Another A/C Issue

[febtober]

Looking for a little help with an AC issue on my 2000 LS8.
Background: I bought this from my cousin last fall, knnowig it had a laundry list of issues.
Right now, I want to ry and tackle the AC. He bought it 7-8 years ago and said the AC never worked. The engine was replaced about 3 years ago, I assume the AC was never looked at. All the lines look ok, no rust, no oil residue at fittings or on the compressor, etc. I know a visual inspection cannot indicate whether or not it is really OK, I'm just saying there is nothing obviously wrong.
The compressor does not engage when I lower the temp in the cabin. I read that there were 2 pressure switches, but I can only find 1, the one near the top of the condensor that is labelled as transducer in some of the diagrams I have seen. Anyway, as soon as I DISCONNECT this sensor, the compressor engages. What does this mean? From what I read, you should be able to jump out a bad switch to make the compressor run, not open the circuit. I tried it 5 times to make sure something else was not going on. Unplug switch, compressor runs.
Which switch am I testing, high pressure or low? What does my test indicate? Is the switch bad? Is there another switch?
Also, I checked the pressure on the low side, no surprise, there was no pressure. I am assuming that this is because of the past non-use and engine replacement.
My cousin was not a good LS owner, he could never keep up with the upkeep, never had it properly serviced, and it would not surprise me in the least that it could simply be a bad switch. It could also be something major.
My next thought was to obtain some r134a and see what happens. It will be difficult here in WI, but the Iola car show is next week, I should be able to find some.
My desire is to do a couple easy, inexpensive tests and hope to get lucky. I know, luck factors in very little dealing with these cars.
I would appreciate any help you may have to offer.
Thanks,
Febtober

 

[scjmc]

If the low side pressure is zero then the computer would never engage the compressor. If my understanding is correct the computer needs to see some pressure to engage the compressor. Try adding refrigerant (oil too maybe...). You might have to unplug that transducer that you were talking about to force the compressor to run while you add 134. Keep in mind that running the compressor with no pressure in the system will kill it because it needs the refirgerant to carry its lubricating oil. I live in Florida and 134a is easily avilable in auto parts stores. Is it not in the north?

 

[SlickLS]

If the low side pressure is zero then the computer would never engage the compressor. If my understanding is correct the computer needs to see some pressure to engage the compressor. Try adding refrigerant (oil too maybe...). You might have to unplug that transducer that you were talking about to force the compressor to run while you add 134. Keep in mind that running the compressor with no pressure in the system will kill it because it needs the refirgerant to carry its lubricating oil. I live in Florida and 134a is easily avilable in auto parts stores. Is it not in the north?

+1 Good advice right here

 

[febtober]

Refrigerant not available in WI thanks to the legislators in The People's Republic of Madison.

Thanks for the advice.

Are there 2 pressure switches?
Which one did I unplug?
Where is the other one?
Why did the compressor run when unplugged?
I am trying to determine whether or not the switch is bad.

Thanks again!
Febtober

 

[joegr]

Refrigerant not available in WI thanks to the legislators in The People's Republic of Madison.

Thanks for the advice.

Are there 2 pressure switches?
Which one did I unplug?
Where is the other one?
Why did the compressor run when unplugged?
I am trying to determine whether or not the switch is bad.

Thanks again!
Febtober

The pressure transducer is working correctly. The compressor is not allowed to run when there is no pressure. Disconnecting the transducer and allowing the compressor to run with no charge is doing major damage, even if only for a few seconds.

Just putting R-134 in may result in a working system for a little while, but it will not work for long.

You need to:

1. Find and repair leak(s).
2. Replace the receiver/dryer.
3. Pull a vacuum on the system.
4. Charge with the correct amount of compressor oil.
5. Charge with the correct amount of R-134.


Description of the pressure transducer from the manual...

A/C Pressure Transducer

The A/C pressure transducer monitors the compressor discharge pressure and communicates with the powertrain control module (PCM). The PCM will interrupt A/C compressor operation in the event that the A/C pressure transducer indicates high system discharge pressures. It is also used to sense no or low charge conditions. If the pressure is below a predetermined value for a given ambient temperature, the PCM will not allow the clutch to engage.

