Heater control valve operation

[E60coyote]

Is the heater control valve supposed to stop the flow of hot water through the heater core completely when heat is set to “cold”?  I rebuilt my heater box and control valve (with Blunttech kit) and I swear when I bench tested and initially installed in the car it did stop the flow.  This was nice because I could let unheated air into the cabin by moving the left climate control to “heat” and the right control on “cold”. It now seems to let some hot water run through the core with this setting. The return heater hose is hot and it blows warm air. I would like to be able to let unheated air through the box.  Is this normal operation?

[Healey3000]

Hi,

 

Have you checked the linkage to see whether the cable has slipped, preventing the valve from moving fully?

[Mike Self]

It's really easy to reinstall the control cable and bellcrank backwards so that the valve is open when the dash control is set at "hot" and vice versa.  Compare with another car or check some pictures on the FAQ to make sure you have it correct.

 

Also, later cars (74-76 IIRC) had heater valves with very small holes drilled in the rotating part of the valve that would allow a tiny flow of water past the valve at all times.  That was to prevent the "stagnant" coolant in the heater core from allowing additives and other crud to precipitate out of the coolant and clog the passages in the core.  That may be what you're noticing.

 

 

mike

[E60coyote]

Yes, I've checked that the valve is moving fully and the cable is not slipping.  Interesting about the hole always allowing flow.  this could be it but I don't think it flowed through when I bench tested it. Perhaps the water pressure in my house wasn't enough. And maybe when I first installed it the outside air coming in was much cooler because the air temp was lower and the engine wasn't up to temp?  I'm just trying to figure out if its working normally before I pull the bugger out.  Not easy with the heater box installed...