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FriendlyMan

Air Conditioner: new compressor stopped cycling

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2000 Chevy Silverado 1500 4.8L V8 Manual Transmission

Last summer I ordered a complete new AC system: new compressor, drier, condenser, orifice tube, etc. The only thing I did not change out were the lines and the high and low fittings on them. I did thoroughly clean out the hoses though, and the evaporator. Well after that all night long project, I pulled vacuum for another 8 hours, made sure there were no leaks, and then refilled it with R-134A. I did put the proper amount of PAG oil in the compressor and even verified that I had the correct oil for the compressor. If you are wondering why I did not replace the lines as well....well, at that point I reached the max of my budget to fix the AC, but they were in good condition anyway. I did replace all of the o-rings too.

Well the AC worked just wonderfully all summer after that. No leaks, no issues what so ever. Then came winter this year and I did not run the AC at all. When it started warming up last week (I am from Louisiana) I decided to run the AC... No cold air. OK Hmmm... When I got home I decided to look under the hood and everything appeared fine until I unscrewed the high side fitting cover and then I hear and see refrigerant spewing out, Damn! I thought. The little rubber valve in there was deformed and the cap was all that was holding the pressure in.

SO I am a little red faced that after $600+ project, I am defeated 6 months later by a $2.50 part I did not switch out.

Yesterday I had the refrigerant removed, I took the old fitting off and put a new one on. I pulled vacuum for an hour, waited to check for leaks, there were none, so I ran the vacuum pump for another hour. Then I started the refrigerant refill process again. The compressor would not cycle or stay on, the only way I could get it to take in refrigerant was to disconnect the wires on the pressure switch and connect the terminals to help it get started. After about 2lbs of refrigerant, the compressor still wont cycle. Still no AC...

Pressure switch dead? maybe. Its still a bit new though, so IDK. I have noticed that the low and high side pressures are not getting as high as they were when I first put the new one in. So I am wondering if my gauges leaked and air got in there some how? Perhaps I did not evap all of the moisture? There seems to be plenty of oil in there (I can see it in the gauge sight glass--could that be water?)

I am hoping a discussion can help me figure out what is going on...I want to take my honey bunny on a little honeymoon road trip and I need my trucks AC.

What do you guys think?

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2000 Chevy Silverado 1500 4.8L V8 Manual Transmission

 

Last summer I ordered a complete new AC system: new compressor, drier, condenser, orifice tube, etc. The only thing I did not change out were the lines and the high and low fittings on them. I did thoroughly clean out the hoses though, and the evaporator. Well after that all night long project, I pulled vacuum for another 8 hours, made sure there were no leaks, and then refilled it with R-134A. I did put the proper amount of PAG oil in the compressor and even verified that I had the correct oil for the compressor. If you are wondering why I did not replace the lines as well....well, at that point I reached the max of my budget to fix the AC, but they were in good condition anyway. I did replace all of the o-rings too.

 

Well the AC worked just wonderfully all summer after that. No leaks, no issues what so ever. Then came winter this year and I did not run the AC at all. When it started warming up last week (I am from Louisiana) I decided to run the AC... No cold air. OK Hmmm... When I got home I decided to look under the hood and everything appeared fine until I unscrewed the high side fitting cover and then I hear and see refrigerant spewing out, Damn! I thought. The little rubber valve in there was deformed and the cap was all that was holding the pressure in.

 

SO I am a little red faced that after $600+ project, I am defeated 6 months later by a $2.50 part I did not switch out.

 

Yesterday I had the refrigerant removed, I took the old fitting off and put a new one on. I pulled vacuum for an hour, waited to check for leaks, there were none, so I ran the vacuum pump for another hour. Then I started the refrigerant refill process again. The compressor would not cycle or stay on, the only way I could get it to take in refrigerant was to disconnect the wires on the pressure switch and connect the terminals to help it get started. After about 2lbs of refrigerant, the compressor still wont cycle. Still no AC...

 

Pressure switch dead? maybe. Its still a bit new though, so IDK. I have noticed that the low and high side pressures are not getting as high as they were when I first put the new one in. So I am wondering if my gauges leaked and air got in there some how? Perhaps I did not evap all of the moisture? There seems to be plenty of oil in there (I can see it in the gauge sight glass--could that be water?)

 

I am hoping a discussion can help me figure out what is going on...I want to take my honey bunny on a little honeymoon road trip and I need my trucks AC.

 

What do you guys think?

Lower pressures don't necessarily mean something is broken. What pressures are you running?

 

Keep in mind A/C system pressures vary greatly with heat load. If your reference was in 100 degree temps with humidity compared to 75 degrees recently, expect pressures to be quite a bit lower.

 

Check A/C pressure transducer PIDs on a scantool and see what they're reading. They are what informs the PCM of your pressures which controls your compressor.

 

If you have the correct charge in the system but no compressor operation, you need to acquire a wiring diagram of the A/C system. Pretty simple system electrically. Likely a safety switch has failed and is preventing the compressor from engaging.

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yeah, if the compressor will run when you jump out the wires, I would be looking for a relay or sensor that needs replacement.

 

+1 on the pressures being lower with lower ambient temperatures. they have charts you can look at that will show what the pressures will look like at any given temperature. Normally you also look at the differential. When a compressor goes bad or develops an internal crack, you don't get the differential that it should have.

 

Good luck tracing the wiring. Shouldn't be too difficult.

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Luckily I wrote down the pressures the system had when it was working. 55 psi low side and 260 high side, and this was something like 95 degrees F outside. When I jump the wires and fore the compressor to come on, it does 50 low side and 160 high side.

I will look into a safety switch and relays. Quick question though, where can I get the AC schematic for my truck? The haynes manual I have is not specific enough when it comes to A/C.

Also, does my truck have an ambient temperature sensor? If so where is it? I could not find anything looking like it behind the grill.

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I'd check the low pressure cut-out switch.

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If you have a ambient temp. sensor and it is reading below 37° or 38° it won't let the compressor to engage.

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Luckily I wrote down the pressures the system had when it was working. 55 psi low side and 260 high side, and this was something like 95 degrees F outside. When I jump the wires and fore the compressor to come on, it does 50 low side and 160 high side.

 

I will look into a safety switch and relays. Quick question though, where can I get the AC schematic for my truck? The haynes manual I have is not specific enough when it comes to A/C.

 

Also, does my truck have an ambient temperature sensor? If so where is it? I could not find anything looking like it behind the grill.

55psi is above spec for most any air conditioning system. The system should be cycling from 20-40psi on the low side, give or take a few psi. 260psi is also pretty high, but could possibly be normal if there was a high cooling load.

 

What are your pressures on a cold engine with the system NOT running? Also, please let us know what the temperature is when taking these readings.

 

If the aforementioned 55/160 is on a cold engine with a non-running system, it sounds like the system is overcharged.

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i hope this helps ,i may post another

 

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Thank you so much for the schematics. I replaced the pressure switch and changed out the orifice tube. The orifice tube was a little dirty. :(

After refilling it seems to be working now.

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