The A/C pressure transducer is mounted on a Schrader valve-type fitting on the A/C compressor to condenser discharge line.
A valve depressor, located inside the threaded end of the A/C pressure transducer, presses on the Schrader valve stem and allows the A/C pressure transducer to monitor the compressor discharge pressure.
When the compressor discharge pressure rises, the PCM will interrupt the A/C compressor clutch coil circuit and disengage the A/C compressor. When the pressure drops, the PCM will enable the A/C compressor circuit. For specifications regarding operating pressure(s), refer to the Powertrain Control/Emissions Diagnosis (PC/ED) manual.
It is not necessary to discharge the refrigerant system to remove the A/C pressure cutoff switch.

 

[febtober]

Thanks for clarification. I was puzzled by people saying to unplug the transducer and use a jumper to get the compressor to engage, and mine only ran when it was totally unplugged.

I am only looking at the AC as an afterthought, as I figured it was trashed from years of neglect. I am trying to determine how trashed as inexpensively as possible. We only have 12 days of Summer up here anyway

I will proceed cautiously, thanks for the tip on the dryer.

Thanks again!
Febtober

 

[chocolat1701]

First do this get 7 ounces of pay oil and then your system needs 28 ounces of r134get the one with the leak detector and sealer. Order it online on eBay or AutoZone and have it delivered to you. Use the low side and fill it you may have to manually engage the compressor like you did before. Put the pag oil first you put refrigerant first you will kill the. Compressor try this before you change out anything else since at this point if you take it to a repair shop this is what they are going to do. They are going to fill it, look fir leaks and test compressor to see jf air comes out and they will charge you a boatload just for this and you can do this yourself. By the way get the pag oil can that you can use on the low side ov the compressor most of the oils you have to remove the compressor and pour in the oil manually.

 

[milehighmikey]

I found that when you hook up the can to a vacuumed or otherwise empty system, let the refrigerant pressurize the system and equalize it to the can pressure, the compressor will turn on with no other steps required, as long as the system can hold pressure, even if just temporarily. (assuming a leak small enough that allows some pressure building up, or hopefully, no leak at all)

 

[chocolat1701]

You are correct I just replaced my ac compressor and the system was empty and the compressor turned on if I remember you have to set the temp to 60 and the fan to high and then pump the new oil and r134 in.

 

[febtober]

Update, now that it is hotter than fudge up here.

Added a charge of refrigerant/oil/leak detector. Blew cold for a while, until refrigerant ran out of a very small gash at the very bottom of the condenser. No leaks anywhere else, no bad noises from compressor, it engaged like it should after things came up to pressure. No oil leak from compressor, either.

I have a new condenser on the way, it looks easy enough to change out.

What are the steps after I replace the condenser? I want to be as cheap as possible and don't want to replace any other parts. I know this may not be ideal, but I just don't care all that much.

Thanks again!

 

[joegr]

So, you ask for the steps, but then say that you won't follow them?


Replace receiver/dryer.
Pull vacuum on system for a few hours.
Refill with R-134a and oil.

 

[febtober]

Ok, maybe I would replace the drier if it is a good idea, I can get them cheap off ebay.......

 

[febtober]

Wow, thanks for the quick reply.

Yes, I guess that seems pretty half-butted. Sorry, the heat is getting to me.

Let me rephrase: I will replace the drier, is there anything else I should replace? I am confident the compressor is good, and I really don't want to mess with the whatsit under the dash.

If I am not replacing the compressor, how much oil do I add?

Thanks for your patience

 

[joegr]

Wow, thanks for the quick reply.

Yes, I guess that seems pretty half-butted. Sorry, the heat is getting to me.

Let me rephrase: I will replace the drier, is there anything else I should replace? I am confident the compressor is good, and I really don't want to mess with the whatsit under the dash.

If I am not replacing the compressor, how much oil do I add?

Thanks for your patience

The best thing is to drain all the oil out an put 7 oz of oil back in, but that may not be practical.
It should take 28 oz of R-134a.

http://deneau.info/ls/s6x~us~en~file=s6xc0001.htm~gen~ref.htm
http://deneau.info/ls/s6x~us~en~file=s6xc0011.htm~gen~ref.htm
http://deneau.info/ls/s6x~us~en~file=s6xc0014.htm~gen~ref.htm