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Sheepish Question about Air Conditioning in an 89 Suburban V2500

dbreid

dbreid

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All,
This question is coming from a little embarassment, so bear with me. I own 7 cars/trucks, all of which run fine, but none of which have AC that works. I never really cared, never tried to fix it, and basically just rolled down the windows and called it good.

Recently, my girlfriend asked me "Dan, you are so good at fixing cars, why don't you fix the Suburban's AC?" I had no real answer for her, and I realized that I actually have no way to even know how to figure out what is wrong with it....

I am looking for advice in general on how to diagnose and, if necessary, repair the system.

Here's what I have: 1989 3/4 ton SUburban with front AND rear air. All the parts are there, and I have never disconnected anything. The compressor spins freely, and the switch engages, etc. It just doesn't "blow cold". Now, I know less than nothing, but I guess I have a few choices:

1.) Get it filled and see what happens.
2.) Try to do number 1 myself. (How do I tell what the system takes? R12, 134? 123456? I have no idea!)
3.) Take it to a shop and ask them to rape me ...errrr... fix it.
4.) some combination of 1 or 2 and then fixing it myself?

Just looking for some advice.

Also, how does the rear AC work? Is it a completely standalone system? Or does it run off the front setup? COuld I fix one without the other? Or should I do both?

Thanks!!!

-Dan
 
FIrst find out if the compressor is running, if it is, then it is probably just low on refrigerent. If it is low, then you have a leak somewhere. There should be a label/tag somewhere that will tell you what type of refrigerent. More than likely it will be R-12. If that's the case, then you will have to retrofit it to R-134a. It would help if you knew somebody with gages and the right fittings so you could at least check the pressures yourself.
 
I don't know anyone with the gauges, but don't mind buying them if they aren't astronomically expensive. How much (for reference) does a typical shop charge to refill (or retrofit) to 134a?

Also, do the two systems work independently (front/rear) or do I have to deal with them both together?

-Dan
 
you should be able to get a set for about $60. I found a receipt in my glovebox from PO that had the system retrofited and IIRC it was around $500. Im not sure how the 2 systems work, but I do know that you only have 1 compressor, probably just use 2 seperate switches.
 
I myself have no idea on how to work on AC system either. I do however know that you don't have to retro fit your system. You can still get R12 (you can't buy it yourself) but a shop has to do the charge on it. If you want to try and charge the system yourself then you'll need to find someone you know that has the equipment and also has some R12 laying around. I can tell you this though, sounds like it is low on charge (probably has a leak in the system somewhere) but the leak will need to be found and fixed before you charge the system.

I've been told that R12 blows colder than the 134A
 
Actually both systems are one in the same. There is a T-fitting one on the high side and one on the low side to feed lines running to the rear unit. The rear blower motor is on a seperate switch from the front, but the compressor only functions off the front controls.:D
 
GM AC systems are pretty simple. They are what is commonly known as a CCOT (cycling-clutch orifice tube) system. The round aluminum cylinder under the hood is an accumulator (traps any liquid refrigerant that makes it through the evaporator), which has a pressure switch attached to it. When the refrigerant pressure on the low side drops to around 25psi the switch opens, disengaging the compressor clutch. Once it rises to around 40psi it re-engages. This is how it controls the evap temp and prevents it from freezing up. Of course, if there is no refrigerant in the system the pressure will be 0psi and the switch will stay open, preventing the compressor clutch from engaging (we're assuming all the HVAC controls work fine).

As others have said the reason there would be no refrigerant is because of a leak. ALL automotive AC systems leak. The main leak on a new or rebuilt system is the compressor shaft seal. It is usually a minute leak, but it grows over time. All the AC system fittings use o-rings, and they will slowly leak refrigerant due to permeation and deterioration. Likewise the old hoses were made of nitrile and will slowly allow freon to escape due to their permeability. For the most part permeability leakage is so slow that it can't be detected - the main leaks are due to deterioration of the compressor shaft seal, o-rings, and hoses. Since those things are probably the originals I wouldn't even bother with having a leak check done.

If you want to have a good-functioning long-lasting system and not be wasting your money on constant refrigerant top-offs you need to replace all of those parts. Modern AC hoses are "barrier" hoses - they are lined on the inside with nylon, which makes the hoses impermeable to refrigerant (this was necessary for R134a, which leaks through regular nitrile hoses much faster than R12). Typical replacement o-rings are made of HNBR, which is resistant to both R134a and R12 (old o-rings were nitrile). While you are at it you should replace the accumulator and orifice tube as well - this is required if you are going to convert to R134a (an 89 will be an R12 system).

On the R134a conversion matter, the performance will suck unless you swap out the old tube-and-fin condenser for a modern parallel flow type. No matter what refrigerant you use make absolutely sure your fan clutch is up to snuff.

