heater control valve

[JD1964]

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]

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".

Amazon.com: Universal Air Conditioner HV 1021C HVAC Heater Control Valve: Automotive

Buy Universal Air Conditioner HV 1021C HVAC Heater Control Valve: Heater Control Valves - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

 

[JD1964]

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".

Amazon.com: Universal Air Conditioner HV 1021C HVAC Heater Control Valve: Automotive

Buy Universal Air Conditioner HV 1021C HVAC Heater Control Valve: Heater Control Valves - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

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]

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]

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.

 

[JD1964]

On the heater control valve I wound up going with a bypass type. With this as the valve cuts off flow to the heater core it continues to cycle flow through the loop in the pump which actually moves water through the head. This way as the engine warms up initially heads won’t get hot spots before the thermostat opens. Here’s the valve I used

https://www.amazon.com/dp/B07BW1458R/?tag=gbody-20

Also, those thin plastic vacuum lines were brittle in the area where they come through the firewall under the heater box. They broke off when I was handling them. So, I cut them off near the glove box under the dash and replaced the removed sections with silicone vacuum lines. The 1/8” id line I got from Amazon fit snug over the remaining ends of the factory thin plastic lines. I drilled perfectly sized new holes in the firewall for the new lines and routed them into the engine area. Here’s the silicone line I used. If you need to repair or replace the factory plastic lines, consider this stuff. It’s working perfectly fit me.

https://www.amazon.com/dp/B07FCYTHVB/?tag=gbody-20

 

[airboatgreg]

The valve has vacuum applied and should close only in the Max air position

 

[69hurstolds]

The valve has vacuum applied and should close only in the Max air position

AND also when the temp lever is in COLD. Anything off COLD will align the vacuum to the valve off.