The heater on my 1989 vette only blows hot air no matter what buttons you push on the digital control. It does shut off when engine is turned off. I have read that there is a fuse located under the hood near the blower motor. I have not been able to find one. I am suspecting the heater control module, but hate to replace it and find out it was a fuse. Where is the location of the heater control module?
Where is the fuse ( if there is one )?

well, first off, welcome!

It only blows hot air? Does that mean it blows only hot air out of all ducts? It sounds like a software problem in the controller.

Lemme throw some thoughts out:

So it only blows hot air.

Does it move air even when supposedly off?

Does it change air location, meaning, if you hit defrost, does the hot air go up to the windshield?

What speed is the fan running at?

Can you change fan speed?

Does the cruise control work ok?

How does the engine run? (sounds silly, eh, watch the next statement)

There are a number of vacuum lines that pick up on the right side of the intake manifold. One has a check valve on it; that one feeds vacuum to the climate controls. If that is damaged, funny things start happening.

On the heater lines, there is a vacuum dashpot. This is under the hood and controls hot water flow. Is their a vacuum line?

There is a site called www.doctordons.com, IIRC, they service the electronic climate control head units (C68). Their service is about $100. Seems worth it, depending on what else we learn here!

Quote:
Is in a weather-pak housing usually bolted to one of the bolts that hold blower motor into A/c ducting

Quote:
The fuse and blower control module only affect fan speed ; have nothing to do with temperature

Welcome to the site!

Sounds like this is the blend door not opening to adjust the heat/cold. It's not uncommon, there is a metal rod attached to a motor via a plastic clip. Sometimes the clip breaks or slips out. You can get a new one in the "help" section at the auto parts store. I have personally never experienced this, but AFAIK the motor/clip are accessed through the passenger side foot well. Remove the hush panel and the ECM and you can look up and see it. I believe you can also see if the door is functioning by removing the top relay from the blower box inside the engine compartment on the passenger side.

Here is a diagnosis schematic courtesy of a member on another site:

http://members.shaw.ca/dankai/HVAC%20Electrical.pdf

Good luck,

Matthew

oh, yea, forgot about that damned blend door. They get rusty, too. The servo can't work it...

You may need to lube things.

This article led me to my solution
http://www.batee.com/corvette/acrepair/c68pgmrboard/index.htm

i had the oppisite problem on my 89. ended up being a heater-a/c control module.

I think I found it but if the blower works ok no need to check it, is there? The blower speed control seems to work ok. There appear to be 10 speeds and the speed increases from 1 to 10 everytime you push the speed up button and back down from 10 to 1. When you push the off button it seems to turn off but it still puts out warm air.

So the problem is with the mixing door.

The problem? Reaching said mixing door.

Here is what I can tell you so far.

So it only blows hot air. Yes,only hot air no a/c

Does it move air even when supposedly off? Yes, but it is
a lower speed. But when you are driving it is enought to make you roll down the windows.

Does it change air location, meaning, if you hit defrost, does the hot air go up to the windshield? The only change you can make is to push the defrost. It seems to put warm air out no matter if the defrost is pushed or not.

What speed is the fan running at? When it is turned off I believe it is still blowing, probably at low speed.

Can you change fan speed? Yes... there are 10 speeds and in the manual position it will increase from 1 to 10 and back from 10 to 1

Does the cruise control work ok? Yes

How does the engine run? (sounds silly, eh, watch the next statement) When I was driving it after it was warmed up it seemed to idle rough when you stopped at a stoplight. Today I just pulled it out of the garage and let it idle while I did all the checks and it seemed to idle just fine.

There are a number of vacuum lines that pick up on the right side of the intake manifold. One has a check valve on it; that one feeds vacuum to the climate controls. If that is damaged, funny things start happening. I didn't find any
rubber vaccuum lines. Is this what I should be looking for?

Would being low on refrigerant cause this? By the way does 1989 use R134?

Any chance of seeing it if you remove the radio?

I suppose you have to remove the carpet first to get at the panel to be removed to get access to it.

Thanks.... it may take me a while to wade thru all of this.

You still need to inspect the blend door to see if that is the culprit. First place I'd look.

As far as the a/c system, stock was R12. So it should be that unless someone converted it. If it was converted, it should have a conversion sticker usually near the blower motor/firewall and adapters on the a/c lines in the engine compartment.

