79 Trans am: How much Freon?

Jolo

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I added r134 adaptors. How much R134 is needed to fully recharge the system?
 
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melsg5

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3.25 lbs. R12 10 oz oil, you will have to find conversion.
 

Jolo

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Thanks. I did a similar r134 conversion on an 80 mercedes 450 with no issues but I have read that the gm compressor and dryer are not compatible with 134. I don’t see how that could be correct. Any thoughts?
 

melsg5

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You have to flush the system and some feel poa valve has to be changed
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Jolo

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I am awaiting a reply from Classic Auto Air to determine if my 79 has a POA/Expansion Valve Seems post 73 models did not use the POA.
 

Jolo

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Thanks Melsg5 for the link. Very helpful. So here it is from Original Air Group/Classic Auto Air should anyone else choose to attempt this: my 79 has an orifice tube that needs replacing. I am looking into a bypass that allows the compressor clutch to engage the compressor as needed, rather than to run constantly when the ac is on.

The one issue I am having is finding a 3/8 x 24 high side R134a adaptor with a schrader valve installed. The low side (blue cap, large hose) is 7/16 x 20 and I have it, but not the high side. Advance Auto Parts has an Autocraft kit with a 3/8 high side fitting as does Auto Zone. I will check them out. Some of these kits do not have the valves. We shall see.

FROM ORIGINAL AIR GROUP
You will need to replace the O-rings, Search | Original Air Group; you will need R12 to R134a adapters, GM Charge Port Adapter Set R12 to R134a - Straight; you will need to replace the orifice tube, 1974-1999* GM Replacement Orifice Tube - Evaporator Mounted - White; you will need to flush your AC system and replace your compressor oil with 11oz of Ester oil, and you will need to replace your accumulator.
 

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Jolo

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I purchased the orifice tube, accumulator and compressor switch from PARTS GEEK. I flushed the evaporator and the condenser. Man, it took many flushes to get them clean.. I removed the compressor, drained the old oil and filled with, I believe it was, ten ounces of Ester Oil I ran a vacuum to dry out the system and to create a vacuum to receive the refrigerant until the pressure built up enough to turn the compressor on. After running the vacuum, I also let the vacuum sit for an hour with the system closed to check for loss of vacuum and leaks. No leaks. So, next step was add refrigerant. Even after having run the vacuum, the system would not accept any refrigerant with the engine running and the ac on. I then jumpered the compressor switch so the compressor came on initially figuring that would draw in refrigerant, but no luck. So, I disconnected the gauge set and tied to add refrigerate while connected directly to the low pressure port on the accumulator. Still no luck. It seems I likely have a bad compressor? Any thoughts?
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melsg5

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what pressure reading are you getting on the low side with the compressor running?
 

Jolo

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It Got to about 70 with compressor not running and I believe also with it running. I’ll run it again and verify.
 

Jolo

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You know, I wonder if I have a problem with the schrader valve on the low side r134a adapter
 

melsg5

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It Got to about 70 with compressor not running and I believe also with it running. I’ll run it again and verify.
That doesn't sound right.
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Jolo

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With the pressure switch jumped and the compressor running,.90 on the low side, no movement on the high side. Low side open, high side closed on the gauge set.
 

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melsg5

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Look at sanden.com they have diagnostics.
 

Jolo

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I checked out Sanden.com and

Seems normal gauge set readings with ac on max and compressor clutch engaged are:
low side at 25 to 35 psi and
high side at 200 to 350 psi.

When the low side reading is higher and the high side reading is lower than these ranges, the compressor is bad. The car has a remanufactured in it but it is apparently bad. I believe the car sat for years.
 
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