Heater control valve for A/C truck really needed?

[mcspeed.1]

I tore into the dash of my truck tonight to see just how bad it had been cobbled up over the last 43 years. I must say that I am rather impressed as to how many original parts are still in place. However, there are no vacuum lines attached to anything! As you can guess nothing was working either! I removed the entire heater box inside to get to all the mode doors as they did not seem to be working (fell apart - Weird!) and removed the cables and straightened them. Tested all vacuum components and they all worked !!! Then I went looking for the heater control valve, what a surprise it is nowhere to be found. The question I have is do I really need the darned thing? I realize that it will stop the flow of hot coolant to the heater/A/C box, but is it that much of a difference if i'm not using either? Also, is it normal for the fan switch to only have slow and medium speeds without the A/C running?

[kamikazekyle05]

bump for you, im curious about the heater valve also

[mrein3]

I went old school on mine. I put a ball valve from the hardware store in one of the heater hoses. It is closed now. With temps dropping up here in the north land it is about time to open it up again. I ran the vacuum line that way and capped it off for now.

Some day I'll get around to installing the proper piece.

To directly answer your question, I think you need it more in the summer than winter. In the winter the AC runs to take the moisture out of the air you're blowing around. In the summer all it does is warm up your air conditioned air.

[mcspeed.1]

Good point mrein3. I think I will order the proper piece and set all the stuff back to original.

[LEEVON]

I have ran for years without the vacuum valve, just a $2 gate valve in its place. I just shut it off in the summer. The downside is during moderate weather where the mornings are cooler and afternoons warmer (the exact days I like to drive) you don't have heat unless you feel like opening the valve and shutting it later.

I am returning all of the heat and a/c to original though, even with R12 refrigerant and replacing the vacuum part.

You should have high, med, and low on the fan switch. Cheap/easy to replace...

[mikemileski]

It is my understanding that, over the six year span of these trucks, 67-72, that two different types of heater control valves were used. One is off when there is no vacuum being applied to it and the other is off only when vacuum is being applied. I have a '72 GMC with factory air and my valve needs vacuum to it for it to be off and no water flowing. I have no idea what years or models go with which valve. When I bought my new valve, I could hold it in my hand and blow right through it. The vacuum line leading to it has vacuum applied when the dash lever is in the COLD position. I hooked that line up to it before I installed it and, sure enough, I couldn't blow through it so I knew it was working properly.

Mike Mileski
Tucson, AZ