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AC not working after 2 days of replacing compressor

lbquoc on Fri July 18, 2008 12:47 AM User is offline

Year: 1998
Make: Lexus
Model: SC300
Engine Size: 3.0
Refrigerant Type: 134
Ambient Temp: 90
Pressure Low: 30
Pressure High: 150
Country of Origin: United States

I just had my compressor replaced with a rebuilt one due to a lock-up. New dryer, expansion valve and seals. AC blows cold air for only 2 days. Checked with dye, didn't find any leak. AC light does not blink. Pressure gauge showed 30/150psi at idle and stayed the same even at 3000 rpm. What could be the problem? clogged line? Is the compressor bad?
thanks for all the help

GM Tech on Fri July 18, 2008 8:00 AM User is offline

How much refrigerant is in it now? I would guess about half of what it needs- best way to know is to pull it out and weigh it- this will confirm you have a leak-- -that 150 head pressure is too low for 90 deg ambient-- so you most likely are low on charge-- leak is probably where it is not obvious-- I hate it when that happens- could mean evaporator..

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

lbquoc on Fri July 18, 2008 9:13 AM User is offline

I'm sure how much refrigerant is in it. My mechanic said that it's the compressor that went bad. And I don't trust the guy. I brought the compressor myself and he just replaced it. So I think he just denies that that it was his fault and blame it on the compressor to charge me to replace it again. I just want to make sure if it is indeed the compressor, not something else. Is there something I can do to figure out what the problem is?

GM Tech on Fri July 18, 2008 10:20 AM User is offline

Yeah- add more charge-- if it can pump 300 pounds on a slightly overcharge- then you know you have a good pump. then suck some out and see if it settles in to the right zone- you said it cooled good for two days- then went blah. so most likely scenarion is loss of refrigerant-- If you mechanic doesn't have a recovery machine- he is not a an A/C specialists-You need proper tools to be able to diagnose-- may be worth your while to find someone who wants to help you and can answer all your a/c questions without agendas.

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

lbquoc on Fri July 18, 2008 10:54 AM User is offline

I'll try to put more refrigerant in the system to see if it gets cold. But i'm not sure how much to add since i don't know how much is in there already. Will it cause any damage to the system if it is overcharge?

GM Tech on Fri July 18, 2008 10:59 AM User is offline

Just watch your head pressure- don't let it climb above 300 psi and you'll be fine-- You need to know if your pump works-- this is the best way- in my experience- It is hard to say you have a bad pump when it can generate high heads...no need to run it very long like that- just long enough to prove your point..

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

lbquoc on Fri July 18, 2008 11:19 AM User is offline

Pardon my ignorance but is head pressure the high side pressure? Can i use the gauge that comes with the recharge kit to measure it?
Thank you very much. Boy! am I glad i found this board.

Dougflas on Fri July 18, 2008 11:23 AM User is offline

Most likely the guage that came your kit is for the low side. try to get a proper set of guages on the sstem. try to borrow from Autozone. They don't charge for them I'm told as long as you purchase from them.

lbquoc on Fri July 18, 2008 11:28 AM User is offline

Thank you all very much for the fast response. I'll do it at luch time and report back. Thanks again

lbquoc on Sat July 19, 2008 2:27 PM User is offline


I recharged the system this morning with a 12oz can . The air was cold but not so much. So the compressor must be working. I checked the join where the expansion valve is connected to the evaporator and found some light trace of yellow dye around the thread. I think that was it. I also heard constant hissing sound around the evaporator area. Is it normal that the sound was there as long as the ac is on or you should only hear it at the beginning when the ac is fist turned on? Also i don't understand why the low side pressure stays at 45 all the time (after recharged) if it was leaking?
Thanks again

Matt L on Sat July 19, 2008 3:44 PM User is offline

You almost certainly have a variable-displacement compressor, which is designed to regulate the low-side pressure.

lbquoc on Sat July 19, 2008 4:27 PM User is offline

So even if i have a leak, the low side still show normal reading and also the pressure does not drop if i rev the engine? what about the hissing noise? is that normal?Thanks

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