Just installed a Classic Auto Air A/C system on my '71 Camaro with LS1. A strange problem has popped up. Before, I had no heater at all, and just had connected heater output to heater return on the water pump. Now, with the heater installed, I have an overheating problem that occurs only when the heater control valve is shut (no circulation of heater coolant). When the valve is opened again, the coolant temperature plummets - even though no air is flowing through the heater core. Close that heater control valve again, and temp immediately climbs back out of sight. Open that valve, and it will drop from 240 to 180 in seconds (my Ron Davis radiator/dual fan setup is very efficient, had no cooling issues whatsoever before the heater install).

Is this some kind of known issue? With forum search busted, I can't tell if anyone else has run into this before ...

Thanks for anyone who can help.

 

having same problem with 2 cars with 5.3 motors.we took thermostats out,,but we
are trying to find correct repair

 

Sorry I can't help, but I have been trying to decide on which a/c set up to get for my 71 camaro, the Classic Auto Air or the Vintage Air? Which compressor are you using with your air? The stock ls1 or the sanden compressor? Did you notch the frame or mount it high? Vintage Air claims the sanden needs to be used because the stock compressor will not last long. Classic Auto Air says I can use the stock compressor or the sanden. Does anybody know the pros and cons between the two companys? Thanks

 

I chose the Classic Auto Air kit because it is a direct fit kit for the 2nd gens. Vintage Air does not make a specific kit for 2nd gens, so you have to "assemble" one from various components.

The kit install was fairly straightforward, we had some issues with it blowing fuses that turned out to be a broken microswitch that was easily replaced. We had to have some A/C lines lengthened because the compressor location is not the same as a first gen SB. The kit seems to be working fine. It is a fairly flexible unit, with control settings for bi-level defrost or dehumidified defrost. One issue with all of these aftermarket kits is that they are all recirculating units - no fresh air. Have to open kick panel vents or crack windows open for fresh air.

I used the Sanden compressor, high mounted on the passenger side using brackets sold by the shop where the install was done, Modern Classics Automotive in Lake Oswego, Oregon, (503) 635-8252. Ask for Steve.

 

Just got a message from Steve at Modern Classics - he suggests that it may be the heater coolant flow that exposes the thermostat to hot coolant to make it open. Blocking that flow would cause the tstat to remain shut. This sounds like it jibes with zz4bronco's experience that removing the tstat fixes the problem.

If this is the case, then just a small amount of heater coolant circulation would fix the problem. I may stick a small diameter H-pipe between the two heater lines, which would allow some coolant to circulate at all times, and see if that does it.

 

I guess I am a bit confused. Is this a problem with the a/c unit? Does the a/c unit block the coolant flow through the heater core when the heater is turned off?

 

Yes. Any heater system which blocks heater coolant flow in the cold temerature setting will have this issue, I believe.

Haven't had time to experiment with an h-pipe yet, am too busy getting the rest of the car ready for track day this weekend.

 

Thanks, let me know when you get a chance if the h-pipe works.

 

Update on this - I put an H-pipe (actually, made one up from 2 tee fittings and a piece of hose) between the two heater lines (before the heater contol valve, of course). This completely cured the overheating problem with the heater valve shut. And the heater itself still works fine - seems to crank out just as much hot air as it did before I put in the H-pipe.

Curious that more folks don't seem to have run into this problem before ...

 

What year engine do you have?