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Tractor Talk Discussion Forum

O/T 93 Suburban a/c problem

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Gene Davis (Ga.

10-11-2005 19:33:09




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Maybe this is off the tractor topic, but is definitely a very great obstacle to it! Have a serious problem with the A/C in a Chev Surburban. Wife isn"t going allow any work on my Earthmaster tractor restoration till I get this one solved! Drove our 93 Chev.Suburban Sunday to church and back home it cooled good as always. She drove it to dr appt Monday and came in and annouced that it had quit cooling. Raised hood with A/C on and the compressor cycles on and off constantly in about 30 second intervals, runs smoothly with no noise or vibration. It doesn"t run long enough to tell if there is much difference in the suction and discharge line temperatures. There are no indications of leakage that show,or oily spots. System still has R-12 in it. Had it checked and added 1 lb to the system earlier this year,which is not much considering it has the front and rear units. It has never been opened since new. Could this be caused by the innards of a drier disintergrating and having caused a restriction in the system? It has the original drier in the system.

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Garry F(NC)

10-12-2005 18:40:53




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 Re: O/T 93 Suburban a/c problem in reply to Gene Davis (Ga.), 10-11-2005 19:33:09  
Gene, The pressure cycling switch(screwed into the accumulator usually) for R-12 are set to cycle off at around 24 psi in order to keep the system above freezing. Unplug the harness plug from the switch and jump across it ( I have even used a large paper clip un folded) Run the A/C if the pressure goes down into the 20-25 (low side) pretty fast it is probably a low charge. If the high side service port is the the liquid line like a lot of GM vehicles, the high side pressure reading will likely be around 150-200 with correct charge after the vehicle is cool inside.The liquid line is between the condenser and orifice tube. A clogged orifice tube will usually make the low side low and the high side too high (because of restriction) though this would be somewhat different on a vehicle with rear A/C. With a proper Refrig. charge a good rule of thumb is that the suction line should be good and cool and sweaty all the way to the compressor. I live in about the same climate,humidity etc. as you. Also check your radiator fan clutch for proper operation. With the vehicle at operating temp. when you stop the engine the fan should only 'coast' a few blades and stop, not keep spinning several revolutions. A bad fan clutch would not have anything to do with rapid cycling though. I have had pretty good luck converting to R-134A with most everything and the price of ot has peaked and come down some lately. To all you folks on this site, I have been reading it for several years and really enjoy all of the forums. Gene, email me if you have any questions
Garry F.

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jdemaris

10-12-2005 05:49:43




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 Re: O/T 93 Suburban a/c problem in reply to Gene Davis (Ga.), 10-11-2005 19:33:09  
The frequent cycling is usually an indication of a slow leak and being low on refrigerant. If you temporarily put a jumper-wire on the harness connector to the low-pressure switch, it will probably smooth out. This switch has a screw-slot in it and can be adjusted also. That won't fix a low gas pressure situtation, though. I've got several Suburbans (87, 99, and 91) and I had to convert them all to 134A. It works fine. Keep a few things in mind. First, many Suburbans have rear AC as well as front, and the long aluminum lines that run front to rear tend to spring leaks where they are clamped. That is caused by GM using steel clamps against aluminum lines which causes an electrolytic reaction (like battery corroision). I've replaced all of mine with rubber AC hoses - but I live in central NY in the rust-belt. Maybe you don't have that problem. Also keep in mind that AC hoses made for older R12 systems are not suitable for 134A. The molecular structure of 134A is smaller than that of R12 which enables it to pass though the older type rubber AC hoses very slowly, but surely. That's why they were all changed to "barrier" hoses now. The newer hoses have a plastic liner inside of them, thus the name "barrier." The GM system you have is prone to orifice-tube plugging. You should inspect your system for leaks - you might see it by the presence of oil by a trouble spot. You can also use a professional leak detector (if you have access to one), or, make an adaptor and hook compressed air to your system and listen for leaks. Chances are though, in your case, you've got a very slow leak. Once you find your leak or leaks, and the system is empty, pull the orifice tube and check it - it usually has trash on it. If you have rear AC, the rear unit also needs to come apart for cleaning.

