Different HVAC Defroster Issue
Thread Starter
7th Gear
Joined: Feb 2023
Posts: 7
Likes: 1
From: Las Vegas, NV
Different HVAC Defroster Issue
Purchased a 1991 Corvette as a project car and tackling the A/C.
We have all seen and read about the issue with A/C cool air coming out the defroster, but I have come across something different.
I thought I had the usual vacuum issue, but I have finally narrowed it down and want to see if someone else has the issue.
My question is if anyone has run across this issue and/or solution?
We have all seen and read about the issue with A/C cool air coming out the defroster, but I have come across something different.
I thought I had the usual vacuum issue, but I have finally narrowed it down and want to see if someone else has the issue.
- Cool air coming out of the defroster and not the front vents.
- Tested the vacuum line under the passenger side, only getting 5".
- Replaced tee on engine.
- Tested the vacuum under passenger side again, and still only getting 5", so I capped the tee to the cruise control and now I am getting 20" (I will deal with the leak on the cc side later)
- Cool air still coming out of the defroster and not the front vents.
- Being the age of the car (1991), I just had Batee rebuild the head and controller.
- Still had cool air coming out the defroster and not the front vents
- Tore the dash off and tested the tan vacuum line at the defroster actuator controller and getting 20" vacuum when in A/C mode.
- If I manually help stroke the actuator in A/C mode, the damper stays open. (From that I assume no leak in the actuator diaphragm.)
- I see some rust on the defroster blade outside and at this point I think the damper is rusty or dirty and the actuator does not have the strength to stoke the damper blade.
- Pulling out the defroster box or actuator requires full removal of the dash, as it is buried.
- My next attempt is to try and lube it and see if I can free it up a little. (I will give my results if it resolves the issue.)
My question is if anyone has run across this issue and/or solution?
Last edited by Ruby_91_C4; Oct 15, 2023 at 01:45 PM.
Thread Starter
7th Gear
Joined: Feb 2023
Posts: 7
Likes: 1
From: Las Vegas, NV
Update
I Tried brushing rust of the exposed metal parts and sprayed all joint with dry lubricant silicone
Kept assisting the actuator to work it in
It stays open, but will not initiate the start of the stroke.
At this point I have a bad feeling it is the actuator.
No write-ups or videos online to show how to replace.
Fortunately, I have the dash top off, but it sure looks like it requires, pulling the HVAC duct to get to it and that is a PITA
At this point I put a spacer using two threaded 1/2" couplings that are the right length to put under the damper arm and force it to stay open as I need A/C more than I do a defroster
I Tried brushing rust of the exposed metal parts and sprayed all joint with dry lubricant silicone
Kept assisting the actuator to work it in
It stays open, but will not initiate the start of the stroke.
At this point I have a bad feeling it is the actuator.
No write-ups or videos online to show how to replace.
Fortunately, I have the dash top off, but it sure looks like it requires, pulling the HVAC duct to get to it and that is a PITA
At this point I put a spacer using two threaded 1/2" couplings that are the right length to put under the damper arm and force it to stay open as I need A/C more than I do a defroster
Last edited by Ruby_91_C4; Oct 16, 2023 at 11:39 AM.
