heater control valve

JD1964

Greasemonkey
Dec 31, 2014
179
63
On a 79 Malibu, what is the process for the function of the heater control valve? In other words, does the valve close, or open when it gets a vacuum signal? Also, on what settings at the head unit control does the vacuum signal get delivered or removed from the heater control valve?

I'm going through the HVAC controls and fixing everything during the engine swap project and deciding what type of heater control valve to get. I dont what the stock one since it appears to have a threaded fitting on one end which I cant use in my non stock application. It will be heat only and AC delete but I'd still like to prevent hot coolant running through the heater core in the summer months. i know I could use a manual shut off and I have not yet ruled that out. However, the head unit and vacuum controls are working as far as I can see so why not just use a vacuum controlled valve.
 

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
5,620
113
This might work. The heater control valve should close when you go to "Cold" on the lever, anything off of cold will release the vacuum, and in any temp position when you're in "MAX".

 
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JD1964

Greasemonkey
Thread starter
Dec 31, 2014
179
63
This might work. The heater control valve should close when you go to "Cold" on the lever, anything off of cold will release the vacuum, and in any temp position when you're in "MAX".

That part is exactly one of the options I'm considering. So the stock G body system "closes" the control valve when vacuum is applied? Correct?

I'm trying to make sure I order the correct valve because I think both types are made. Some close the valve with vacuum, others open the valve with vacuum.
 

JD1964

Greasemonkey
Thread starter
Dec 31, 2014
179
63
Just found this too which is helpful. So now I just need to confirm the 79 Malibu designed action. Vacuum applies to opening or closing of the valve?

Question:
What’s the difference between hv1021c and hv1022c
Answer:
1021c is closed with no vacuum on, 1022c is open with no vacuum on.
By Mike H on October 19, 2018
 

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
5,620
113
Cool. You want open with no vacuum. Good thing you asked because I surely didn't realize they had different "options" so to speak. I usually just deal with NOS GM junk.

Here's a diagram of what's going on...I think it applies to 79 Malibu/Monte/El Camino.

Note- water valve switch (2 port disc valve operated by hot/cold lever) only applies vacuum to close the heater valve from the violet line when lever is in COLD when the top lever is in anything other than MAX. In other words, Positions 1, 3, 4, 5, 6, and 7.

The Function Control Switch (7 port disc valve operated by top mode lever) when placed in the "2" position for MAX also applies vacuum from the violet line, albeit a different route through the valve on the back of the HVAC control unit. When in Max, it doesn't matter what you do with the temperature control lever, you'll always get vacuum to the cutoff valve.

hvac-jpg.3918
 
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