1994 silverado...My heater digital screen that shows the position of heater controls has for the last 10 years gone bonkers only when the ambient temperature is about 60 degrees or less ... the icons all come on at once blinking on and off until the cab warms up to approx 70 degrees or more..heater works fine I just press the fan button and temperature button and kinda guess to where its set...now when I turn it off I hear a constant thumping noise from the heater box for about 20 seconds and stops...any one out there run across this??

 

The display problem is most likely due to weak electrical connections. First inspect the cabin fuse panel and make sure all fuses are fully seated.

Second remove the panel and inspect the electrical connections for looseness, corrosion or other damage. Clean and repair as necessary.

3rd, the control panel could have cold solder joints. If you’re comfortable with a soldering iron, you can disassemble the panel and repair the joints by heating them and adding a little fresh solder.

The thumping is due to one of the control actuators having a stripped or broken gear. You can determine which one by disconnecting them one at a time to see which one makes the noise stop.

The mode actuator is on the left end of the HVAC box, near the gas pedal.

The temperature actuator is near the center of the HVAC box, somewhere above the transmission tunnel. It should be visible from below the dash once any insulator panels have been removed.

I posted a write up on these actuators a while ago. The ones I used for the write up were off of post 2000 model trucks but the actuators on your truck will operate on the same principles.

https://chevroletforum.com/forum/gen...urious-102672/

 

Gumby22...Thanks for the reply...your info will help bigtime..really didnt know where to begin..lost my manual in a fire while back..was about to pull heater,...youve givin me hope .. thanks..

 

update...pulled the control panel & disconnected the plug..plugged it back in... it was about 40 degrees this morning and problem solved with the crazy display screen..works like it should...Seems like the actuator above tranny tunnel crammed up by the fire wall is the bad one, thats where I can feel the thumping...getting that out looks like a riot...may be a while before I go after that..