1993 C4 No Heat
Thread Starter
Heel & Toe
Joined: Jun 2009
Posts: 23
Likes: 0
1993 C4 No Heat
Anyone have suggestions on what to check to get heat in this vette?
These are the things I've checked...
> Hoses are hot to heater core.
> Fan and heater control module are working.
> AC works fine but when we raise the temp no heat comes out.
> All vents do open when buttons are pressed for that particular one.
> I highly think it is a heat core just because I'm the original owner and this Vette only has 60,000 miles on it. Coolant has ben flushed many times since I've owned it.
I did read about someone saying something about a "Heater Valve" not working. But can't seem to find where that is in the GM manual I have. Is there another name that may full under?
Any suggestions would be appreciated.
These are the things I've checked...
> Hoses are hot to heater core.
> Fan and heater control module are working.
> AC works fine but when we raise the temp no heat comes out.
> All vents do open when buttons are pressed for that particular one.
> I highly think it is a heat core just because I'm the original owner and this Vette only has 60,000 miles on it. Coolant has ben flushed many times since I've owned it.
I did read about someone saying something about a "Heater Valve" not working. But can't seem to find where that is in the GM manual I have. Is there another name that may full under?
Any suggestions would be appreciated.
Advanced
Joined: Sep 2010
Posts: 86
Likes: 4
From: Hampstead NC
Anyone have suggestions on what to check to get heat in this vette?
These are the things I've checked...
> Hoses are hot to heater core.
> Fan and heater control module are working.
> AC works fine but when we raise the temp no heat comes out.
> All vents do open when buttons are pressed for that particular one.
> I highly think it is a heat core just because I'm the original owner and this Vette only has 60,000 miles on it. Coolant has ben flushed many times since I've owned it.
I did read about someone saying something about a "Heater Valve" not working. But can't seem to find where that is in the GM manual I have. Is there another name that may full under?
Any suggestions would be appreciated.
These are the things I've checked...
> Hoses are hot to heater core.
> Fan and heater control module are working.
> AC works fine but when we raise the temp no heat comes out.
> All vents do open when buttons are pressed for that particular one.
> I highly think it is a heat core just because I'm the original owner and this Vette only has 60,000 miles on it. Coolant has ben flushed many times since I've owned it.
I did read about someone saying something about a "Heater Valve" not working. But can't seem to find where that is in the GM manual I have. Is there another name that may full under?
Any suggestions would be appreciated.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
GM calls it a "temperature door". Most people call it a "blend door" or "temperature blend door". It changes the ratio of cold to hot air that flows through the HVAC ducts, which is where the "blend" part comes from.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
If you check the hoses after driving and the hood closed you will not get a valid test by grabbing the hose. Even a small flow of water and ambient heat will heat the hose up but will not get heat into the cabin.
There is no heater valve but only a flow restrictor. The water always flows thru the core.
I like to start the engine from cold. Before the stat opens the heater hoses should begin to get hot. They should get pretty hot before the stat opens and be the same temperature. As the stat opens and the radiator hoses get hot, the heater hoses should be as hot as your bottom hose. If all are the same temperature, then there is probably no flow restriction.
You can also remove the blower module form the top side of the evaporator and look inside to see the blend door. Set the door to 60 and then 90 and see if the door changes positions.
There is no heater valve but only a flow restrictor. The water always flows thru the core.
I like to start the engine from cold. Before the stat opens the heater hoses should begin to get hot. They should get pretty hot before the stat opens and be the same temperature. As the stat opens and the radiator hoses get hot, the heater hoses should be as hot as your bottom hose. If all are the same temperature, then there is probably no flow restriction.
You can also remove the blower module form the top side of the evaporator and look inside to see the blend door. Set the door to 60 and then 90 and see if the door changes positions.
Last edited by pcolt94; Jan 5, 2015 at 04:20 PM.
Racer
Joined: Oct 2014
Posts: 276
Likes: 12
From: DFW Texas
If you check the hoses after driving and the hood closed you will not get a valid test by grabbing the hose. Even a small flow of water and ambient heat will heat the hose up but will not get heat into the cabin.
There is no heater valve but only a flow restrictor. The water always flows thru the core.
You can also remove the blower module form the top side of the evaporator and look inside to see the blend door. Set the door to 60 and then 90 and see if the door changes positions.
There is no heater valve but only a flow restrictor. The water always flows thru the core.
You can also remove the blower module form the top side of the evaporator and look inside to see the blend door. Set the door to 60 and then 90 and see if the door changes positions.
