Air conditioning problems with my 1973
Thread Starter
4th Gear
Joined: Aug 2002
Posts: 4
Likes: 0
From: Moro Il
Air conditioning problems with my 1973
:confused: My air conditioning system evaporator coil freezes up after 10 to 20 minutes of operation. The compressor (original style) checks out good and I recently had a new VIR unit and condensing coil installed. The head pressure checks good and the suction pressure is where the shop manual says it should be (about 30 psig) which I think may be the problem as this gives a 32 deg F coil temperature (condensate freezes at this temperature; poor design?). Does anybody out there have a VIR system that works as it should? Does any body know what I could do to raise the suction pressure above the freezing point and make the system work! Lastly, are there replacement systems I could install to replace this nuisance system! If it makes any difference the car is a 454 cid with automatic transmission. I still run R-12 refrigerant. Any suggestions greatly appreciated!
Racer
Joined: Aug 2001
Posts: 388
Likes: 1
From: Bridgeport CT
Re: Air conditioning problems with my 1973 (senior)
One of the causes of evaporator freeze up is when the air being blown across the cold fins is diminished. With time, the fins of the evaporator core become plugged from leaves and other organic matter that has fallen into the plenum and been sucked up by the blower motor and deposited upon the core's fins. If the evaporator core cannot loose its cold charge fast enough by having warn air blown over the cold fins - it freezes. If your output of cold air coming from the dashboard vents is weak, this is a further indication of a blocked evaporator core. Only remedy is to open the evaporator case and clean it out.
The evaporator core can also freeze if the blower motor craps out. Again no air is moved over the core’s fins to remove the cold charge.
If you continue to run the AC with a frozen evaporator core, the compressor will burn out.
Geoffrey Coenen
NCRS #2473
NCM Lifetime #105
Vettehead #18-1
Retired #1 56, 63, 67, 68, 68, 69, 75, 99 and I want more !
The evaporator core can also freeze if the blower motor craps out. Again no air is moved over the core’s fins to remove the cold charge.
If you continue to run the AC with a frozen evaporator core, the compressor will burn out.
Geoffrey Coenen
NCRS #2473
NCM Lifetime #105
Vettehead #18-1
Retired #1 56, 63, 67, 68, 68, 69, 75, 99 and I want more !
Le Mans Master
Joined: Sep 2000
Posts: 5,635
Likes: 4
From: Orlando Floriduh
Re: Air conditioning problems with my 1973 (senior)
Slightly undercharged will do that.. At 30 psi(R-12) is discharged at about 36-38 deg. into the evapoator. Lower pressure will produce colder temps (under 32 deg.) which will cause moisture condesation to freeze. That principal is is/was used by used car dealers to make the A/C blow "ice cold" when the costomer test drove the car. I realize that bleeding refrigerant is illegal and most car dealers wuld never do anything illegal! :jester :jester
