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Unable to Charge System

69-er on Sat April 23, 2011 4:11 PM User is offlineView users profile

Year: 1968
Make: Pontiac
Model: Firebird
Engine Size: 400
Refrigerant Type: R12
Ambient Temp: 80
Pressure Low: 85Static
Pressure High: 85Static
Country of Origin: United States

I am trying to charge a 68 Firebird with a factory stock R12 system. During the mechanical restoration I did, the entire AC system was disassembled. Has a new, rebuilt compressor and a new receiver. All lines and components were flushed. System holds vacuum.

When I try to charge it, I can only get 7 ounces to go in. The cylinder is not cold, it's in a bath of hot water. The pressure in both low and high side is 85 PSI at 80 degrees ambient with engine not running. Pressures do not change with engine running and compressor clutch engaged. I confirmed that both schraders are being opened by the hose fittings. I even tried to charge directly from the cylinder to the low and then the high side, nothing, no flow.

It acts like there is only 10% of the system's volume available to charge. I can't believe there would be a blockage, in fact, there would have to be two to isolate the rest of the system. How can that be possible? I don't see how I could have assembled the system incorrectly. Everything pretty much falls into place.

I am totally flabbergasted and puzzled on this! Please help!

Larry

Edited: Sat April 23, 2011 at 4:35 PM by 69-er

Dougflas on Sat April 23, 2011 5:29 PM User is offline

If you have the refrigerant in hot water, the static pressure of R12 will be higher than 85psi. Did you open the valve on the refrigerant?

69-er on Sat April 23, 2011 11:40 PM User is offlineView users profile

I didn't use my IR thermometer on the cylinder, but the water was room temp by the time I got around to charging it. Yes, the valve was open. The gauges also read 85 lbs at the tank with the gauges being disconnected from the system.

mk378 on Sun April 24, 2011 2:52 AM User is offline

Pressure not changing with compressor engaged is a problem. Are there isolation valves on the compressor?

bohica2xo on Sun April 24, 2011 1:30 PM User is offline

A factory system on a '68 Firebird will have an A6 compressor. No isolation valves on that system.

If the compressor clutch is engaged & the pump shaft is turning... you got a bum rebuild. How much & what type of oil is in the sump on the A6?

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

69-er on Sun April 24, 2011 3:04 PM User is offlineView users profile

I can't remember off the top of my head how much oil is in the system, but I used the amount the specs called for. I used mineral oil.

Update: I've been disassembling the system. On the POA valve, should I be able to blow through it? I can detect an extremely small flow coming out of the outlet.

69-er on Sun April 24, 2011 4:16 PM User is offlineView users profile

UPDATE 2:

I didn't want to do this, but with the POA valve removed, I applied shop air to the outlet of the evaporator. Air flowed easily through the system out through the compressor manifold's pressure port. My shop air is going through a desiccant dryer system so I feel confident it didn't overload the system with moisture.

Other than the POA not being able to flow, the rest of the system must be OK. Now I just need to determine if the compressor is OK.

Dougflas on Sun April 24, 2011 5:25 PM User is offline

there is a procedure on this site for testing the POA off vehicle

http://www.autoacforum.com/messageview.cfm?catid=20&threadid=16311


Edited: Sun April 24, 2011 at 5:28 PM by Dougflas

bohica2xo on Sun April 24, 2011 6:27 PM User is offline

Oil "in the system" - or in the sump on the compressor?

For a compressor function test, you can do the bench test for vacuum outlined in the Compressor Flushing tip.

If it won't pull a vacuum, then it will not pump either.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

69-er on Mon April 25, 2011 2:39 PM User is offlineView users profile

UPDATE 3:

I got it to charge! I guess a little innexperience and impatience got the best of me.

After finding nothing during a partial teardown/troubleshooting and with another charge attempt only reaching about 7 oz again, I said the hell with it; I cranked the engine and turned on the AC. It seemed to take forever, but I was able to get the full charge in.

As far as the gauges apparently not reading anything, I only ran the compressor for a few seconds as I didn't think there was enough freon in the system to circulate the oil. I'm also questioning myself as I might still had both valves open, which I think would give me the pressures I saw.

I might feel that I have a decent amount of experience in AC systems, (Enough to be dangerous), but only doing once or twice a year has its drawbacks.

Thanks for everbody's help!

Now, on a separate note, I have a few other questions on another post from this project . Hope some experts can help me there too!

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