Zero Heat

[special-K]

I finally got my '95 Suburban's heater control replaced but the fan barely worked then stopped. I have a new blower motor and fan resistor still to install. But I am getting no temp what so ever drifting out of any vents. The temp gauge shows proper warm up temp, but I will check the thermostat for sticking open. I really think it's something else. By the engine temp I should at least feel slight warmth at the vents. Nothing.

I'm not familiar with how the heat system in these trucks works. Is there any sort of control that could affect this? What does the temperature door motor do? Could it allow no temp passage at all if not operating? Could a bad air inlet door block temp 100%?

I know it would help to have the blower working. I'd just like to get my ducks in a row for this other problem before getting into it so I can get it all at once.

[sntrym95]

There are three actuators that control where the air is going. First is the vent type (defrost, floor, or front vents), a blend door that controls the temp, and a recirc door which allows or prevents outside air from being used. All of the air passes over the heater core and AC fins (unless you have the heater core bypass solenoid for use with AC).

If you aren't getting anything, the recirc door is probably closed. The actuator may be toast. It's the most fun one to replace too. The control unit in the dash could be the culprit as well. You'll need to test voltage at the actuator connection to validate it's not the control unit.

[sntrym95]

If you remove the blower motor, you should be able to get to the flap that allows air in and out. Try moving it, they get stuck sometimes. IIRC you have to reach up a bit into the motor housing to get to it.

Another thought - since you have a burb, you probably have the bypass solenoid. It should be the passenger side heater hose under the hood. Those are known for failing. I'd check that first. Remove it if you want and run the heater hose like the trucks. The SUVs had them because of the amount of space that needed to be cooled and keeping engine heat from the heater core provided colder air.

[Just call me Sean]

When you change the blower, have a vacuum handy to clean out all the leaves and crap that blocks the airway.

[special-K]

Thanks for the info so far. Today I put my hand up to a dash vent and, while it is cold, I feel air pushing out. I'd think if the blend door is stuck shut causing cold air I wouldn't feel any air movement or the air movement would have some degree of warmth. I was wondering if the culprit could be the control panel I put in. It's from the junkyard. Could be no good or maybe when I adapted to the '96-up controls I did something wrong.

[ChevyTech]

Those control heads were known to fail.
The transistors are a weak point.

If it ends up the control head is the problem, here is a thread from another chevy truck board that might help. There is part information too.
https://www.chevytalk.org/fusionbb/s...ecbce0c900bf9/

Here is a photo of the control board. It only has two of the transistors circled so notice there are others. Somewhere I had information on what each transistor does but I can't seem to find it. I will look some more tomorrow.

[Accelo]

Air or no air? I am wondering if both heater hoses are warm?

[special-K]

Originally Posted by ChevyTech

Those control heads were known to fail.
The transistors are a weak point.

If it ends up the control head is the problem, here is a thread from another chevy truck board that might help. There is part information too.
https://www.chevytalk.org/fusionbb/s...ecbce0c900bf9/

Here is a photo of the control board. It only has two of the transistors circled so notice there are others. Somewhere I had information on what each transistor does but I can't seem to find it. I will look some more tomorrow.

This helps a lot. The '95-only panel had me stumped. I finally adapted the wiring to install a JY '96-up panel but fan was dead (I assumed) so never got anything working. But even in the summer I felt no warmth out the vents. I assume the fan switch is it's own animal and the blend controls are integral to the control panel. So could have fan and not have one or the other or both functions. I'll do the fan and resistor over the holiday... I hope.

I just went to Ebay to see if the panels include the fan switch and the first listing offers "Save up to 12% when buying more" . Are they admitting you'll wish you bought more than one when the first one goes dead in short time?

Originally Posted by Accelo

Air or no air? I am wondering if both heater hoses are warm?

Yes, both feel warm and same temp.

[MiniD]

If you have heat on both sides of the heater core then you have flow through the core. Are you sure you're checking the lines into and out of the core? I'm not sure when Chevy started with the bypass line for the heater core.

[special-K]

I'm feeling both hoses direct from the firewall.

[MiniD]

That implies the heater core is seeing hot water. Your problem, then, is either no airflow across the core or whatever controls mixing <blending> hot/cold air isn't moving.

[special-K]

Thanks for that advise. I'm thinking the same. I'm just not familiar with the system. I wish I had the Helm book or a parts truck to tear into and explore. I didn't get the fan installed today like I had hoped. That will make it more obvious if the vent blend is working. If that is also not working I'm buying a new control head first and see what that does. Could be the one I got at the junk yard is actually junk! I just liked the idea of a GM unit, even if used, over going with the replacement part. Also, it would be quite a coincidence if while my heat system was out of use these parts failed when all it needed was a new fan switch and while replacing the control head busted it's mount clips... which led to adapting '96 up unit.

[Just call me Sean]

I know I don't get any heat out of the 93 or 99 when set to cold, not even a little bit. I still need to change the temperature control motor for the 99. It was sticking on heat so I unplugged it on cold until I get around to it. It kind of sucked the one cold day we had and I turned on the defroster, the a/c compressor kicks on when set to defrost.

[MiniD]

As someone else eluded to... if you're changing the blower motor/fan, be sure to vacuum out the space between the blower and the heater core. It is just up and to the left of the blower motor opening.

[sntrym95]

Also, if you have the motor out and are cleaning the heater core, wash it out too. These trucks don't have cabin filters and the fins get filthy. Great tutorial here: http://www.chevytalk.org/fusionbb/sh...php?tid/282054

[special-K]

Great tips I'll be sure to do. Thanks for the tutorial.

A thing about this Suburban is it has no bypass valve in the heater line that from what I understand Suburbans normally have (from what I've read). I suspected that could be the cause. Not sure what's up with that. This is a municiple/gov't vehicle package base (Cheyenne) model, former Cobb County Georgia Sherriff's Dept K-9 unit. I don't have others to compare to but I believe some features are an exception and this may be another.

[Just call me Sean]

Yea, you might want some a/c fin cleaner handy. This was my evaporator in the 93:

[special-K]

How inefficient . Mine will need it I'm sure. Fixing exhaust today and hopefully get time to get into this part of the repair