Air Conditioning Troubleshooting help

[longbedder]

OK here's the deal on my '94 Burb.

The compressor does cycle on and off normally, but it's blowing warm air.

Here are the pressure readings:
20 psi low-side compressor on
40 psi low-side compressor off
100 psi hi-side compressor on
75 psi hi-side compressor off

80 psi all around with the system off

Any ideas?

 

[4xcrazy]

low on freon and if you have a dual AC setup in that burb, make sure you run the rear one on high fan as well while doing all this testing and filling.

 

[Thunder]

Looks like you are low on refrigerant. Your high side is low depending on temp it should be 200-240
your low pressure side is way low. should be 40-55 depending on outside temp
Your static reading is at the bottom end of the scale.
When you did the running tests. Did you run the engine with the AC on high for 10-15 minutes before you took the readings?

Just from the numbers you gave.
I would add refrigerant to bring up the low pressure 40-55
high pressure 220-245
Also check for leaks.
make sure the condenser is not blocked with mud dirt ans debris.

 

[longbedder]

Did you run the engine with the AC on high for 10-15 minutes before you took the readings?

I did not. I'll try that out.

The wierd thing is that it wouldn't take any refrigerant, and thus part of the reason why I'm posting. I simply opened up one of those 12oz cans of R-134a on a valved hose attachment, but it didn't seem to take any in.

 

[Zeus33rd]

I did not. I'll try that out.

The wierd thing is that it wouldn't take any refrigerant, and thus part of the reason why I'm posting. I simply opened up one of those 12oz cans of R-134a on a valved hose attachment, but it didn't seem to take any in.

Not really the right way to do it. If it's low on refrigerant, which is what it sounds like given the pressures you reported, there's a reason for it being low. IE- a leak somewhere. You should take it to a shop and have your system serviced. For obvious reasons, it's pointless to charge a leaking system. Look at all the hose connections and crimps for wetness/oil leaks. That's the compressor oil being pushed out of the system by the pressurized refrigerant. A/C stuff is hard for most of us to work on because it takes some pretty expensive tools to do it right and legally. Trying to do it yourself will just make ya frustrated. An overcharged system is just as bad and inefficient as an undercharged system. A shop has the right equipment to evacuate, repair, vacuum and recharge your system with oil and refrigerant the right way. I'm an EPA 608/609 certified AC tech...In the past 2 months I've gone through 150+ lbs of r134a servicing and repairing our MRAP's. So I have a little experience. I don't even use the gauges or temp chart for charging the system. I just charge by weight. It's more accurate, easier and faster.

It's obviously gonna be more expensive to have a shop fix your junk, but you will be assured of a fully working system.

 

[longbedder]

Not really the right way to do it.

You should take it to a shop and have your system serviced.

I'll agree with you that simply chasing a problem with recharges is not the best plan. The reason I mentioned that is that the system would not take what was in the can for some reason. In the spirit of CK5 (which I believe to be DIY), I'd like to learn more about fixing the problem myself.

So far it looks like I've got low refrigerant level, so the troubleshooting is likely in the bag - thanks to all who posted so far. Next would be figuring out why it's low.

Two years ago I replaced the o-rings at the compressor manifold - there had been oil seeping out there. That manifold is now dry two years later. What other common leakage points on these trucks should I check (I do have rear A/C, BTW)? Do old A/C hoses leach refrigerant after a while?

Should I look into using some sort of tracer dye (and if so which is recommended)?

 

[Thunder]

It takes time for the refrigerant to enter the system. you cant just open the valve and expect the system to be charged.
To bring it up to full pressure it takes at least 10-15 minutes or so at 1500 RPM with AC on high. It is best to stick the can of refrigerant in a pan of hot water it will charge faster.....

If you have a system designed for freon R12 and you have converted over to 134A. Yes your hoses can leak. The older hoses weren't designed for the smaller molecules that 134 A is made of and after time the system will loose pressure.
My K5 has been fully converted to 134A. With the original hoses. I have no leaks in the system but i usually need to add a little refrigerant every 2 or 3 years to keep it good and cold.
As far as detecting leaks: You can get refrigerant with UV leak detector, and get a UV light and a fancy set of goggles. Or get the kind with dye in it which takes time to work..unles you have a bad leak. But IMO the best way is the old fashioned way. A spray bottle with a solution of water and dish soap. Spray all the connections/hoses with the AC on high and look for the bubbles. Simple.

 

[longbedder]

Mine takes about a year to lose the charge. I believe it was R134a from the factory.

