Heater temp and air flow problem

[stevemoble]

First post, let me try to be a specific as possible.

I have a 2001 FWD blazer 80K miles. Basically I don't have any heat coming out of the vents, just cold air regardless of the setting on the temperature control (manual).

In addition to this problem, the air vent directional control does not function. Regardless of the position, it blows the air through the dash vents. The A/C works, but this past summer I had a short period of time when the compressor just stopped for no reason and after about 5 minutes it restarted. That seems to have resolved itsself (false hope, I know).

The BCM was replaced about two years ago. The cooling system has been serviced and the hose temperature in and out is the same.

I have disassembled the dash and see the various vacuum pots and hoses. I removed the switch panel for the heat and all the wires seem to be snug. Shaking various wires does not change the result. I have checked the fuses at the end of the dash and they all look ok although I haven't replaced them. The one fuse under the hood for HVAC in the box also appears OK. I can also report that the body control module shares circuits with other componets such as the crusie and the instrument panel. Everything else seem to be working OK. Given that two of the three controls on the switch panel are not working I would suspect electrical but just a guess on my part.

Any help would be appreciated. Chevy will charge me $49.00 just to tell me whats wrong.

[RaeRae1]

Originally Posted by stevemoble

First post, let me try to be a specific as possible.

I have a 2001 FWD blazer 80K miles. Basically I don't have any heat coming out of the vents, just cold air regardless of the setting on the temperature control (manual).

In addition to this problem, the air vent directional control does not function. Regardless of the position, it blows the air through the dash vents. The A/C works, but this past summer I had a short period of time when the compressor just stopped for no reason and after about 5 minutes it restarted. That seems to have resolved itsself (false hope, I know).

The BCM was replaced about two years ago. The cooling system has been serviced and the hose temperature in and out is the same.

I have disassembled the dash and see the various vacuum pots and hoses. I removed the switch panel for the heat and all the wires seem to be snug. Shaking various wires does not change the result. I have checked the fuses at the end of the dash and they all look ok although I haven't replaced them. The one fuse under the hood for HVAC in the box also appears OK. I can also report that the body control module shares circuits with other componets such as the crusie and the instrument panel. Everything else seem to be working OK. Given that two of the three controls on the switch panel are not working I would suspect electrical but just a guess on my part.

Any help would be appreciated. Chevy will charge me $49.00 just to tell me whats wrong.

It sounds to me like two separate issues. The cold air may just be low coolant level. If both hoses are the same temp and both are getting warm, you may want to start the vehicle with the radiator cap off, let it get warm enough to open the thermostat, rev the engine a few times and check the level in the radiator. It may just be low. Fill to full and see if that helps.

The other issue could be electrical or vacuum depending on how your system switches the vents. Often times it is done by a vacuum not an electrical "switch". I am not sure on this one, maybe someone else has more info on the vacuum for the vents on your particular vehicle.

[stevemoble]

Thank you for the reply, the coolant level is OK, I've bled the system, both hoses warm to hot but equal.

I've accessed the switch cluster and there are vacuum lines and electrical connections on the air flow control switch and an electrical connection on the temperature control. I believe the temperature is controled by a mix of warm air and cold air flow.

[MT-2500]

Originally Posted by stevemoble

Thank you for the reply, the coolant level is OK, I've bled the system, both hoses warm to hot but equal.

I've accessed the switch cluster and there are vacuum lines and electrical connections on the air flow control switch and an electrical connection on the temperature control. I believe the temperature is controled by a mix of warm air and cold air flow.

Welcome to AF on your first post.
Is it automatic or manual ac/heater controls?
Make sure you are getting good vacuum from engine.
Vacuum runs from engine intake to a vacuum tank and then back to heater controls.
Lot of plastic lines that break or come unplugged.
A good eyeball inspection will help find a broken or unplugged one.
If you do not see any problems.
Get a good vacuum gauge and test it all of the way from engine to the heater controls.
MT

[stevemoble]

It is manual, I haven't located the vacuum tank yet but none of the vacuum lines appear to be damaged and the engine runs fine. I'll go see what I can find, thanks.

[MT-2500]

For the vacuum tank look in the right front fender apron area.
It is almost hidden.
Check for good vacuum in and out with a vacuum gauge.
Good luck MT

[peterjon1]

Does the 4wd work? Your vacuum lines aren't filled with transmission fluid, are they?

[stevemoble]

No fluid in the line but as sugested earlier, two problems...I've sort of fixed them. On one of the "Pots" for the vacuum system that controls one of the doors, the line was loose and the plastic shroud cracked. Fixed it with tape and re attached, all doors and air movement fixed.

I went ahead and redid the heater core flush because of a gurgiling sound. I read somewhere that was heater core realted. Anyway, I have about 1/2 the heat I expected so I'll need to reflush the heater core.

I appear to be on the road to recoevery, thanks to all who replyed.

[stevemoble]

On a totaly unrelated matter, or maybe not, on the housing for the thermostat, there is a "plug". Looks like a 1/2 inch square drive and about a 3/4 thread. Just screwed into the housing. Can anyone tell me what that is and what it's used for.