Finally!!!!!!!!!!!! A.C. working fine, (sort of) after replacing all of the componants except for the evaporator. Now to explain "SORT OF". It's cooling down to 40 degrees. However, thats BEFORE the engine reaches "normal" operating temperature. If I'm on the hyway it cools at arond 58 degrees. In traffic it will rise as high as 65 degrees. HELP. I know there are some issues of heat transfer from the engine compartment to the cab. Hoping thats the prob. Anyone ever actually mount a "helper" fan in front of the condenser as I have had suggested by a few people. Looking at the area in front of it, I'm seeing NO room to mount anything in front of it. (condenser). When you open the hood, the nose of it is almost right up against the condenser. Any advise would be appreciated.

 

Do you have enough freon in the system? I havent worked on corvette AC, but on modern cars ive seen temps down to 18 degrees with a temp gun. If the condenser cant stay cool that will have an affect on performance. It is basicly a heat exchanger, pulling heat out of the car and getting rid of it in the condenser. Newer 134 cars run about 30-35 psi on the low side. If you have upgraded all your hoses and seals I would think you could run the same. Not an expert, but thats my .02 hope it helps

 

Yes, hoses as well as evry other part except for the evaperator have been replaced. @ 75degree ambient temp the high side pressure was 22o, and the low side was 30

 

Check the weather stripping on the rear of the hood that seals to the cowling. If any hot air from the engine leaks into the cowling area, it will get into the duct work. It sounds like this could be the problem since it starts out cold and then warms up as the engine does.

 

i just installed an a/c in a 70 using a vir eliminator( it was a oem unit from a 76). i have a dewitts rad with spals. there was a huge area on all sides of the condensor that allowed air to bypass the condensor, so i packed foam pipe wrap from home depot all around the condensor to force all the air the fans draw thru the condensor. it must have lowered the temp at the output at least 30*. i'm not sure as to what effect it will have on the engine temp, as the car is not drivable yet.
jeff

 

First lets examine your problem. You say that initially, before the engine heats up, the AC cools to 40 degrees. Once the engine is warm and at highway speeds the performance drops. Lets look at a few facts.

The temp of the radiator should have no effect on the condensor performance since air hits the condensor before it goes in to the radiator. If anything the engine would run at a higher temp since the air passing through the condensor is warmer than ambient temperature. Just make sure your fan shroud (you do have one right?) is installed and sealed correctly to the radiator and the fan (engine driven or electric) is working properly.

Now, given the above, the difference between cold performance and hot performance is probably the temp of the air entering the system. This can be controlled in three ways.

Make sure you have a hot water shut off valve in the heater line to prevent the hot heater core from effecting the temperature of the air entering and coming out of the system. You can get valves at home depot and install nipples of the correct size for the heater hose to cure this problem. If your car came stock with a heater shutoff valve make sure its working properly.

Next check to make sure you are not drawing hot air in the system. This is usually caused by hot air, passing over the exhaust, being drawn in to the system through the air plenum behind the passenger side fender next to the door jam. To cure this problem look at my tech tip on eliminating cockpit heat. Here's the link

https://www.corvetteforum.com/techti...=241&TopicID=3

Finally, make sure there are no air leaks in the cockpit. Look at the firewall and make sure anything passing through it is sealed. Make sure all grommets are in place. Make sure you have a foam collar between the bellhousing of the tranny and the body to prevent engine heat from passing down the tranny tunnel. Make sure the shifter boot that seals the shifter to the body (not the leather one, the one underneath) is not ripped and seals correctly. And make sure that your weatherstripping is installed and working correctly.

If you follow these three steps I'm betting that the difference in performance between hot engine and cold will be minimal.

Good luck.

 

i would double check your evaporator box is sealed...this is a problem i had for a long time...

 

Could the evaporator be freezing up? Do this:

Once the AC starts blowing hot, turn it off for atleast 5 minutes but continue driving the car. Turn it back on and see what happens. If it starts blowing cold again you have evep freezing.

 

I'm not sure I agree with this statement...if the radiator is running too hot it will not cool the condenser efficently. Even though the air passes through the condenser first, the airflow is lower in traffic where he is having most of his problems.

Squirrelguy, just one more thing to consider, check to see if there is any dirt or other crap between your radiator and condenser. When I replaced my radiaor it was pretty dirty and this can also effect the cooling eficently of your condenser. Regardless you may want to try to flush the exterior fins of the radiator and / or condenser.

 

Thanks much for taking the time to give such a thorough answer. I will try all of the above and hope this helps. Yes I do have a fan shroud and it is bolted in place very well.
I will check the web site you linked shortly. Thanks again.

 

Thanks for your responce. I've replaced the condenser and at that time cleaned out a lot of debris from in between it and the radiator. I think my next job will be to replace the radiator anyway, since in traffic the engine temp. with the A.C. on, runs hot. There were many repair spots on this radiator anyway which tells me its probably on its last leg anyway. This along with all the suggestions of blocking out hot air from the engine compartment should do the trick. Thanks to all!!!!!!!!!!!!!!

 

Best possibility for your problem is leakage of outside/engine area air into the A/C system ducting. Lots of possibilities here....inlet cowling diverter, intake air duct seals, rear hood seal bad and allowing engine heat to come in..... you get the idea. If all seals are good and A/C ducting is working properly, then the freezing up of the evaporator is a possibility. You could have too much refrigerant in the system or the intake air is not flowing freely through the evap box and ducting. Evap freeze-up is NOT a good thing...lots of stress on the system.

 

Thanks for your responce. Tried the test that "zwede" (above) suggested, and there appears to be no freeze up with the evaperator. Will go thru all the checks of possible heat transfer from engine compartment to cab one at a time. Thanks again. Oh, judging by the numbers the A.C. shop relayed to me when they charged it up, I'm hopefull that there is not toomuch freon in there. At 75 degrees ambient temp. the highside was at 220, the low side was 30. If that does not seem right for a converted R12 to 134 system, feel free to let me know.