Intermediate
Joined: Oct 2014
Posts: 27
Likes: 3
From: Florida
Common C4 Problem - no or little heat-easy fix
Anyone have suggestions on what to check to get heat in this vette?
These are the things I've checked...
> Hoses are hot to heater core.
> Fan and heater control module are working.
> AC works fine but when we raise the temp no heat comes out.
> All vents do open when buttons are pressed for that particular one.
> I highly think it is a heat core just because I'm the original owner and this Vette only has 60,000 miles on it. Coolant has ben flushed many times since I've owned it.
I did read about someone saying something about a "Heater Valve" not working. But can't seem to find where that is in the GM manual I have. Is there another name that may full under?
Any suggestions would be appreciated.
These are the things I've checked...
> Hoses are hot to heater core.
> Fan and heater control module are working.
> AC works fine but when we raise the temp no heat comes out.
> All vents do open when buttons are pressed for that particular one.
> I highly think it is a heat core just because I'm the original owner and this Vette only has 60,000 miles on it. Coolant has ben flushed many times since I've owned it.
I did read about someone saying something about a "Heater Valve" not working. But can't seem to find where that is in the GM manual I have. Is there another name that may full under?
Any suggestions would be appreciated.
A quick check is provided to you by atgordon yesterday (1/5/15) and other info from Cliff Harris showing this blending damper door. from under the hood, just remove the small plate with a wiring harness at the top of the heater box (he posted a photo) and see if this damper door will move when you change the settings from extreme A/C to full 90 degree heat. If yours is like mine, it will not move and allow air to flow through the heater core and give you heat.
If the damper door is stuck, then look at and probably replace the #51595 elec motor which is inside the car right above your passenger's feet. Look at other posts and mine (john6277) to see how you remove the fuse panel covers to access the knee pad under the dash - be careful as this piece has plastic tabs in the front that are probably quite brittle.
This is really a pretty simple check and fix in less than an careful hour of time. Have fun John
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Thread Starter
Heel & Toe
Joined: Jun 2009
Posts: 23
Likes: 0
Look at Eckler's part #51595 ($100) to see a elec motor for A/C / heater temp control valve. In most modern autos this "blends" the heater core side and A/C side in the heater box to give you the temp air you dialed in.
A quick check is provided to you by atgordon yesterday (1/5/15) and other info from Cliff Harris showing this blending damper door. from under the hood, just remove the small plate with a wiring harness at the top of the heater box (he posted a photo) and see if this damper door will move when you change the settings from extreme A/C to full 90 degree heat. If yours is like mine, it will not move and allow air to flow through the heater core and give you heat.
If the damper door is stuck, then look at and probably replace the #51595 elec motor which is inside the car right above your passenger's feet. Look at other posts and mine (john6277) to see how you remove the fuse panel covers to access the knee pad under the dash - be careful as this piece has plastic tabs in the front that are probably quite brittle.
This is really a pretty simple check and fix in less than an careful hour of time. Have fun John
A quick check is provided to you by atgordon yesterday (1/5/15) and other info from Cliff Harris showing this blending damper door. from under the hood, just remove the small plate with a wiring harness at the top of the heater box (he posted a photo) and see if this damper door will move when you change the settings from extreme A/C to full 90 degree heat. If yours is like mine, it will not move and allow air to flow through the heater core and give you heat.
If the damper door is stuck, then look at and probably replace the #51595 elec motor which is inside the car right above your passenger's feet. Look at other posts and mine (john6277) to see how you remove the fuse panel covers to access the knee pad under the dash - be careful as this piece has plastic tabs in the front that are probably quite brittle.
This is really a pretty simple check and fix in less than an careful hour of time. Have fun John
Turns out the blending door was working fine, then went to flushing the heater core that took care of the problem.
Couldn't believe this was the issue since we flush this system every 4 to 5 years and the corvette only has 60,000 miles on it.
Guess you learn something new all the time.
Thanks for everyones help.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Ok solved the issue.....
Turns out the blending door was working fine, then went to flushing the heater core that took care of the problem.
Couldn't believe this was the issue since we flush this system every 4 to 5 years and the corvette only has 60,000 miles on it.
Guess you learn something new all the time.
Thanks for everyones help.
Turns out the blending door was working fine, then went to flushing the heater core that took care of the problem.
Couldn't believe this was the issue since we flush this system every 4 to 5 years and the corvette only has 60,000 miles on it.
Guess you learn something new all the time.
Thanks for everyones help.
I don't think my car had good care before I got it which may contribute to this condition.
