'95 Interior Heater Mystery Problem

[GDGibbons]

Cannot get interior heater to produce air more than slightly warm. Have replaced electronic controller, backflushed core, etc., no help. Problem started suddenly one cold night. Ocassionally cycling the heater on/off produces moments of warn air, then cool again. Mechanic sez there is no valve in the water line, just doors to control air flow in the interior. Any ideas? (I am over $1000 into this problem, no relief in sight ...) Thanks for any help.

Later: I should have mentioned, the car has automatic heater/AC controls, and as mentioned on another thread, there seem to be a great many was for it to go wrong.

GG

 

[Rabbit]

Have you checked the vacumn valve under the pass/side fuel rail. Worth a look.

 

[John Robinson]

Vacuum check valve

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You can check the valve by removing it and put a piece of hose on one of the nipples and use your finger to block the other one. If you can suck air through the valve it is bad.

Here's the good part The OEM valve is about $7.00 Do not waste your money on the auto parts store version.

This valve controls the cruis and the vacuum to the heater. Let us know what you finally fixes your heater.

 

[air1jpg]

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You can check the valve by removing it and put a piece of hose on one of the nipples and use your finger to block the other one. If you can suck air through the valve it is bad.

Here's the good part The OEM valve is about $7.00 Do not waste your money on the auto parts store version.

This valve controls the cruis and the vacuum to the heater. Let us know what you finally fixes your heater.

With this valve broken, would the cruise control not work either?

 

[John Robinson]

With this valve broken, would the cruise control not work either?

In my case the nipple for the cruise vacuum broke off and the cruise did not work.

Read through this thread it will give you a lot of info especially the post by Junk

http://www.corvetteactioncenter.com/forums/showthread.php?t=98373&highlight=cruise&page=2

 

[GDGibbons]

Still a mystery

Thanks for the tips about the vacuum valve. The mechanic was already on to that (and I verified the part number) and it was not the problem. I have the (cold) car back and the mechanic is still mystified. If I set the setpoint of the automatic heater to 80 degrees, the air that comes out is only slightly warmer than the outside air, one of the two water lines to the heater core is hot, the other barely warm. Have flushed the core, no obstruction in either line or the core.

Does anybody have a block diagram of the cabin heater system? I certainly sounds to me like a malfunctioning water valve in or near the core, but the mechanic swears there is no such valve. Gremlins.

 

[gmjunkie]

Thanks for the tips about the vacuum valve. The mechanic was already on to that (and I verified the part number) and it was not the problem. I have the (cold) car back and the mechanic is still mystified. If I set the setpoint of the automatic heater to 80 degrees, the air that comes out is only slightly warmer than the outside air, one of the two water lines to the heater core is hot, the other barely warm. Have flushed the core, no obstruction in either line or the core.

Does anybody have a block diagram of the cabin heater system? I certainly sounds to me like a malfunctioning water valve in or near the core, but the mechanic swears there is no such valve. Gremlins.

There is no valve on the heater core,The temp is controlled by a blend door in the heater/AC housing!! There is a Plastic clip on the rod of the actuator that can break and cause this problem,but you'll have to remove the Dash Pad to get to it!! Man that Job Inhales a Fat Puppy's Rectal Region!!!!

 

[air1jpg]

There is no valve on the heater core,The temp is controlled by a blend door in the heater/AC housing!! There is a Plastic clip on the rod of the actuator that can break and cause this problem,but you'll have to remove the Dash Pad to get to it!! Man that Job Inhales a Fat Puppy's Rectal Region!!!!

Junk,

I copied the line in quotes from another post about battery drain.

"The drain is from the radio memory, ECM memory and the HVAC Programmer memory if you have the C68 Auto Climate control"

Could the HVAC Programmer memory cause the problems described above if the memory was corupt? Reason I ask is because my vette was having the same symtoms as above until one day the problem seemed to magically disappear after the car was sitting for a number of weeks. The battery did not go dead and the car started ok, but the battery was somewhat drained. :confused

 

[jmccloud]

Heater not hot

Is the air coming out the correct location (defrost, dash, or floor)? If the location is correct, the vacuum control is OK. If the vacuum source or controller is bad, the air flow defaults to defrost/floor and will not come out the dash vents.
But the temperature door could still malfunction, especially if the clip holding the control rod to the door breaks. Remove the module mounted on top of the evaporator housing (under the hood) and check for temperature door movement as the temp is dialed between 90* and 60* (or whatever min and max are). You should be able to readily see the door movement and heater core.
Also, there IS a flow control valve in the line feeding the heater core. It's supposed to keep 'excessive' pressure from blowing out the heater core during high rev. operation. My flow control valve came apart at 5000+ one afternoon and dumped the coolant very quickly - all over the engine compartment. I've read that they can crud up and restrict flow but my sole experience is leakage. The flow control valve is about the size of 1/2 of a $10 roll of quarters, black plastic, located just above the #4 or #6 spark plug. It looks very much like part of the heater hose. Your car should have it (or not if a previous owner discarded it).
Good luck and please post when you find it.

 

[gmjunkie]

Also, there IS a flow control valve in the line feeding the heater core. It's supposed to keep 'excessive' pressure from blowing out the heater core during high rev. operation. My flow control valve came apart at 5000+ one afternoon and dumped the coolant very quickly - all over the engine compartment. I've read that they can crud up and restrict flow but my sole experience is leakage. The flow control valve is about the size of 1/2 of a $10 roll of quarters, black plastic, located just above the #4 or #6 spark plug. It looks very much like part of the heater hose. Your car should have it (or not if a previous owner discarded it).
Good luck and please post when you find it.

Your Right,Now that Im thinking about it I put one on this 94 I have about a year ago!! The 86 in the shop don't have one though,Maybe it's been 86ed!!