Air conditioned problem
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3rd Gear
Joined: Sep 2011
Posts: 3
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Air conditioned problem
My 1970 factory AC only flows cold air only upon starting the engine cold, then suddendly starts blowing warm air, my compressor and clutch is new , the system is fully loaded with gas. The thumb wheels operate kind of crazy, the left one shuts down the system when its all the way down on the de icing position , can anybody suggest the item that needs to be checked or changed?
Advanced
Joined: Nov 2011
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I believe the 70 model uses a hot water shut off valve. This is designed to shut off hot water flow to your heater core when you are in a/c mode. It is probably either defective or the vacumn supply to the valve has a problem. A quick check would be to block off your heater hose (use a set of vice grips and wrap the hose with a rag) and see if the problem goes away.
Intermediate
Joined: Mar 2007
Posts: 40
Likes: 1
From: Durban KZN
have you checked the heater circuit sounds like the flap seals are gone or the flap is not working. If I remember correctly they use a live core (got that wrong ! 
don't think my 73 had the valve) which means that the heater core always has water running through it and flaps are used to make the air flow though it or around it. If the AC is working properly you could feel the suction tube comming out of the evap - the biger pipe comming out of the firewall under the hood, it should be cold.
hope this helps
don't think my 73 had the valve) which means that the heater core always has water running through it and flaps are used to make the air flow though it or around it. If the AC is working properly you could feel the suction tube comming out of the evap - the biger pipe comming out of the firewall under the hood, it should be cold.hope this helps
Last edited by MarkZ; Feb 24, 2012 at 03:46 PM.
Melting Slicks
Joined: Jul 2009
Posts: 3,264
Likes: 3
From: Vero Beach FL
I believe the 70 model uses a hot water shut off valve. This is designed to shut off hot water flow to your heater core when you are in a/c mode. It is probably either defective or the vacumn supply to the valve has a problem. A quick check would be to block off your heater hose (use a set of vice grips and wrap the hose with a rag) and see if the problem goes away.
Safety Car
Joined: Jun 2004
Posts: 4,354
Likes: 214
From: Beecher Illinois
EXACT same problem I had. Found that the vacuum SWITCH behind the dash(this on 79, not sure if the same for 70)wasn't fully depressing allowing the shutoff valve to close.
Nice cold air til the coolant got hot.
You mention your thumbwheels are kinda crazy.
On the later C3s the temp lever has to be ON COLD for the valve to close. Not close, but ON.
