sprfrkr

I am troubleshooting some HVAC issues.

I pulled the five leads from the Vacuum Solenoid block to test them individually with my multimeter.

I put the car to "Run" without the engine started and went trhough each of the HVAC vent slider positions and tested each colored lead for voltage. The onlybtwo leads that gave a reading were the green and yellow wires. No other wires produced any voltage as I went through each vent slider position.

I did this with TWO hvac control units. I had an extra from the previous owner.

I would assume all of the leads for the vauum solenoids would be activated at some point along vent selector.

bureau13

Is that a valid test without the engine running? I'm not sure...

Alan

Flap activation is also dependent on the temperature slider setting, the actual mixing motor position the heater core temperature and AC status.

Water Valve - Dependent on temperature selected & internal/external sensors
Defrost/Defog - Dependent on Airflow slider, DEF and microswitch
Footwell - Airflow slider and also dependent on heater core temp & temp setting
Comb Flap - Dependent on temperature selected & internal/external sensors
Recirculate - Dependent on temperature, DEF and AC selections (only a few years have dedicated Recirc slider position)

It is important to understand what the flaps are for to understand the control mechanisms

Alan

Kevin in Atlanta

It is my understanding that the water valve solenoid is dependent on the setting motor. The setting motor is dependent on the temperature selected & internal/external sensors.

Alan

Yes - the mechanism by which the temperature setting and internal & external sensors control the water valve is via the flap mixing/setting motor (so it must be working correctly)... but it is the temp setting and internal/ext temperatures that define the behaviour. I mentioned the motor to indicate that it is involved in the process.

You can test without the car running (with an alternate vacuum source) but it would work much better if the car was already fully warmed up.

Alan

sprfrkr

I see. Ok, I will have to retest everything with the car running and include the temperature slider in the tests.

dr bob

Take a look at the WSM section for the HVAC. There's a "truth table" that tells the condition =s for each to be activated. Your somewhat-random testing for voltage will give you somewhat-random results, I suspect.