A/C questions for the pros

Last season I paid a shop to fix some leaks and recharge. It was OK for the rest of last summer, but I only used it a few times.Only lately has it warmed up here and I noticed at my first usage that my A/C has been slightly warm so I figured it was a bit low. I left it for service for a week while on vacation, and when I picked it up, it still was not that cold. He had recharged it and put a "seal conditioner " in. Now the compressor will not "un-cycle" and the air is not that cold. I am an retired tech/Service manager so I know a bit about technical stuff, so I took it back to him. We went to suck it down, but the charge was low again. The tech said that last year he had put dye in, but could find no leaks this time. It held a good vacuum (-20 psi). He took out the orifice tube to look at it and blew it out. We then recharged it. It was now cool, but the compressor still will not disengage. Is it possible that the cycling switch has gone bad coincidentally with this repair ?? He subscribes to Alltrade, and there seems to be some confusion. He thinks that the cycling switch is on the accumulator, I think that's the low pressure switch and that the cycling switch is on the block on the compressor high side. Alltrade also claims that there is a one way valve and that the system doesn't have to be discharged to change the cycling switch. After it was recharged, the low side pressure was about 35 lbs running (which I thought to be a bit low) and about 150 on the high side. It was only about 75 degrees out at the time,

I have bought a new orifice tube just in case (only $2.59), and will try a cycling switch if that's what is needed. Is there any way to ohm test the switch ??

Any thoughts on this problem ??? Thanks

Anyone , please ????

Anyone , please ????

What year and engine?

The cycle switch only shuts off the compresser when it drops down to or under around 28 lbs pressure low side.

35 low side and 150 high side with compressor running sounds like a low charge or orfice tube stuck or weak compressor.
What is low side at 2K rpm with compresser running.
If it still does not cycle and drop under 28 lbs at 2K RPM it is low charge or weak compressor or orfice tube bad.

Was a full charge put in system?

THAT SEAL LEAK STUFF IS A AC SYSTEM KILLER.
Your system need gas/freon/R-12 /r-134-a or other removed/evucated and
Needs flushed out and right amount aand kind of oil and gas added to system
When a system is pumped down it should go down to and hold 30 vacuum.

After proper recharge it should cycle off at 26/28 lbs low side and back on at 35 or more lbs.

High side should range 200-250 or a little more.

Flush your system and replace the orfice tube and add proper amount of gas and oil and post back your low and hight side readings at idle and at 2K rpm.

Sorry, forgot to post: '98 Tahoe 4x4 w/5.7 engine and rear A/C. The sticker on top of the accumulator said 2 lbs 12 oz, so that was what was put back in.

What do you use to flush out the system and how??? Thanks.

Sorry, forgot to post: '98 Tahoe 4x4 w/5.7 engine and rear A/C. The sticker on top of the accumulator said 2 lbs 12 oz, so that was what was put back in.

What do you use to flush out the system and how??? Thanks.

There is your main problem.
2lbs 12 oz R-134a is for front air only.

With rear air you need a 4 lb R-134a charge.

Get a 4 lb charge in it and post back low and high side pressure at idle and at 2K RPM with compressor running and vent tempt front and rear.


When flushing you will need to add the proper amount of oil to.

Like 11 oz pag 150 oil for front and rear air.

Most parts place have a flushing agent.
Or check
AC kits.com
http://www.ackits.com/c/DIY/Do-It-Yourself+%28DIY%29+Starter+and+Advance+Kits.html

Post back how it goes.

Is the belly of the compressor oily/greasy? If so, there is your leak- very, vey common. Also does compressor spin very easily by hand- like you can turn it with only one finger? Are there little "catches" as you rotate compressor drive plate? If so, you have an internal suction reed failure, and is why the system won't suck doen below 30 psi low side.....

Last season I paid a shop to fix some leaks and recharge. It was OK for the rest of last summer, but I only used it a few times.Only lately has it warmed up here and I noticed at my first usage that my A/C has been slightly warm so I figured it was a bit low. I left it for service for a week while on vacation, and when I picked it up, it still was not that cold. He had recharged it and put a "seal conditioner " in. Now the compressor will not "un-cycle" and the air is not that cold. I am an retired tech/Service manager so I know a bit about technical stuff, so I took it back to him. We went to suck it down, but the charge was low again. The tech said that last year he had put dye in, but could find no leaks this time. It held a good vacuum (-20 psi). He took out the orifice tube to look at it and blew it out. We then recharged it. It was now cool, but the compressor still will not disengage. Is it possible that the cycling switch has gone bad coincidentally with this repair ?? He subscribes to Alltrade, and there seems to be some confusion. He thinks that the cycling switch is on the accumulator, I think that's the low pressure switch and that the cycling switch is on the block on the compressor high side. Alltrade also claims that there is a one way valve and that the system doesn't have to be discharged to change the cycling switch. After it was recharged, the low side pressure was about 35 lbs running (which I thought to be a bit low) and about 150 on the high side. It was only about 75 degrees out at the time,

I have bought a new orifice tube just in case (only $2.59), and will try a cycling switch if that's what is needed. Is there any way to ohm test the switch ??

Any thoughts on this problem ??? Thanks

You are welcome.

You are both right on compressor cycle pressure switch.:rofl:

The AC compresor cycle switch is on low side at accumulator.
But it also has aa AC low pressure cut out switch on the compressor.

Not sure of cut off pressure but compressor should cut out around 28 or lower pressue.
Also at low idle compressor may cut off.
Always check with idle speed up a little.

the switch on the back of the compressor is a high pressure cut-out switch normally closed, it opens at 427 psi.....the cycling switch serves dual purpose- averts evap freeze-up, as well as low refrigerant charge protection...(and cold weather operation)

the switch on the back of the compressor is a high pressure cut-out switch normally closed, it opens at 427 psi.....the cycling switch serves dual purpose- averts evap freeze-up, as well as low refrigerant charge protection...(and cold weather operation)

The ac wiring diagram for the 98 tahoe shows both a high and low pressure switch on back of compressor.
Plus a low pressure cut off on the accumlator.
Best I can figure the low pressure switch on compressor is a cut out switch for to low of a engine idle.

But I have figured wrong before.

There is your main problem.
2lbs 12 oz R-134a is for front air only.

With rear air you need a 4 lb R-134a charge.




So the sticker on the accumulator is wrong?? It states Tahoe w/rear air 2lbs 12 oz and Suburban w/rear air 4 lbs. As far as I can tell, the only rear air on a Tahoe is duct work. There is no expansion valve and rear evaporator. The accumulator is the original and has always been charged to those specs. I will try to get some pictures tomorrow of the sticker and also the switches. I went to the Chev dealer and got a picture of the parts print out. They call the switch on the accumulator the clutch cycling switch.

So the sticker on the accumulator is wrong?? It states Tahoe w/rear air 2lbs 12 oz and Suburban w/rear air 4 lbs. As far as I can tell, the only rear air on a Tahoe is duct work. There is no expansion valve and rear evaporator. The accumulator is the original and has always been charged to those specs. I will try to get some pictures tomorrow of the sticker and also the switches. I went to the Chev dealer and got a picture of the parts print out. They call the switch on the accumulator the clutch cycling switch.

If it has rear AC unit put 4 lbs in it.

If the system is overcharged the high side will go way up also low side will rise.

So the sticker on the accumulator is wrong?? It states Tahoe w/rear air 2lbs 12 oz and Suburban w/rear air 4 lbs. As far as I can tell, the only rear air on a Tahoe is duct work. There is no expansion valve and rear evaporator. The accumulator is the original and has always been charged to those specs. I will try to get some pictures tomorrow of the sticker and also the switches. I went to the Chev dealer and got a picture of the parts print out. They call the switch on the accumulator the clutch cycling switch.

Yes sticker is wrong or from another truck or year.
All of my repair info says 4 lbs for a 98 SUB.,Tahoe,Yukon.

What did the dealer say the AC charge was?

On the rear head of the compressor itself there is and has only ever been one switch port on a Delphi HT-6 - I know these compressors intimently!-- There may be a recirc door switch on the piping at the compressor outlet which your wiring diagram shows...and lists as at rear of compressor.

As far as whether or not you have factory rear air-- pretty easy- are there two pipes (5/8") at the accumulator that join? Is there a split or "Y" just beyond the condenser outlet at the right side frame rail? - Are there two aluminum pipes (5/8" & 3/8") that join with the two heater pipes (optional) that run back to the right side of rear compartment? If all above are true- and you have the controls for rear air (and/or heat) above your head and above passenger's head- then here's your sign that you have rear air conditioning.

Look inside the glove box door for the Service Parts Identification sticker. Look for C60 (front A/C) and C69 (rear A/C). If you have the C69 then you have the full rear A/C and should follow the previous post advising the proper charge which is 4 lbs. If you do not have the C69 then the proper charge is 2.25 lbs.