more on heater problem
Thread Starter
Racer
Joined: Nov 2003
Posts: 353
Likes: 1
From: Sugar Land, TX
more on heater problem
Well I learned more and discovered my errors in logic. First, flow through the heater core is from the intake manifold to the control valve, heater core and back to the water pump. I had it backwards and should have known better as the bigger hose is always the suction on a pump. Secondly, I tested the vacuum on the old control valve were I determined that vacuum closed the valve. This was wrong, vacuum opens the valve.
I had tested for vacuum coming to the control valve and had vacuum. After more testing, it seems that the vacuum must be intermittent as I do not have vacuum now.
I put a ball valve in place of the control valve as a temporary fix to make sure I had no air in the coolant system, but want to get the control valve back in place.
Can anyone tell me if the vacuum comes directly from the heater control valve in the console, to the fire wall and then to the control valve under the hood? Also, is the vacuum line from the fire wall to the heater control valve one piece or does it extend through the fire wall to the console? I do not want to pull it at the engine side of the fire wall to discover that I have pulled it apart in another location.
Sorry for the ramble, but as always, advanced thanks for any help.
I had tested for vacuum coming to the control valve and had vacuum. After more testing, it seems that the vacuum must be intermittent as I do not have vacuum now.
I put a ball valve in place of the control valve as a temporary fix to make sure I had no air in the coolant system, but want to get the control valve back in place.
Can anyone tell me if the vacuum comes directly from the heater control valve in the console, to the fire wall and then to the control valve under the hood? Also, is the vacuum line from the fire wall to the heater control valve one piece or does it extend through the fire wall to the console? I do not want to pull it at the engine side of the fire wall to discover that I have pulled it apart in another location.
Sorry for the ramble, but as always, advanced thanks for any help.
Burning Brakes
Joined: May 2013
Posts: 789
Likes: 129
From: Los Banos CA
On my 79, the vacuum line runs from the control switch in the console, to a vacuum switch on top of the heater box (behind the glove box), and then thru the firewall to the control valve in the heater hose. The vacuum switch on the heater box switches 'off' when the hot/cold lever is pushed all the way to the 'cold' position, thus preventing any coolant flow thru the heater core.
Thread Starter
Racer
Joined: Nov 2003
Posts: 353
Likes: 1
From: Sugar Land, TX
From my internet search, I think they started putting the vacuum switch on top of the heater box in 1977. 76 did not have the switch so maybe the line runs directly from the console switch to the control valve in the heater lines. Wonder if it is a continuous vacuum line on the 76?
Thread Starter
Racer
Joined: Nov 2003
Posts: 353
Likes: 1
From: Sugar Land, TX
Well folks, I have learned that there are two vacuum switches on the heater control panel. The function wheel (left side) has a multiport switch and the temperature side (right side) has a three port switch. By mistake, I did find that I had intermittent vacuum to the heater control valve and thought that the problem was the three port switch. So I replaced it. After replacing the switch, I still had intermittent vacuum to the control valve, but this is the strange part, on all functions, (A/C, vent, bi-level, heat and defrost) when the temperature wheel is on cold I have vacuum. In other words, the heater control valve would be open. As soon as I turn the wheel to to increase the temperature the vacuum drops to zero or the valve is closed and not allowing water circulation to the heater core, thus no heat.
I have owned the 76 from the beginning so know that vacuum hoses have not been switched.
Any ideas as to what the problem is?
I have owned the 76 from the beginning so know that vacuum hoses have not been switched.
Any ideas as to what the problem is?
