Outline · [ Standard ] · Linear+ No heat..97 Silverado

[AH55]

Hey guys, got a heater problem with a 97 chevy silverado, 5.7, 4wd with air conditioning. the blower works fine and blows about room temperature air. I do not smell antifreeze or have any moisture on the floor of the truck, nor do I have the windows getting fogged up. Today I changed the thermostat and that did not cure the problem. I felt the heater hoses and they are hot to the touch so I would assume the core is working? I'm not sure if this is relevant, but recently I threw a serpentine belt and ever since putting the new one on, the heat hasnt worked and the AC compressor makes a small grinding noise from somewhere around the pulley. If I put the defroster on, the pulley area of the AC compressor will almost scream. I have read about people taking both heater hoses off and running a garden hose through it to clear debris, is this a good idea? If anybody could point me at something to look at, I would really appreciate it. Thanks in advance for any help.

[TECH II]

If the compressor didn't scream before you replaced the belt, sure you got the correct size?

As for heat, if BOTH hoses are hot, then you have a temp door problem....if one is hot and the other cooler, than the core may be plugged.....clamp the hoses and remove them.....attach a hose to the line of the heater core that was cooler.....flush water through it....use low pressure....you can attach another hose to the inlet of the core, and collect what comes out in a bucket....don't let it just go on the ground where animals can drink it....

Attach the the heater core hoses and burp the lines to get all the air out of them.....

Ran into this on a Cadillac CRT....no heat on one side, heat on the other....had two temp doors, due to a dual system.....confirmed that the temp door was working.....turns out the core was partially plugged, so only one side got heat and the other didn't....BOTH hoses to the core were hot.....TAC said to backflush and it worked....

This post has been edited by TECH II: Oct 23 2009, 12:50 PM

[AH55]

TechII, thanks alot for the response. I think I got the right belt, it's what the vehicle called for and the tension looks right, but I can double check that. It seems to be whatever that plate thing is on the front of the pulley on the compressor making the noise (pardon my ignorance, have no idea what it's called).
I'm about to run out and try the flush you suggest but I'm a little unclear on the method of burping the heater hoses? Thanks again for your help.

[AH55]

Well, I tried flushing the heater core until the water was very clear and put it back together, filled it as the level went down and continued filling and unfortunately, no heat. it seems like it could be a smidge warmer, but could be my imagination.
What is the temp door and where is it located? I'm using a Haynes manual as I have no experience with heaters in vehicles...never had one fail. I cant seem to find it in there. thanks again for the help.

[TECH II]

BEFORE you flushed the core, what was the temp of both hoses?

What is the temp of both hoses now? Both hot, or one much hotter than the other?

[smj999smj]

The part on the front of the AC compressor is the AC clutch. If the clutch is engaged (it'll be turning with the pulley) and there is a "screaming noise," you could have a bad compressor...or a clog in the system. Use AC gauges to confirm pressures. If the clutch is disengaged and there is noise, you could have a bad AC clutch bearing. As far as the heat, it sounds like a mode door issue in the heater case. The temperature door electric actuator is located on the passenger side, inside the vehicle, attached to the front of the heater case. Observe it's operation while cycling the temperature select between hot and cold

[AH55]

Tech II- before I flushed the heater core both hoses were equally hot. Afterwards they are still both equally hot. I actually tried to find the cooler of the two, but ya really can't tell.

smj999- The AC clutch makes the screaming noise when I engage the defrost and when I don"t it sounds grumbly, like a bad bearing as you stated. When you say the temp door is in the vehicle on the passenger side, would that be in plain view or having to tear the dash apart or something? I see some black boxes that look like they are associated with the heating system right above the passengers foot area.

[TECH II]

I said if both hoses were hot, you had a temp door problem, not a core problem.....

Remove the glove box to get access to the temp door actuator motor....two screws hold it in place.....manually move the linkage to the door to see if you now get heat, to confirm the door/linkage is not broken......if ok, command the temp cold to hot, to see if the motor moves.....

[AH55]

TechII- Yeah, I know you were saying temp door all along if both hoses were hot. I figured it was cheap and easy enough to flush the core, so I might as well just to eliminate it. It sounded like the cadillac you were mentioning had both hoses hot and still responded to being flushed, but perhaps thats a different situation due to being a dual system. Oh well, I'll tackle the temp door this afternoon and let ya know what I find. Thanks a ton for the help.