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Newly Rebuilt R-12 System Does not Cool

mrpate on Thu May 24, 2012 12:08 PM User is offline

Year: 1967
Make: Chev
Model: Corvette
Engine Size: 327
Refrigerant Type: R-12
Ambient Temp: 90
Pressure Low: -15" hg
Pressure High: 150
Country of Origin: United States

This winter I decided to rebuild the R-12 AC system in my 67 small block car. I did the following to the car.

1. Replaced the shaft seal in the compressor.

2. Had the filter Dryer rebuilt.

3. Replaced the incorrect expansion valve with the correct J clamp style bulb (purchased from Corvette Central).

4. Bench tested the POA valve. Relieved at 32 PSIG.

5. New hoses and clamps.

6. Added 10 oz of new refrigerant oil.

Triple evacuated entire system and pulled the system down to 250 microns and pressure did not rise above 500 microns after 12 hours.

Using a dial-a-charge I transferred just over 3 lbs of R-12 with the compressor in operation. Blower fan was in the high position.

The ambient temperature was 90 degrees F

After 5 minutes of operation the head pressure was 150 lbs and the suction pressure was 15 inches of hg. The suction pressure did rise to 0 psig once during the test and then returned to approximately 10" hg before I shut the system down.

The sight glass is free of bubbles.

It almost appears that the new expansion valve is malfunctioning and simulating a pumped down condition.

I do not have a refrigerant recovery device and I just added my last three pounds of R12 so I am very interested in suggestions from this forum that first address corrective action that does not include opening up the system initially.


GM Tech on Thu May 24, 2012 12:17 PM User is offline

I'd be tapping the snot out of that TXV-while it is running- it appears to be stuck- since you are running in a vacuum-- could it be POA stuck as well? I'd tap on it too.-- with a ball peen whammer.

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......

mrpate on Thu May 24, 2012 4:40 PM User is offline

GM Tech

I followed your advice using the hammer on the expansion valve. I also placed the thermal bulb in boiling water and then into an ice bath for a couple of cycles. Still did not work.

Time to open up the system


Dougflas on Thu May 24, 2012 4:57 PM User is offline

Remove the TXV. See if you can blow thru it while holding the bulb in your hand. Then put bulb in ice. It should shut down.

mk378 on Thu May 24, 2012 5:54 PM User is offline

A good TXV installed backwards will slam shut like that too.

If it's not a complete blockage, the restricted part (which is normally on the high side and thus should be warm) will get cold.

mrpate on Sat May 26, 2012 11:59 AM User is offline

mrpate on Sat May 26, 2012 12:03 PM User is offline

I removed the new expansion valve and it is stuck in the closed position. I even put the thermal bulb in boiling water and was still unable to blow through the valve body. The new valve is out of warranty so it looks like I will have to purchase another new valve.

Thanks for your suggestions---Mark

Dougflas on Sun May 27, 2012 5:44 PM User is offline

Sounds like you lost the charge in the sensing bulb.

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