Corvette's in the Cold
Melting Slicks
Joined: Sep 2008
Posts: 3,138
Likes: 802
From: Espanola New Mexico
The blend door actuators control temperature, but the hvac module also controls the flaps that direct where the air is sent to. The flaps are operated by vacuum which comes from the back of the intake manifold, the vacuum line is a small black plastic line which is brought in with the wire harness.
Thread Starter
Intermediate
Joined: Jun 2025
Posts: 41
Likes: 2
From: Papillion,Ne
HVAC module was the problem!
Glad you were able to do some "field" tests.
Great so we know you don't have any engine coolant issues, the heater core is flowing properly.
More than likely the control system to run air over the heater core for the driver is not working properly.
This is about where my expertise runs out on this topic so I'll leave it for others to comment on next steps.
If you haven't yet, Id follow the reset procedure grinder mentioned. If not some googling will find you the manuals for your car and you an start working through diagnosing there.
Report back if you get stuck! (Or if you solve it to help others in the future
)
Great so we know you don't have any engine coolant issues, the heater core is flowing properly.
More than likely the control system to run air over the heater core for the driver is not working properly.
This is about where my expertise runs out on this topic so I'll leave it for others to comment on next steps.
If you haven't yet, Id follow the reset procedure grinder mentioned. If not some googling will find you the manuals for your car and you an start working through diagnosing there.
Report back if you get stuck! (Or if you solve it to help others in the future
)with the Battery disconnected, I removed the dash then went through a ton of testing based on searches on this forum, Youtube, ChatGPT, the works
First time I reconnected the battery was the only time I saw the actuator reset, after that, nothing
-
- Plug the passenger blend actuator into its harness
- Let it hang or rest on the HVAC box
- Plug in the HVAC control head
- Turn key ON
- Command 60°F → 90°F → 60°F
- Watch the actuator behavior
C5 HVAC recalibration procedure:
- Key ON (engine off)
- Pull HVAC/ECAS fuse #2 for 60 seconds
- Reinstall fuse
- Turn key ON
- Don’t touch anything for 90 seconds
All this time, it looked like the HVAC module was working, at least I saw the lights flicker, like they were resting, etc.
After many scenarios and tests, I believe my refurbished module is faulty
- The unit powers up
- The blower works
- The display works
- But the module does not command any blend or mode actuators
- Recalibration produces no actuator movement
Will keep you posted
Todd
Thread Starter
Intermediate
Joined: Jun 2025
Posts: 41
Likes: 2
From: Papillion,Ne
Getting Close!
Happy New Year to you
Will keep you posted
Todd
