and yet another climate control question
Thread Starter
Drifting
Joined: Aug 2008
Posts: 1,921
Likes: 53
From: Philadelphia Pa
and yet another climate control question
I have an 87 with the ACC with what I believe is the C68 controller. When I get in the car in the morning and having left the controller on "Auto" the prior night, I can get heat out of the heater and into the car. Once I push any other button, the heat disappears not to return until I let the car sit over night. Turning the car off for a few minutes won't do it. It needs to sit over night. I tried a quick fix by replacing the vac check valve located under the distributor but that didn't fix the problem. I'm now thinking that the "computer" on the firewall above the gas peddle may be the issue, those notorious "resisitors". But before I go there, I wanted to ask you guys if you have any other thoughts or recommendations as to what may be causing this particular type of problem.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
What comes out in Auto is determined by the Inside and Outside Air Sensors. If it's dialed in to 72 and it's 60, some heat is normal until the Inside Sensor approaches 72. The opposite is also true. You've got it dialed into 72, the ambient is 50, but the interior is 100 + because it's sat in a parking lot with the sun cooking it. In that situation, it should be at full a/c, and then once it's cooled, switch back to something less.
You need to look at it a little closer. When you get the heat, does it eventually switch over to a/c or something close to what you've dialed in? Put a digital thermometer at the Inside Sensor - what the air temp when you start it? What's ambient?
You need to look at it a little closer. When you get the heat, does it eventually switch over to a/c or something close to what you've dialed in? Put a digital thermometer at the Inside Sensor - what the air temp when you start it? What's ambient?
Thread Starter
Drifting
Joined: Aug 2008
Posts: 1,921
Likes: 53
From: Philadelphia Pa
SunCr, thank you for the reply. I haven't done the thermometer thing yet, but I should also have stated the following:
Once I push any button other than "Auto", I can no longer get any heat out of the heater (even pushing the "heat" only button merely diverts the non-heated air to the floor).
If I run the settings from 60*to 90*, I get nothing but what feels like cold or ambient air, definitely not hot. This has been going on for the last year and a half, during that time, the ambient air has been from about 20* to 95*. I have tried running the setting from min to max under those temperatures with no luck. I have to wait until the next day to get heat. Does this additional info help at all?
Where is the inside sensor located?
a hypothetical: If the inside air is 85* and the outside air is 85*, if I set the temperature setting to 90*, will the heat come on?
Steve
Once I push any button other than "Auto", I can no longer get any heat out of the heater (even pushing the "heat" only button merely diverts the non-heated air to the floor).
If I run the settings from 60*to 90*, I get nothing but what feels like cold or ambient air, definitely not hot. This has been going on for the last year and a half, during that time, the ambient air has been from about 20* to 95*. I have tried running the setting from min to max under those temperatures with no luck. I have to wait until the next day to get heat. Does this additional info help at all?
Where is the inside sensor located?
a hypothetical: If the inside air is 85* and the outside air is 85*, if I set the temperature setting to 90*, will the heat come on?
Steve
Last edited by Steve59; Aug 11, 2013 at 02:00 PM.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Sounds like your temp door doesn't work. Remove the Blower Module on the left side of the Evaporator Case and look inside. Have someone hit the 60 and then the 90 and the door should move. If not, see if it moves when you (gently) push it with a screwdriver. Door problems on these years are usually the plastic piece connecting the motor to the door linkage. Access is from the the passenger side after you remove the Hush Panel.
Inside air Sensor is under small 1 X 1 grate mounted under the middle roof support (assuming you have a Coupe). There are codes for an open or short, but that would be indicated by a Flashing LED under the Outside Air Temp Readout on the Controls. Outside Air is down Low on the Radiator Shroud. It also has open and short codes, but if your outside air temp reads 20 degrees above ambient after you've sat in traffic for 30 minutes on a 70 degree day, it's probably working. The location of the Sensor makes it horribly inaccurate without air flow.
60 or 90 overrides the Inside and Outside Sensor Inputs so it should give you full cool or full heat with Max Blower.
Inside air Sensor is under small 1 X 1 grate mounted under the middle roof support (assuming you have a Coupe). There are codes for an open or short, but that would be indicated by a Flashing LED under the Outside Air Temp Readout on the Controls. Outside Air is down Low on the Radiator Shroud. It also has open and short codes, but if your outside air temp reads 20 degrees above ambient after you've sat in traffic for 30 minutes on a 70 degree day, it's probably working. The location of the Sensor makes it horribly inaccurate without air flow.
60 or 90 overrides the Inside and Outside Sensor Inputs so it should give you full cool or full heat with Max Blower.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Here's a link to a thread on how to get into C68 diagnostic mode:
http://forums.corvetteforum.com/c4-t...stic-mode.html
Just for reference, I took some pictures through the evaporator housing opening of the blend door.
This what it looks like in the 60°F position (it's the rusty thing -- the evaporator is on the far left -- the dark area on the right is the opening into the HVAC ducts):
This is the 90°F position (exposing the heater core):
http://forums.corvetteforum.com/c4-t...stic-mode.html
Just for reference, I took some pictures through the evaporator housing opening of the blend door.
This what it looks like in the 60°F position (it's the rusty thing -- the evaporator is on the far left -- the dark area on the right is the opening into the HVAC ducts):
This is the 90°F position (exposing the heater core):
Last edited by Cliff Harris; Aug 12, 2013 at 03:00 AM.
