If I recall correctly, the 134a is deadlier in a confined space than Enviro-safe.

I'm not advocating using it, it just doesn't look like a good idea. But comparing the two, looks like 134a is a bigger hazard. (That's my .01cent worth)

Interesting also is hydrocarbons are used widely in Europe, where R134A is illegal.

Hey Rick, good job, glad to hear all worked out for you.

The only thing aproved by MAC,s & the EPA are R12 & R134-a.