Coolant valve operation ?

[kenn]

Hello, I'm putting the 350 engine back in my 72 c10 and I checked the vacuum valve to the heater and it is not stopping the coolant flow.

Is the valve suppose to stop the flow completely or not ?

It does have air conditioning.

The vacuum side works fine.
Thanks Kenn.

[Stocker]

I believe that valve is intended to completely block the flow of coolant. The valves sometimes fail, though.... luckily, replacements are available. Another sure-fire "fix" (more a band-aid than a fix) is to put a plumbing ball valve in your heater hose. Just be sure to open the valve before you need the heater/defroster.

[kenn]

Thanks, I will buy a new one as this one is original. I just wanted to make sure I needed a new one.
Kenn

[PbFut]

It is a normally open valve unless ac triggers it to close. The intent is to allow for some bypass of the tstat to avoid hot spots in the heads during warm up until the tstat opens some. Not a issue in summer as the stat opens pretty fast in warm weather so ok if ac is on at start up in summer. Not a good idea use a ball valve though it is often done.

[kenn]

Thanks again, I'll bet my A.C.will be cooler as it wasn't very cold.

[PbFut]

Yes but I believe the heater core is out of the AC air flow path unless you have the lower lever slid to the right off the ac position. The lower lever, using a cable, activates a flapper in the air flow path directing to the heater core or the AC evaporator. I had my evaporator out the other day and was observing the functional process of the system to better understand it's intended engineering and observed this functionality. Seeing this makes better sense on what the levers do. The middle lever is attached to an electric switch in series with the fan switch and goes to the AC compressor. There is a white line on the AC panel between the upper and middle lever. Moving the middle lever into that white line area is where the AC compressor trigger is. Left, the compressor is remains engaged. Right the compressor is off. Middle lever also selects vents. The heater core water valve is activated by the upper lever. It is on the same vacuum circuit as the inside outside flapper actuator and the actuator in the passenger footwell. All 3 actuators move at the same time. It seems that the water to the heater core is only turned off when the upper lever is to the left of the line between inside and outside air. I can not say this 100% correct to original design. 50 year old truck, it is possible someone has mixed up or combined vacuum hoses, but it is the way my system works. (72 GMC)
I have sean comments on some systems cooling so well they have to stop to warm up. Simply sliding the lower lever left with the AC in the outside air position will flow water to the core. Siding the bottom lever right a small amount will introduce a mix of heated air with the AC air and provide a more comfortable output.

[BROWN 70]

x2 post 2. this is what I did. works great. I must have replaced 2 or 3 of the stock ones since I,ve owned my truck. chuck

[kenn]

Hello, RockAuto had it to my house in 2 days with cheapest shipping.
Kenn