Hi All!
I've got my HVAC (no power) problem narrowed down to where when I turn the key to run, my HVAC controls work. When I start the vehicle, my HVAC power cuts out. I'm thinking this is an ignition switch problem. Does my ignition switch have ground wires running to my junction block HVAC relays?

Any thoughts. And thanks for your time.

 

Is it possible that it is sticking and not returning to the run position and is between start and run. Have seen that many times before.

 

Thanks for the heads up Tizzy1.
This is what I could find. I took the shrouds off the steering column and checked my plug- ins for the ignition switch. All seem good. I also found a 2 pin plug-in directly beneath the lock cylinder. I disconnected that and the neg. battery cable overnight. The lock cylinder has almost no wiggle between stations. I put all back the next day, let the modules communicate, and my HVAC was working after starting.

But, it poored rain and knocked my HVAC out again. Just like the weather that started this whole problem. I need to know what the rain gets into and what needs extra weather proofing in my engine compartment. Thanks for any thoughts.

 

Might be inside. Check the large connector down by the ebrake pedal

 

My connectors look good. All I know for sure is if I disconnect the battery overnight, my HVAC circuit board works. When it rains, it goes out. My van has been parked outside for 13 years and my seals everywhere outside the van are dry rotted. I'm also rusted thru on the driver side column over my spring/shock absorber.
Any thoughts would be truly appreciated!

 

Need to figure out what your missing when it doesn't work. Not to tough, only has key on power and ground. I believe there is a blue, 21 pin connector on the rear of the controls. Pin 10 is the ignition power, brown with a pink tracer, and pin 21 is the ground, black with a light green tracer. When you figure out which you are missing, then we can back trace it. Or is it the blower motor that doesn't work?

 

Thanks, Tizzy1
I needed to educate myself about this pesky problem. Bought a multimeter, took my entire HVAC control head apart, cleaned it all up and re-installed in my caravan.
Here,s what I found: I checked the continuity between pin 10 and pin 21 before I
re-installed and got 28.7 Megomhs on my autorange multimeter. Upon install I found
rear wipe and defrost working, but when I tried to change the mode doors the relays were clicking fast and mode stayed the same. This was a dry night and I think it will stop functioning when it rains again due to the high resistance. My question is with that high resistance is my HVAC control head fried or should I keep looking?
Thanks for your time.

 

shouldn't have continuity through the control head. What your checking for is power and ground. Meter on volts, black lead attached to good ground and key on, should have 12 v to pin 10 on the connector. Then change to ohms and probe pin 21 of the connector and you should have below 10 ohms. But if some things work and others don't, probably not a power and ground issue.