No heat

[LT4John]

This summer I started to get heat though my vents to I installed a shutoff valve in the heater line to shut off the water to the heater core. I removed a connector tube that had an arrow showing the direction of the water flow, see picture. Problem is I did not notice which way the flow was before I remove it. Now with winter starting I opened the valve but got no heat. Thought the valve may not be large enough, so I put back the connector with the arrow pointing to the firewall. Still no heat, maybe it’s in backward, but I can see thought the connector so I don’t think it matters. I checked the vacuum line at the engine head and verified that the valve that controls the vacuum to the heater and cruise by holding a finger over the other small connector and there should not be any air come through the larger discharge fitting.
Both heater lines are hot; I believe that means no air is passing over the heater core cooling off to outlet water.
So now I am under the dash on the passenger side trying to see if the heater door is opening and closing correctly, but can’t find the lever for the door. Does anyone know on a 96 where and how to test the operation of the door for air to pass the heater core?


Thanks in advance,
LT4John

 

[vetteoz]

So now I am under the dash on the passenger side trying to see if the heater door is opening and closing correctly, but can’t find the lever for the door. Does anyone know on a 96 where and how to test the operation of the door for air to pass the heater core?

'89 shown ,'96 can't be too different

If you take the BCM out of the evap core housing in engine bay you can look inside ducting and see if blend door moves
when you change the temp setting on head unit

 

[vetteoz]

Both heater lines are hot; I believe that means no air is passing over the heater core cooling off to outlet water.

Have you pulled the HVAC codes to see if anything is displayed ?

Corvette Action Center Knowledgebase :: 1990 - 1996: HVAC Diagnostic Codes

 

[Schrade]

This summer I started to get heat though my vents to I installed a shutoff valve in the heater line to shut off the water to the heater core. I removed a connector tube that had an arrow showing the direction of the water flow, see picture. Problem is I did not notice which way the flow was before I remove it. Now with winter starting I opened the valve but got no heat. Thought the valve may not be large enough, so I put back the connector with the arrow pointing to the firewall. Still no heat, maybe it’s in backward, but I can see thought the connector so I don’t think it matters. I checked the vacuum line at the engine head and verified that the valve that controls the vacuum to the heater and cruise by holding a finger over the other small connector and there should not be any air come through the larger discharge fitting.
Both heater lines are hot; I believe that means no air is passing over the heater core cooling off to outlet water.
So now I am under the dash on the passenger side trying to see if the heater door is opening and closing correctly, but can’t find the lever for the door. Does anyone know on a 96 where and how to test the operation of the door for air to pass the heater core?
View attachment 1769

Thanks in advance,
LT4John

Could also mean that there's no coolant flow.

And since there WAS an airflow problem, you might have air and coolant flow problems.

Disconnect the core input and return nipples CAREFULLY - THEY CAN CRACK FROM THE CORE BODY - then put the garden hose against either opening, and see what you get. If you can, do the DIS-connects away from the core for safety. Replacing the core ain't a picnic.

If you have GM red coolant, you have core plug - guaranteed.

 

[LT4John]

Thanks Schrade and Vetteoz, I will check out your suggestions.

 

[Schrade]

Heat is over-rated.

Especially since gore invented global warming. Never mind all that snow and ice - it's gettin' warm.

 

[johnnyclassic]

Never heard the word used?

Never heard the word thermostat being mentioned. Maybe pull it out to check it operation?

 

[LT4John]

After I pulled the HVAC codes and found no faults, and I flushed out the system and made sure the core was not blocked I took the BCM out of the evap core housing in engine bay and saw that the blend door was in the wrong position. (Thanks Vetteoz for the info). I move the door by hand and now have heat. The door move easy so it must mean that I have a vacuum leak somewhere. I know the vacuum line at the engine head is okay, must be leaking after that point. I want to check were the vacuum line going into the heater core, but can’t find it. Any one have an idea where I should look or recommendations on a easy way to replace the line?

