95 tahoe heater core shut off valve problem

[Zack757]

hey guys just a quick question for you. theres a valve on the engine bay side of the firewall connecting to the heater core hoses which is supposed to at some point cut off hot coolant to the core. this valve is actuated by a solenoid that allows vaccume to flow through a tube directly to the valve. my solenoid appeared to be not working but when i unplugged the wires and put a volt meter on em.. no change in voltage no matter what the climate control is set to.

Ive been having trouble with my hvac unit in the dash for example: no change in voltage to recirculation door motor, erratic voltage to blend door motor.
would no voltage to this solenoid be caused by a faulty hvac control unit?
the plug im holding in the pic is what has no voltage

 

[retorq]

It's more then likely the in dash unit, it could be a chaffed wire but since none of that junk works probably not. Perhaps something is unplugged back there??

You can cap those lines safely on a pre-96 block and heads, Vortec heads on an old block needs addressing, the new setups (Vortec) has another bypass loop, if you want you can route directly from the intake to the pump for now and get your AC working the best while you figure that all out. I have a Vortec headed TBI setup, when it starts to get warm out I basically route the intake directly into the pump and bypass the heater core completely ... when I need it I hook it up again. I removed that valve when I did the head swap to clean it up ... you may need a few hose adapters if you go that route.

Good luck

 

[Zack757]

i think it probably is the hvac unit i went to the juckyard and got a new one and when i plugged all the wiring in and started the truck the electronic board inside the unit went up in smoke. it was probly just a bad part but im gonna try and get a few more and make sure it doesnt just zap them everytime

 

[Zack757]

heres the board that burned up underneath

 

[retorq]

You probably have a short somewhere ...

 

[knoslf]

You probably have a short somewhere ...

I knmow this is a late thread but my hvac was bad too and I still dont haVE HEAT, IT SUCKS THAT OUR HVAC UNITS HAVE AN OPEN MOTHERBOARD BEHIND THE(pardon the caps) dash and I put tape on mine to keep other wires from touching it.