 

[noJeepshere]

If you have a system designed for freon R12 and you have converted over to 134A. Yes your hoses can leak. The older hoses weren't designed for the smaller molecules that 134 A is made of and after time the system will loose pressure.

Thunder beat me to it. Your 94 Suburban may be in the transition year when everything was swapped from good R-12 to meh R-134. 134 coolant is smaller molecule wise, and seeps out over time. When I serviced the A/c system in my Yukon in class two years ago, a leak test with tracer dye showed no leaks, but it had only half the coolant it should (2 lbs instead of 4) It just seeps out over time and ten years was long enough to lose it. Charged it up and everything is fine, even two years later.

Since yours loses the coolant every year, you definately have a leak and I would recommend a UV dye if you insist on doing it yourself. UV dye uses yellow colored glasses and a UV light to highlight the leaks. And if you fix the leak yourself, MAKE SURE NO DIRT GETS INSIDE THE HOSES!!! If any impurities make it inside the system, you'll ruin it quite quickly. Just a word of warning.

 

[noJeepshere]

Also on the sticker on the radiator support should be the info on the A/C system and what coolant you have.

 

[Ck1500]

agree to disagree

Not really the right way to do it. If it's low on refrigerant, which is what it sounds like given the pressures you reported, there's a reason for it being low. IE- a leak somewhere. You should take it to a shop and have your system serviced. For obvious reasons, it's pointless to charge a leaking system. Look at all the hose connections and crimps for wetness/oil leaks. That's the compressor oil being pushed out of the system by the pressurized refrigerant. A/C stuff is hard for most of us to work on because it takes some pretty expensive tools to do it right and legally. Trying to do it yourself will just make ya frustrated. An overcharged system is just as bad and inefficient as an undercharged system. A shop has the right equipment to evacuate, repair, vacuum and recharge your system with oil and refrigerant the right way. I'm an EPA 608/609 certified AC tech...In the past 2 months I've gone through 150+ lbs of r134a servicing and repairing our MRAP's. So I have a little experience. I don't even use the gauges or temp chart for charging the system. I just charge by weight. It's more accurate, easier and faster.

It's obviously gonna be more expensive to have a shop fix your junk, but you will be assured of a fully working system.

I agree with taking it to a shop to have it done right!!! but i totally disagree not using gauges while charging and only weighing it in, how do you know if you have a problem? a.k.a blockage. and or other problems. being i have been in the AirConditioning field for 15 years. i would recommend weighing it in with gauges. and also check you TD "temperature drop" on system. to see what kind of split your getting. i have known people that just charge the systems until the accumulator gets cold "old fashioned way" and i would follow up with guages and correct there charge. a properly charged system is a happy system.

but this is my thoughts. im not wanting to start a pissing match here over it.

and as for taking it shops. make sure your taking somewhere thats known for A/C work.. not gas station shops and stuff.. they will end up putting the dreaded DYE in the system.

 

[Zeus33rd]

I agree with taking it to a shop to have it done right!!! but i totally disagree not using gauges while charging and only weighing it in, how do you know if you have a problem? a.k.a blockage. and or other problems. being i have been in the AirConditioning field for 15 years. i would recommend weighing it in with gauges. and also check you TD "temperature drop" on system. to see what kind of split your getting. i have known people that just charge the systems until the accumulator gets cold "old fashioned way" and i would follow up with guages and correct there charge. a properly charged system is a happy system.

but this is my thoughts. im not wanting to start a pissing match here over it.

and as for taking it shops. make sure your taking somewhere thats known for A/C work.. not gas station shops and stuff.. they will end up putting the dreaded DYE in the system.

I'm not just weighing it in with a scale and no gauges. We have a few pretty bad ass Robinair machines. As I'm sure you know, they have the gauges built in. Instead of separate scales, gauges, vacuum pumps and tanks, it's all in one unit. You can program it to be a one button affair. It'll evacuate the system, pull a vacuum for however long you program, do a leak test, inject oil, recharge to whatever weight you program in and shut itself down with only one or two button presses. Not counting any repairs or trouble shooting required, I can service an MRAP AC system from start to finish, including pulling a vacuum for 30min and charging 7.05lbs of R134a in about an hour.

This is a somewhat pointless discussion for the OP's thread anyways. He won't be weighing in anything with gauges or not. Nor is there really anything he can do to fix it himself. Legally of course. That's why we have shops and EPA certified tech's to do this stuff. And as many techs and AC guys there are, there will be just as many opinions on how things should be done.