HELP: New A/C Compressor not coming on

[wiseman]

I once checked out a book from the local library on a/c repair. However I don't remember enough to help you.....except for recommending your local library. The book also prepared you for the ASE exam. It covered how to charge the a/c, how to read the gauges, types of freon, etc.

Thanks for the feed back GNRick. I have been doing alot of research to figure this situation out.

 

[wiseman]

I have a question or something that I have noticed about the target pressure of 30-35psi on the low side and the 280psi on the high side. Yes, I have found these numbers to be accurate per and are straight out of the GM Turbo Regal Repair manual (See attachement 1), but those numbers are based off of R12 refrigerant. Since R134a operates at "almost" twice the operating pressure of R12, shouldn't that make the GM based manual not applicable for R134a retrofits?

I also found the "Performance Air Chart" in the manual (See Attachment 2).It states that @ 90 degrees F , the air discharge is 36-43 degrees F (thru vents), 200-245psi on High Side, and 26-35psi o low side.....which is fine for R12.

Now for R134a, the chart shows (See attachment 3) that the manifold gauge on the low side should read 45-55psi and 250-270psi.

Should I use the R134a chart numbers or the R12 numbers from the GM Manual (Even though I am using R134a)??????

 

[RmvBfrFlght]

Use the R134a pressures. You may also need to adjust the pressure cycling switch on the accumulator.

RemoveBeforeFlight

 

[wiseman]

Use the R134a pressures. You may also need to adjust the pressure cycling switch on the accumulator.

RemoveBeforeFlight

Would I decrease or increase the setting of the cycling pressure switch?

Posted from the TurboBuick.Com mobile app

 

[dr_frankenstein]

did you upgrade the orfice and condensor when you decided to use R134A?

R134a is marginal at best on the old R-12 stuff. particularly is you have a sepentine condensor.

 

[wiseman]

Yes,...I did a "Type 1" retrofit. New dryer, orifice, condensor, and brand new compressor (not a reman.). I flushed the evap. Core and all lines throughly. Vacuumed the system and filled with synthetic r134a.

Sent from my PG86100 using TurboBuick Mobile mobile app

 

[dr_frankenstein]

sweet, just double checking

 

[wiseman]

Ok, thanks!

I will go home and add the refrigerant that I took out of the system early this week. Since I can't measure it accurately, I will check the ambient temperature, then check the chart to see how much pressure should be in the system, and add refrigerant as needed. That should get me close..........

Sent from my PG86100 using TurboBuick Mobile mobile app

 

[RmvBfrFlght]

Would I decrease or increase the setting of the cycling pressure switch?

Posted from the TurboBuick.Com mobile app

Need to lower the pressure at which the switch will cycle. Try it at 21 - 22 psi, IOW, once the compressor is engaged that switch won't open until the low side drops to 21 psi. The adjustment screw is under the electrical connector.

RemoveBeforeFlight

 

[wiseman]

Need to lower the pressure at which the switch will cycle. Try it at 21 - 22 psi, IOW, once the compressor is engaged that switch won't open until the low side drops to 21 psi. The adjustment screw is under the electrical connector.

RemoveBeforeFlight

Ok, thanks a bunch, I adjusted the pressure switch to 21psi. Thanks again......

 

[wiseman]

A/C Dryer/Accumulator Low Pressure Switch

Here is some FYI info in case someone else is trying to find the P/N for the low pressure switch. I couldn't find it anywhere on the forum.

1) GM OEM P/N: 3040500 - (For R12) - A/C Dryer Low Pressure Switch

2) O'Reilly P/N: 35751 - (For R12) - Murray® Climate Control - System Mounted Cycling Pressure Switch
http://www.oreillyauto.com/site/c/d...k=Search_01957_1035795_507&pt=01957&ppt=C0039

3) O'Reilly P/N: 36674 - (For R134a) - Murray® Climate Control - System Mounted Cycling Pressure Switch
http://www.oreillyauto.com/site/c/detail/MRY0/36674.oap?ck=Search_36674_-1_507&keyword=36674

Note: The picture is misleading. The "circular extruded feature" that extends past the 2 terminals are only for protection of the terminals. This circular area slides off to expose the terminal prior to installation.