No Heat -- 1994
Thread Starter
8th Gear
Joined: Oct 2009
Posts: 8
Likes: 0
No Heat -- 1994
I recently purchase a 94 corvette. When setting the automatic (and manual) heat to 90 degrees, the vechicle only blows cool air. Any ideas why i'm not getting any heat? Also, the AC compressor turns on in automatic mode, is this normal? Thanks in advance for your help!
Racer
Joined: Jun 2006
Posts: 408
Likes: 0
From: Elkton MD
No Heat
Either the heater door is stuck, the core is plugged or the ambient air sensor is shot/disconnected. To check the heater door, remove the module on top of the blower housing (passenger side, near the blower) and look with a flashlight to see if the door moves when moving the temp setting from 60 to 90. To flush the core, remove the heater hoses near the block. If you pull them off of the core nipples, it may break the core or solder. Flush forward and backward many times with a little pressure (the core only takes about 15psi in normal life). If the door is OK and the core is clean, the ambient air sensor is likely shot or disconnected. It's on the passenger side of the radiator, down low and sort of in front of the front right tire. There's a connector nearby so replacement is easy. Not too expensive unless you let the dealer do it.
Hope this helps and good luck.
Oh, yea. It's normal for the compressor to run in auto and defrost.
Hope this helps and good luck.
Oh, yea. It's normal for the compressor to run in auto and defrost.
Drifting
Joined: Dec 2003
Posts: 1,493
Likes: 94
From: Westfield MA
Either the heater door is stuck, the core is plugged or the ambient air sensor is shot/disconnected. To check the heater door, remove the module on top of the blower housing (passenger side, near the blower) and look with a flashlight to see if the door moves when moving the temp setting from 60 to 90. To flush the core, remove the heater hoses near the block. If you pull them off of the core nipples, it may break the core or solder. Flush forward and backward many times with a little pressure (the core only takes about 15psi in normal life). If the door is OK and the core is clean, the ambient air sensor is likely shot or disconnected. It's on the passenger side of the radiator, down low and sort of in front of the front right tire. There's a connector nearby so replacement is easy. Not too expensive unless you let the dealer do it.
Hope this helps and good luck.
Oh, yea. It's normal for the compressor to run in auto and defrost.
Hope this helps and good luck.
Oh, yea. It's normal for the compressor to run in auto and defrost.
Mine just required a flush with the hose and now has great heat
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
With IRAraid This is the correct approach to the problem.I just spent a pile of time fixing my HVAC system and acquired a ton of knowledge on diagnosing and repair of it. Lets hope you don’t have to do what I did and the heater core is plugged up.
A quick check of the core health is to feel the temperature of the heater hoses. They should be about the same as the other hoses once the thermostat has open up. Mine initially when I got the car was always cooler no matter when. And now I flush the core almost every year to keep the heat hot.
I would also recommend if it is the core, that you flush your entire system out including dropping the lower radiator hose and doing the best flush you can. If the core is clogging, the heater and entire cooling system is needs some additional TLC.
Thread Starter
8th Gear
Joined: Oct 2009
Posts: 8
Likes: 0
Thanks for all the replies and advice.
The engine temp is warming up around 200 degrees. I flushed the heater core (fluid ran out quickly); did not seemed clogged. When running the on Auto and setting the temp to 90 degrees the system seems to be running the air conditioner....blowing air colder than outside temp.
I'm starting to think i may be a problem with the Heat/AC Control unit. Notice today; i was unable to turn up the temp....start at 75 degrees..tried to push the temp up but would not increase the desired temp. Push the down to decrease the temp it went down only...unable to raise the temp again. Currently went down to 60 degrees without the ability to raise it back to a warmer temperature. Any ideas. Should i start with replacing the AC/Heat control unit in the dash?
Thanks again!!!
The engine temp is warming up around 200 degrees. I flushed the heater core (fluid ran out quickly); did not seemed clogged. When running the on Auto and setting the temp to 90 degrees the system seems to be running the air conditioner....blowing air colder than outside temp.
I'm starting to think i may be a problem with the Heat/AC Control unit. Notice today; i was unable to turn up the temp....start at 75 degrees..tried to push the temp up but would not increase the desired temp. Push the down to decrease the temp it went down only...unable to raise the temp again. Currently went down to 60 degrees without the ability to raise it back to a warmer temperature. Any ideas. Should i start with replacing the AC/Heat control unit in the dash?
