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R12 system help for classic car...Please!

Jesse31 on Thu May 01, 2008 4:52 PM User is offline

Year: 1970
Make: Pontiac
Model: Grand Prix
Engine Size: 400
Refrigerant Type: R12
Ambient Temp: 70
Pressure Low: 40
Pressure High: 85
Country of Origin: United States

Please help!... ok here goes...R12 system on 70 GP...was working but had a bad leak...also had a cracked evaporator case so decided to take it completely apart and clean flush....flushed evaporator and condensor with cleaner and then flushed well with water...blew out with compressed air for several hours...replaced the case and put it back together...pressure tested with nitrogen and found several leaks on compressor...installed reman compressor...pressurized again and no leaks...pulled vacuum for ~4 hours...after two days it still was holding vacuum...charged with correct amount of R12 and half of POA was iced up...recovered gas and replaced the expansion valve with another "good" used one...gassed back up and this time had no cooling of POA at all, just an iced line from condensor...WHAT AM I MISSING?...faulty POA?..faulty expansion valve?

mk378 on Thu May 01, 2008 5:16 PM User is offline

Yech - water??? Anyway hope all the water is gone. Next time it is empty pull under vacuum for a very long time, then replace receiver-drier.

You should not have anything getting cold until after the TXV. Icing of lines near the condenser indicates a severe restriction at that point.

Jesse31 on Thu May 01, 2008 5:27 PM User is offline

I forgot to include that I did install a new receiver/dryer.

oznznut on Thu May 01, 2008 6:44 PM User is offline

Just for information, on a properly functioning POA system with a low heat load, such as you described at 70F ambient, the POA outlet side, possibly all the way to the compressor WILL infact frost up, just as you said. The A6 is a powerful compressor with lost of capacity. The TXV is closing down as tail coil temp gets satisfied, and the POA is trying its best to hold the evap pressure to 30 psig. Therefore, the compressor can almost draw a vacuum on the POA outlet. Ergo, frost.

Lost of good info in the archives on your system, or similiar. Just do a search for "POA". And don't let anyone sell you one of those POA "update" kits!! NEVER....NEVER....NEVER

My 1967 Impala SS A6/TXV/POA/R12 will hold 44-46 at idle, and 38-40 at cruise. Was 95 here in Arizona yesterday.

Good luck


iceman2555 on Thu May 01, 2008 6:54 PM User is offlineView users profile

WATER as a flush agent.....once used steam....but took extra care to insure that all the residual moisture was removed.
Freeze up of a component normally occurs adjacent to a severe restriction. Since there is not a sure fire method to insure complete moisture removal using a normal gauge set, simply evacuating the system may not be sufficient to remove possible water accumulations. The use of a micro gauge would be a better indication of complete system purging. The fact that it held a vacuum for an extended period of time does not mean that all of the water was removed. The freeze of the POA could be result of possible moisture in the system.
Where is the frost area on the condenser line. Could be that the drier/filter is restricted and thus the 'iced' line. Please be more specific as to location.
A suggestion would be to have the refrigerant recovered....very expensive to simply blow off....and besides it is an illegal act to do so. Flush the system with a good flush chemical...evap,condenser, hoses. Remove the compressor and drain all lubricants. Add several oz of POE (ester) lubricant to the compressor and rotate by hand a couple dozen times....drain and refill.....repeat as necessary until all the lubricant seems to be the same color and consistency. The do this once more using mineral lubricant to remove as much of the ester lube as possible. Fortunately this system uses the A6 compressor. Simply add the lubricant, rotate and drain thru the drain plug in the bottom of the case.
The evap/condenser/hoses (esp if equipped with mufflers) to insure complete moisture removal. Suggestion would be to use DuraFlushII....evaps good....and seems to do a fairly good job with excessive moisture.
Change the rec/drier.
Recharge the system with the correct amount/type of lubricant. Stay with mineral lube for the R12 system.
Suggest to develop a method to 'air purge' the condenser and evap. Use about 25-40 psi of clean air.....the air should be directed thru a suitable filtration system prior to entering the system components. Keep all the air compressor oil/water/dirt out of the A/C system. Each component should be air purged for at least 25-20 minutes each.
Hopefully the POA valve is useable.
Replace the TXV with a known NEW unit...they are not that expensive.
Already stated...but replace the rec/drier....and no...... one can not evacuate moisture from a saturated desiccant.
During the evac process.....operate the engine....this will increase heat load within the A/C components and aid in 'boil off' of possible remaining moisture. Evacuate the system for a min of 45 minutes to insure as much moisture as possible is removed from the system.
Recharge to correct refrigerant levels and retest.
If possible locate and use a micron gauge to determine proper evac.....a min of 1000 microns....
This system could be severely contaminated with moisture.....have to get it out.....moisture remaining in a R12 system produces an acid that may result is even more serious condemnations........

Low ambient temps may result in possible POA frost...however, the high side freeze up is questionable...esp with the pressure readings indicated

Good luck with the repair.....

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

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