As far as the compressor, my opinion is this: if it is an A6 (relatively long, about 6" in diameter, heavy as heck) go ahead and replace the shaft seal (they're cheap) and end plate o-rings (make sure they are HNBR if you plan on running R134a). If it is an R4 (short, large diameter, often reffered to as a "pancake" looking compressor) throw it in the garbage and get a Sanden or Seltec universal replacement compressor with the 8 mounting ears. The fittings are different, but since you will have to have hoses made anyway this isn't a biggie. A few spacers and bolts will be needed to mount it in place of the R4 - see this thread for details. Replace the condenser as well - the R4 will shed metal and plastic ring material, and it will end up in the condenser mixed with oily sludge. Then, when you fire up the system the clean, hot refrigerant gas wil break it loose, and it will clog the orifice tube (and TXV in the rear air), starve the new compressor of oil, and it will die.

The rear air is no biggie - there is a t in the liquid line which carries some refrigerant to the rear evaporator. There the flow is controlled by a thermal expansion valve. Basically, this valve regulates refrigerant flow based on the outlet temp of the evaporator. It the rear air fan is not on the evap will get cold with no temp change across it, and the valve will limit refrigerant flow to a trickle, causing most of it to go through the main evaporator. If the rear fan is cranked up the temp diff acoss the evap will cause the valve to open, allowing more refrigerant to flow. So, it is really a self-regulating setup. There will be o-rings on the rear evap setup (there should be 3, one on the inlet of the expansion valve, one on the outlet, and one on the outlet of the evaporator), and they need to be changed as well.

This probably sounds like a lot of money and effort, and it is. But, this is the only way the system will work right and last. I have seen waaaaay too many people shortcut their repairs and the results are usually bad. The system either doesn't cool well and/or it leaks or the compressor dies. Find yourself a good automotive AC components wholesaler to get your parts and hoses made. That way you won't get a$$-raped on the parts, and you get quality stuff. Do NOT get a remanned or new R4 - they are all garbage. If you replace an R4 stick with a conversion using a NEW Sanden or Seltec compressor. They should cost under $300, even with all the price hikes due to fuel costs.

Anyway, that is about all I can think of. With AC stuff I always recommend doing it right or not at all. Otherwise you will most likely end up throwing money away.

Oh, if you want a good place for info go to aircondition.com. There is lots of info over there, and plenty of knowledgeable techs usually hang out on the forum. They can probably tell you where a good wholesaler is in your area as well :wink1:
 
Well, I figured I'd post an update. I thought about it a lot, and decided that I DID want working AC, and wanted to do it right. I looked around for a reputable shop, and called to talk to them. They took the time on the phone to explain things, and talked me through conversions, etc. They repeated a lot of the things I read here, which made me feel good. I took the truck in, and (of course) my compressor was leaking like crazy, and the dryer was bad, etc. The replaced the compressor (new) dryer, and a couple of switches and connections because they were leaking, converted over to 134a (complete with appropriate stickers, etc) and charged the system.

The total cost was (ouch) 1076.00 but a huge amount of that was parts and the actual 134a itself (the Suburban takes more than 5 POUNDS of the stuff!

Yeah, it was expensive, but I feel better knowing that it was done right. And it blows ICE cold now. :)

Thanks for all the help!

-Dan
 
there is no do it yourself in ca involving ac work. you have be certified by the state to even get refridgerant. and r12 is pretty much impossible to find and too costly when you do find it.
 
I have a puzzling ac problem. I have a 96 chevy astro van with a dual ac system. I replaced the compressor, the expansion tube (the old one was not bad) and the accumulator, flushed the condenser, front and rear evaporators but didn't flush the lines going to the rear unit. It vacumed out great and held at 29 lbs overnight so I charged it up with 3 cans of freon (12 oz) each, and the tempt was blowing about 65 in the front vent but the fan wouldn't come on in the rear. The rear evaperator was ice cold with frost. The gages were about 25-40 low side, 160-180 high side. I replaced the rear ac blower switch and the fan started blowing and the high side gage almost blew the glass. I shut it off at 450 lbs! The rear evaperator lost its chill. What happened! I've got a blockage somewhere but I don't understand what happened. If the rear unit was cold before, why did it stop? Was the rear expansion valve closed and the freon stopped there, but when the switch worked, the valve opened and sent the freon back to the front and crude in rear expansion valve plugged the front expansion tube? I'm stuck. The high side inlet port stuck open and all of the freon leaked out, I guess because of the pressure being so high and maybe some crud stuck in it. wierd huh, help!
 
First off, since the system is empty now would be a good time to replace the high side service fitting - it is common for them to leak when they get old. While you're at it, pull the orifice tube and see if it is clogged with contamination. If it is, re-flush (or, better yet, replace) your condenser, flush your liquid lines (both front and rear), and replace your rear expansion valve if you can't clean it. Then recharge and try it again.
 
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