Heat and a/c; I got a weird problem here
Thread Starter
Instructor
Joined: Sep 2018
Posts: 165
Likes: 64
From: Lakeville MN
Heat and a/c; I got a weird problem here
So it’s a minor annoyance rather than a problem. And it’s only an issue in the spring when I’m alternating between using heat and air conditioning. This is a 1979 with factory heat and air conditioning, so read carefully here, when I move the temp from cold to hot I get no heat unless I pop the hood and pull the vacuum line from the water shutoff valve and plug it back in. When I move the temp from hot to cold it does what it’s supposed to (cold air). I already have a good schematic of the system and mostly understand how the whole system works, I hooked up a vacuum gauge to the line going to the hot water shutoff valve and verified that vacuum is not being released when the temp control is moved from cold to hot (vacuum holds the valve closed and no coolant goes to the heater core). So what’s the problem? Im guessing it has to be somewhere between the hot water shutoff switch behind the glove box and the actual shutoff valve. This is driving me nuts, any help would be appreciated! And please keep in mind when answering I don’t want to hear anything about bypassing the system or manual shutoff valves, I don’t do bubba work, I’m a bit of a fanatic about fixing things properly and systems working as they were intended. Thanks everyone
Safety Car
Joined: Oct 2007
Posts: 4,383
Likes: 1,755
From: Seattle Area Washington
You have trapped energy (Vacuum) between the HWSV and the switch.
If you look at the switch there are 3 ports, one port is unused and should remain open, that is the exhaust port for that trapped energy...
It could be as simple as a cable adjustment...
If you look at the switch there are 3 ports, one port is unused and should remain open, that is the exhaust port for that trapped energy...
It could be as simple as a cable adjustment...
Race Director
Joined: Nov 2006
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I agree. If you pull the vacuum line off and that releases vacuum and all is fine. Check that vacuum switch on top of the heater box. It's not getting pressed all the way, cable adjustment, or a bug blocked the exhaust. Highly likely.