Regards,
LT4John

 

[Schrade]

Do you get a loping idle? At ALL? Does manipulating ANY controls affect idle? (EXCEPT A/C, which makes a demand for additional STEADY rpm).

If you have a vacuum leak, actively letting air pass, it will make the rpm's lope idle - an antique lawnmower, or a '11 anything still on the dealer's lot.

If the vacuum control is in the 'off' position, it will be harder to detect...

Try to get user 'suncr' or something like that on CF boards. He knows HVAC, and I think he lives near ttechx6.

 

[vetteoz]

The door move easy so it must mean that I have a vacuum leak somewhere. I know the vacuum line at the engine head is okay, must be leaking after that point.

Wrong

Vac does not control blend door (temp ) position; only vent positions
If door moves that freely possibly the link to the ELECTRIC motor is loose or broken ( plastic clip shown in pic above broken )

Get your head under dash and have someone change the heat settings while you see if arm on motor is moving

View from under dash looking up at blend door motor

 

[Schrade]

Nothing that I said is actually 'wrong'.

If I had said:

If the vacuum control to the [heat] is in the 'off' position, it will be harder to detect.

then the statement STILL would be true, even since the heat control is not by vacuum (thanks for answering THAT question).

And the vacuum leak WOULD be harder to detect .

 

[LT4John]

Vetteoz, You are correct, Vac does not control blend door (temp ) position; only vent positions, a ELECTRIC motor controls the door. My 96 is a little different, the motor is connect directly to the door, no linkage. The motor is working and when I change the temp, the motor does move the door. I thought I was all fixed, got heat and life was good. But now I am back to my original problem I had this summer, I get heat on and off when I have the temp set down to 60 degrees. One minute I get cool air, and then it goes hot, then back to cool. I believe I have a logic or connection problem. Any ideas on how to troubleshoot?

 

[boomdriver]

Vetteoz, You are correct, Vac does not control blend door (temp ) position; only vent positions, a ELECTRIC motor controls the door. My 96 is a little different, the motor is connect directly to the door, no linkage. The motor is working and when I change the temp, the motor does move the door. I thought I was all fixed, got heat and life was good. But now I am back to my original problem I had this summer, I get heat on and off when I have the temp set down to 60 degrees. One minute I get cool air, and then it goes hot, then back to cool. I believe I have a logic or connection problem. Any ideas on how to troubleshoot?

Do you have a FSM ?

The book describes the diagnostic display for the elect a/c that works much like flash codes for the engine computer. If it IS a control head issue, those are rebuilt/exchange for about $150.

 

[LT4John]

Not sure what FSM is, but I get no HVAC fault codes.

 

[BigJimZ16]

Not sure what FSM is, but I get no HVAC fault codes.

F - factory
S - service
M - manual

 

[2VettesMike]

A couple of additional thoughts to add...

Try removing the HVAC fuse in the panel near the passenger door for a few minutes. Then reinsert and start the car. Sometimes the HVAC brain loses it's mind on the position of the blend door and doesn't call for the right hot/cold. Removing power and reapplying forces it to move to both extremes and recalibrate.

Another thought is to take care moving the blend door by hand. As seen in the photo posted above there is a plastic clip that is easy to break adding to expense/time repairs.

I too had some minor blockage in the heater core that came on over time. A blast from a water hose and a little brown water later all was good.

Thanks

Mike

 

[LT4John]

A couple of additional thoughts to add...

Try removing the HVAC fuse in the panel near the passenger door for a few minutes. Then reinsert and start the car. Sometimes the HVAC brain loses it's mind on the position of the blend door and doesn't call for the right hot/cold. Removing power and reapplying forces it to move to both extremes and recalibrate.


I removed the fuse and also removed the complete control unit from the dash for a few minutes, still no change.

My condition is when the temp is set a 60, I get cold air for 40 seconds and then it goes hot for 10 seconds, this cycle continues. At 90 I get hot air for a few minutes, then cold air for 20 or so seconds.
I believe my control unit is bad and I am going have to replace it. Need to find a used one.

Thanks for everyones help