Matthew

Is this blend door above the heater control on the console?
Can I see it if I remove the radio? or is it on the exterior
side kick panel? I'm a little confused as to where to start.

Quote:

No to all. Look at my post above. You can physically see the blend door operating if you remove the relay from the top of the blower box inside the engine compartment on the passenger side. It should have about three wires at the plug and the plug is mounted straight down. Two or three screws and you can remove the relay. Have a friend move the temp from hot to cold and see if the door moves. If not, you likely have a disconnected linkage from the motor. This is accessed by removing the passenger side hush panel and ecm (shiny metal box held in a white plastic case and fastened by two screws) and looking under the dash. You will see it attached under the black plastic air box.

Matthew

I tried to post a couple of pictures to better describe what I am seeing but they were to large. I found the blower motor which is mounted in a round black box which I would consider to be the blower box. There is no relay there. Next to it on the right mounted to the firewall is what appears to be a fuse. It has 2 purple wires coming out of it. Next to it on the right toward center of car are the 2 heater hoses that go thru the firewall. Next to it on the right almost next to the valve covers there is another box about 10" long and it splits in the middle lengthwise held to gether with 2 screws. It has what I believe to be an air conditioning line going into the forward end of it.Between it and the valve cover is a removeble ???? with 2 connectors which I believe (from seeing other pictures of it)is the heater blower control module. This is held in with 3 screws and the wires going into it are pointing down. Is this what you are referrng to as a relay? This, as far as I can see is the only thing that can be removed, has wires on it pointing down.

See pic below of evaporator case.

Attach file:

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  evaporator case.JPG (0.00 KB)

Thanks.... This helps tremendously. I didn't realize that everything pictured is all part of the blower box. I had pretty much narrowed it down to this as the only thing you could unbolt with 3 screws and remove. Is this the heater control module that I am removing? Thanks again for taking the time to post a picture. I really appreciate it.

That's actually the fan blower resistor. It's what allows the fan to blow at multiple speeds.

Thanks I have it pulled out and took some pictures which I will try to attach. The only thing I see looks like a stainless steel cable.... Should I be able to see the door itself? Also, since the blower is electronic I am assuming
I will need to hook the battery back up before having some one push the red and blue buttons while I look for movement in this cable? Right? The file is 1374KB so it is also to large.

shrink the pic down to under 1 meg, so it will upload.

For jobs like this, I don't disconnect the battery, not worth the angst for any future trouble shooting.

The door is kinda dark, but, you should be able to see it move, or, the cable do something when activated. Also, there is no need to start the engine, just use the battery to cycle the climate contols.

The motor that drives the blend door is hidden under the "hush" panel above the passenger floorboard. I found it simpler to remove my seats to get under both side of the dash. You did check the programmer? The resistor solder joints failed on mine. Real pain to get to and remove. All of the vacuum lines are controlled by it. It is above the hush panel on the drivers side. On mine when the unit first comes on it actuates the blend door as if it is relearning its position. When my blend door was not actuating it turned out to not be the blend motor but the solder joint on the resistor in the programmer.

Update... I have the relay under the hood pulled out. The only thing I see looks like a ss cable on the bottom at the back near the fire wall. I have the hush panel removed and on the right side high up there is a little door. It moves
seems to be spring loaded. You push on it and it returns to closed position. I have the radio, and heater control pulled out. Thought this is where I would find the cable that controls the door. What does the cable attach to and where is it located? The electronic control seems to work in the heat mode and the fan speed goes up and thru all 1o positions. I can't hear the compressor kick on when I push the air cond. button on heter control. Could it just be loe on freon? Would this cause the symptoms I am seeing? If it is the air I have some questions about the replacement freon
One person told me that there is a new R12 blend on the market that can be mixed with R12. Another person told me that it is ok to mix R12 and R134. What are your thoughts on this?

You need to see if the door moves when you change the heat/cold setting. Don't try to force the door with your hand. I don't know if you can see it without the ECM removed, so make sure you're looking at the right door. The door is controlled by a motor with a plastic rod, so I'm not sure if you're looking at the right thing.

As far as the refrigerant, never mix r12 with anything. Here is a site with a little info on alternative refrigerants:

http://www.aa1car.com/library/tr497.htm

Matthew

Foung this article about Freon

http://www.aa1car.com/library/tr497.htm