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hay

10-12-2005 05:07:47




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 Re: O/T 93 Suburban a/c problem in reply to Gene Davis (Ga.), 10-11-2005 19:33:09  
just a bit of friendly advice: DO NOT, i repeat, DO NOT change it over to the newer R134a if you can possibly avoid it. IF you can get original R12 put back into the system, it is worlds better than R134a. i had the conversion done on my 93 pickup and the cooling with R134a is greatly diminished. about 30% less cooling ability and won't even cool unless driving at highway speed. i know something is wrong, but every mechanic says the R134a does not cool as good as the R12 freon. i wish i would have never converted it now. and living in a hot humid climate there is a lot of difference in comfort.

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Allan in NE

10-12-2005 04:35:48




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 Re: O/T 93 Suburban a/c problem in reply to Gene Davis (Ga.), 10-11-2005 19:33:09  
Gene,

GM has been cycling that compressor on and off since way back about 1980. You live down south in a hot, humid climate where your compressor has to work hard, so you folks don"t see "em cyclin" off and on like we do up here further north.

The fact that it is cycling "quick" perhaps "might" be a bad switch (one"s first inclination), but I really doubt it. The system is telling you something is wrong.

Either the system is low on Freon or that orifice tube screen is plugged with debris. Either way, I don"t think it is serious; just needs attention and I"m bettin" on a slow leak somewhere.

Hope ya get "er goin,

Allan

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thejdman01

10-12-2005 04:25:30




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 Re: O/T 93 Suburban a/c problem in reply to Gene Davis (Ga.), 10-11-2005 19:33:09  
start grabbing the lines. from the compressor the the condensor the lines should be hot warm to the touch from the expansion valve to the evaporator should be cold. from the evaporator to compressor should be ambient temperature. sometimes lines from the condensor to the expansion valve collapse and create a sort of another expansion valve. this should give you a general idea of what should be happening and depending on what isnt right should be where your problem is. let us know.

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Allan in NE

10-12-2005 04:41:24




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 Re: O/T 93 Suburban a/c problem in reply to thejdman01, 10-12-2005 04:25:30  
Mornin,

GM vehicles haven"t used an expansion valve since about 1979.

As I recall, the last one of those dinosaurs was on the big Buick with the 6 cylinder compressor.

Allan



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jdemaris

10-12-2005 08:25:13




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 Not true in reply to Allan in NE, 10-12-2005 04:41:24  
Although most G.M.s use the cycling-switch orifice valve systems, most with rear AC also use an expansion valve. All three of my Suburbans and also my 94 Astrovan have an thermal expansion valve in the rear AC unit.



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Deane

10-12-2005 02:47:04




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 Re: O/T 93 Suburban a/c problem in reply to Gene Davis (Ga.), 10-11-2005 19:33:09  
Ask here, these guys are good.
http://www.autoacforum.com/



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Kevin (FL)

10-11-2005 20:37:46




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 Re: O/T 93 Suburban a/c problem in reply to Gene Davis (Ga.), 10-11-2005 19:33:09  
Gene,

We just went through the same thing on our '95 diesel Suburban and I changed out the LP cutout switch. Seems it was causing the clutch to cycle off and on while running. After a few weeks of that, it would just stay off. I also noticed that when I pushed against the switch it would work--at that point I thought it was just a loose connection on the wiring. Might not be the same problem with yours but you might try working the switch back and forth a little to see if you can make it work (temporarily) and then go buy a new one. You'll loose a tiny bit of coolant when you unscrew the switch but not enough to matter.

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Jon Holt

10-11-2005 20:07:31




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 Re: O/T 93 Suburban a/c problem in reply to Gene Davis (Ga.), 10-11-2005 19:33:09  
If the system is charged correctly, a faulty cycling switch on the accumulator can cause this problem. There could also be a restriction in the system.



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