View Full Version : HVAC question... am I on the right track?

09-23-2017, 02:52 PM
As we all know, I bought a basket case for cheap. Winter is coming (cue dramatic GoT theme).

Among the other problems (mostly sorted), the heater core was bypassed. There is a hose leading from a module on the driver's side of the engine compartment (water leaves this module and goes to the egr), it bypasses the heater control valve, and then goes into the outlet pipe on the passenger side of the engine. The entire hose was zip-tied to the factory setup to stay off the engine.

Of course I was thinking either the heater valve was bad, not allowing the A/C to function, or the heater core was bad, and this was an old-school bypass to get down the road. After all, I bought the thing in Phoenix, where A/C is much more important than heat.

Insert a third idea: I found the temp control switch inside is bad. I think the directional control is bad as well, but I am not 100% sure of that yet. The temp valve swings in almost a full circle, from just past the cold to almost back to the cold. I got to thinking that if this were bad, the heater valve might be stuck open, since most vehicles default to heat when there is no power to the circuit.

I undid the bypass, and hooked the hose system back up. I removed the valve and took it to the garden hose to see what position it was in without power. I then hit it with 12v to see if it did anything, and the plunger snapped to the other position with authority. As soon as power was removed, it snapped right back to the start position.

My thoughts are that without power, coolant flows through the heater core, and with power, it does not. As a cheap fix (until I can find, test, and replace the HVAC controls), my idea is simple... hook up the valve output backwards (top to bottom and bottom to top) in order to make it bypass the heater core without power and flow through the heater core with power applied. I am then going to run new wires to the valve, and install a switch in the console for heat. If I get cold, I turn on this switch, it actuates the valve and switches the flow to the heater core, and I can stay warm in the winter.

Am I right in this thinking, or am I setting myself up for disappointment?

09-23-2017, 05:01 PM
You are correct that the valve's "power off" position is to heat the cabin.

I guess my question would be: why not have your new switch close the valve?

That way you would not have to disturb the existing (already disturbed) plumbing.
Power the switch from "Ignition On" or "D+" (best sources are the EK1 terminal strip under the driver's seat.. they're already fused)

By leaving it "power off is heat", you'd be able to use the REST button, too.


09-23-2017, 07:26 PM
By running it as power on for heat, the rest works as well.

I just got done with it, and it was as I expected... I now have a reverse-plumbed heat control and a nice rocker in the center switch bank to operate it. The spinning around and around (yeah, I checked again and that's what it does) temperature switch is now not expected to do anything (since it didn't before) and the A/C works when the switch is off.

09-24-2017, 12:51 AM
Whatever floats your boat heater... :cheers: