Difference between blend door, actuator, and HVAC programmer

[BryanB]

Before I start tearing things apart, is there any way to tell what the problem might be before I dig in? On my 91, I get no heat coming out of the vents, floor or dash. The heater hose lines to the heater core both heat up and the blower fan for the inside works fine.

Just looking for any clues that point me more towards one problem vs the others.

Thanks

 

[Scottsredvette]

When my 89 did that, it was the vacuum actuator. It failed and none of the vent doors for the floor or dash would open. Couldn't find anyone that would fix/rebuild it so my favorite Corvette mechanic found a NOS part. PITA to get to but that fixed it.
Where in Colorado are you? Rik at the Corvette Center Of Colorado Springs south of CS is who found the part for me.

 

[ecss]

Before I start tearing things apart, is there any way to tell what the problem might be before I dig in? On my 91, I get no heat coming out of the vents, floor or dash. The heater hose lines to the heater core both heat up and the blower fan for the inside works fine.

Just looking for any clues that point me more towards one problem vs the others.

Thanks

If air blows out of the vents properly and just no heat.

Look at the top of the evaporator housing under the hood passenger side of the firewall.
There are two electrical connectors that plug into the blower control module which is inside
the evaporator box.

Unbolt the module and pull it out. You can leave the two electrical connectors unplugged the blower motor
will be disabled.

Look inside the opening and you will see the blend door. This is what deflects the air across the heater core
or around it.

Turn the ignition on. No need to start the engine.
Manually adjust the temp rocker up switch to display 90 degrees. You should hear and see the actuator motor moving the blend door.
Manually adjust the display to 60 degrees. You should hear and see the blend door moving to the other extreme position.

If that works the blend door, actuator motor or Programmer are not the problem.

 

[BryanB]

Thanks for the replies. I'll go out later and check those out.

Scott, I am east of Colorado Springs but I know where Corvette place is. Drove past it several times.

 

[BryanB]

Ok,got the module out , turned the ignition on and adjusted the buttons all the way up and down. I did not see or hear the blend door move at all.

The blend door was open about 1/2" but I never felt any heat since I've had the car.

Here is a word of wisdom to share:
When removing the blower motor module, there are 4 screws holding the module/plate on top of the evap box. Only remove the 2 7mm screws. The 2 1/4" screws hold the module to the mounting plate. When you remove the screws and electrical connectors the module will drop inside. I had to get my 6yr old daughter to reach her hand inside to retrieve it :L

 

[ecss]

Ok,got the module out , turned the ignition on and adjusted the buttons all the way up and down. I did not see or hear the blend door move at all.

The blend door was open about 1/2" but I never felt any heat since I've had the car.

Here is a word of wisdom to share:
When removing the blower motor module, there are 4 screws holding the module/plate on top of the evap box. Only remove the 2 7mm screws. The 2 1/4" screws hold the module to the mounting plate. When you remove the screws and electrical connectors the module will drop inside. I had to get my 6yr old daughter to reach her hand inside to retrieve it :L

When the blend door motor is told to move, the Programmer monitors the feed back signal for the motor.
If the feed back signal is not correct a green led on the HVAC control head panel should flash.

When you hold the up or down temp. switch to 90 or 60 does your auto light come on?

You can also try this. Disconnect the negative battery terminal for a couple of seconds then reconnect it.
turn the ignition On.

The HVAC will go through a recalibration of the blend door. Takes about 30 seconds. The blend door
is moved to the two extremes then to the position where the temperature is set. When done the
Blower motor turns on. Pressing the Off turns the blower off.

I don't think you need to reconnect the blower module connectors for this test. You just want to see
if the blend door moves during the 30 seconds it recalibrates the blend door position.

 

[BryanB]

Well, the blend door does open.

Turned the key on and the heater control was already on auto. Switched to off then began adjusting the up/down arrows to 60 & 90. It immediately switches back to auto

 

[ecss]

Well, the blend door does open.

Turned the key on and the heater control was already on auto. Switched to off then began adjusting the up/down arrows to 60 & 90. It immediately switches back to auto

Are you saying the blend door is moving?

Look at this Youtube video.

It shows how to verify if there are any system faults. 01 or 02 would be blend door faults.

https://www.youtube.com/watch?v=lWIrT8tN-a8

 

[BryanB]

Yes, the blend door inside where the blower motor module fell in opens and closes.


Watched the video and went out to test. I put the blower motor module back in. I have air blowing out of the proper vent when I press either the dash vent or floor vent. Let the car warm up to until the cooling fans kicked on, still no heat. I checked all the hoses and they are all hot.

I posted on a different site about this other issue that must be related.

I can leave it run in the driveway and the engine heats up to operating temps and the fans will turn on.
I drove it for 15-20 miles and the temp gauge never went above 150-160 (best guess looking at the gauge). I put in a 160 t-stat a while back. Anyway, after the 20 mile drive it was making the gurgling sound when I shut it off.

Radiator is full and I made sure to get all the air out of the system.

It sounds like the coolant is boiling inside the the tank where you fill the radiator.......aaaahhahhahahha

 

[BryanB]

I'm almost wanting to say the heater core is blocked. I hope not ad

 

[ecss]

I'm almost wanting to say the heater core is blocked. I hope not ad

To verify if the heater core is block all you need to do is remove the hoses at the heater core. Attach a garden hose and verify the water goes in one pipe and out the other. Just have to make sure when you disconnect the hoses you don't move or bend the heater core pipes. You could break the joint where the pipe meets the heater core. :ugh

160 is to low of a temp.

Do you have a infrared no contact temperature gun to point at the heater core?

Something is strange because the fans shouldn't come on until around 223F unless the Eprom has been
reprogrammed. If the car is overheating, you should see antifreeze spewing into the plastic overflow tank.

 

[BryanB]

I went with the t-stat O'reilly Auto listed online. I picked it up in store and verified the same number. Look exactly like the one I took out.

I'll check the heater core like you mentioned in a little while. Have to eat and let the car cool a bit more

Thanks again

 

[ecss]

I went with the t-stat O'reilly Auto listed online. I picked it up in store and verified the same number. Look exactly like the one I took out.

I'll check the heater core like you mentioned in a little while. Have to eat and let the car cool a bit more

Thanks again

I forgot you have a L98. I was thinking you had a LT1 which used a special thermostat. ad
But I would put a 195F back in.

 

[ecss]

I went with the t-stat O'reilly Auto listed online. I picked it up in store and verified the same number. Look exactly like the one I took out.

I'll check the heater core like you mentioned in a little while. Have to eat and let the car cool a bit more

Thanks again

If you have enough slack in the heater hoses, take a razor blade and slit the hoses at the pipe. That way
you won't damage the pipe when you remove the hoses.

I forgot you have a L98. I was thinking you had a LT1 which used a special thermostat. ad
But I would put a 195F back in.

 

[BryanB]

I probably will put it back in. I changed it out when I was trouble shooting some earlier issues.

 

[BryanB]

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This is getting better by the day....

So I went out to remove the hoses from what I was thinking was the heater core. Drained it, used hose to spray inside and saw water coming out of the other hole. Cool, heater core not plugged...then it hit me..this is the surge tank, not the heater core. "Where are the hoses for the heater core?" i thought. I started looking around and finally under the surge tank only to see 2 metal pipes coming out of the firewall.

The question now is did the previous owner disconnect it because the core was leaking? I have no issue spending $40 on a new core but its the 6 hours of ass pain it takes to swap it out.
Easier they say for smaller people but I'm 6'@240 with small baseball glove size...hahaha

 

[ecss]

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This is getting better by the day....

So I went out to remove the hoses from what I was thinking was the heater core. Drained it, used hose to spray inside and saw water coming out of the other hole. Cool, heater core not plugged...then it hit me..this is the surge tank, not the heater core. "Where are the hoses for the heater core?" i thought. I started looking around and finally under the surge tank only to see 2 metal pipes coming out of the firewall.

The question now is did the previous owner disconnect it because the core was leaking? I have no issue spending $40 on a new core but its the 6 hours of ass pain it takes to swap it out.
Easier they say for smaller people but I'm 6'@240 with small baseball glove size...hahaha

Look at this diagram closely. It's hard to see but item 1 and 7 are the hoses for the heater core.
One hose goes into the core and the outlet hose from the heater core goes to the surge tank.

Yes the two metal pipes coming out of the firewall are the heater core. Those are the two pipes I was talking about will break loose from the core if you pull on the hoses and is why I said to slit them if there was enough slack in them. :L

The blower motor always blows air through the AC evaporator.
The blend door depending on the temp. will determine how much air is blown on the heater core and how much air is bypassed around the heater core. You can see that when you look through the hole when you removed the blower control module.

Diagram of the heater hoses for a 95 but the 91 should have basically the same layout.

 

[BryanB]

Thanks for the pic. Tomorrow I will try the garden hose trick on the heater core to see if it is in fact leaking...after I put plastic and towels in the floor board. If needed, my weekend is free. I will make plans to swap the heater core :ugh

I can't imagine they would have disconnected it for any other reason

 

[ecss]

Thanks for the pic. Tomorrow I will try the garden hose trick on the heater core to see if it is in fact leaking...after I put plastic and towels in the floor board. If needed, my weekend is free. I will make plans to swap the heater core :ugh

I can't imagine they would have disconnected it for any other reason

You're saying the heater core inlet hose has been removed and now goes into the surge tank?

Sounds like Bubba was the former owner. :ugh

 

[Otter]

Thanks for the pic. Tomorrow I will try the garden hose trick on the heater core to see if it is in fact leaking...after I put plastic and towels in the floor board. If needed, my weekend is free. I will make plans to swap the heater core :ugh

I can't imagine they would have disconnected it for any other reason

Good luck, grimacing thinking of the job ahead of you. Replaced one in an 89 I had and it wasn't fun. Friend said the car is built around the heater core and thus it is part #000001.