Thanks again!!!
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
I guess you have verified the core is not plugged up. Before going any further perform the procedure as IRAraid explained in post 2. It might be a mood point but its best to find out if the door is moving at all. Get all the data you can so you can make the best decisions.
The controller unit in the dash controls the programmer which in turn controls the door motor. You should be able to run the temperature up and down regardless if the programmer is good or bad. On the surface it sound like the controller is not working right.
Other than replacing it right off, it’s a possibility it may have dirty contacts in the controller. I would remove it, dis-assemble it and clean the rubber and circuit board contacts with alcohol. The two circuit cards in side have a multi pin connector, clean that up also. It might be worth the effort rather than spending a few hundred dollars.
The controller unit in the dash controls the programmer which in turn controls the door motor. You should be able to run the temperature up and down regardless if the programmer is good or bad. On the surface it sound like the controller is not working right.
Other than replacing it right off, it’s a possibility it may have dirty contacts in the controller. I would remove it, dis-assemble it and clean the rubber and circuit board contacts with alcohol. The two circuit cards in side have a multi pin connector, clean that up also. It might be worth the effort rather than spending a few hundred dollars.
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3rd Gear
Joined: May 2007
Posts: 3
Likes: 0
I am having the exact problems that you are. When my temp adjustment gets stuck (and it does several times a year) I give the dash a solid whack just above the controller and it fixes it every time (really, I'm not kidding). I've been doing this for several years now. Last winter my heat stopped working also. I was wondering if you ever discovered what your problem was? My problem may be due to whacking the dash but I need to figure something out.
Burning Brakes
Joined: Feb 2009
Posts: 785
Likes: 3
From: Richmond Virginia
I would think if the blend door was sticking or blend door motor was bad it would be seen as a fault. When in the "auto" mode and you try to adjust the temp from cold to hot---are any lights blinking ?
BTW Yes the compressor does run in the auto mode
BTW Yes the compressor does run in the auto mode
Last edited by TWISTERUP; Jan 20, 2010 at 06:38 PM.
Advanced
Joined: Jul 2004
Posts: 87
Likes: 1
Should i start with replacing the AC/Heat control unit in the dash?
No. Start with cleaning the contacts in the head unit by taking it apart. There are a couple of Tech Tips on this. My unit was "sticking" all the time. Cleaned the contacts with a pencil eraser and it works perfectly now. It is pretty easy to take apart and do and WAY more cost effective than getting a new control unit.
No. Start with cleaning the contacts in the head unit by taking it apart. There are a couple of Tech Tips on this. My unit was "sticking" all the time. Cleaned the contacts with a pencil eraser and it works perfectly now. It is pretty easy to take apart and do and WAY more cost effective than getting a new control unit.
Thread Starter
8th Gear
Joined: Oct 2009
Posts: 8
Likes: 0
I ended up replacing the Blend Door actuator. I was able to find good instructions on this forum detailing the unistall and installation of the new actuator. Once, I replaced the actuator the Temperature Controls seem to work correctly.
My guess is by hitting the dash you may have been freeing up the actuator or causing it to make a contact.
Hope the actuator is all you need. This is a fairly easy fix and cost about $60.
My guess is by hitting the dash you may have been freeing up the actuator or causing it to make a contact.
Hope the actuator is all you need. This is a fairly easy fix and cost about $60.
Instructor
Joined: Nov 2000
Posts: 179
Likes: 2
From: Detroit Area
No Heat -- 1994
BFPQDQT, is the blend door the same as the heater door, that IRAraid was talking about in the 2nd post? What made you decide to change the blend door actuator? Did you not see it move when you changed the temp?
Thread Starter
8th Gear
Joined: Oct 2009
Posts: 8
Likes: 0
Hi Indynick,
The blend door and heater door are the same. To deterimine the blend accuator was the problem i check it following the advice from the second post: "To check the heater door, remove the module on top of the blower housing (passenger side, near the blower) and look with a flashlight to see if the door moves when moving the temp setting from 60 to 90.".
Good luck...hoping this solves your problem.
The blend door and heater door are the same. To deterimine the blend accuator was the problem i check it following the advice from the second post: "To check the heater door, remove the module on top of the blower housing (passenger side, near the blower) and look with a flashlight to see if the door moves when moving the temp setting from 60 to 90.".
Good luck...hoping this solves your problem.
