Hot air entering cab

[east302]

The hose from the solenoid to the water valve should be on the lower port.

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From the top port, it was a hard line across the intake to the PCV valve fitting:

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GM part number 15971641 but likely discontinued. Junkyard would be a good source (they weren’t used on pickups) or just a length of hose.

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Parts diagrams are here but you can’t buy anything from them:

Spare parts catalog Chevrolet EPC Online > nemigaparts.com

Parts catalogs. Spare parts catalog Chevrolet EPC Online.

nemigaparts.com

 

[BigWaveDaveAZ]

I'm having the same problem with my 98 Tahoe. For some reason, I don't have the hard line that comes from the top vacuum fitting, don't know if it ever had it. Mine, for some reason just started blowing hot air through the vents and I have no control over the temperature of the air that comes out. If it doesn't have it, what do you use to by pass it?? Thanks for your help.

 

[east302]

It would have had the line (your PCV fitting would have the port as well). The valve is normally open - you can push up on the rod at the side to verify valve closure. It should return to the down position, leaving the valve open.

The valve only closes when the MAX detent on the temperature dial is selected to shut off flow and maximize a/c performance. Since you don’t have the vacuum line, the valve shouldn’t function and should remain open. It doesn’t modulate or have any other control over air temperature if that’s what you were wondering.

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The usual culprit is that your air damper actuator at the heater core is not adjusting to blend warm/cool air. It’s the one roughly behind the ashtray and power ports. There is a notched silver dial on the actuator that rotates as the damper moves. Raised lines on the actuator show the range of movement. See if it’s turning smoothly from one end to the other as you adjust the temperature dial.

It has plastic gears inside that tend to crack.

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[BigWaveDaveAZ]

I double checked, and my vacuum solenoid on the firewall only has one vacuum line coming from there to the heater hoses, the top port is open. I dont have the hard line from the top port to the PCV fitting. It worked for 2 1/2 yrs and the out of the blue started blowing hot with no temp adjustment. With that said, can I pretty much go right to the air damper actuator, or do I also need to look at the piece that goes in between the heater hoses that opens and closes the valve for the Max detent? Thank you for your reply.

 

[BigWaveDaveAZ]

Are their more than one of these air damper actuators, and are they the same?? If so, is this one shown the one that is behind the power outlets??

 

[east302]

With that said, can I pretty much go right to the air damper actuator, or do I also need to look at the piece that goes in between the heater hoses that opens and closes the valve for the Max detent? Thank you for your reply.

Correct. If you had no heat, then the valve could be the culprit but not if you do have heat.

There are three actuators: one above the blower at the recirculation damper, one at the heater core (blend actuator) and one by the gas pedal which directs air to floor-panel-defrost (mode actuator). Believe that the blend and mode are the same part number but check on Rockauto to confirm. Yes, the blend (hot-cold) actuator is the one behind the power outlets.

To me, your symptoms sound like an actuator issue. Internal plastic gear probably cracked.

 

[BigWaveDaveAZ]

I thank you sir, I appreciate all your help. I will start with the one behind the power outlets.

 

[BigWaveDaveAZ]

I purchased the new actuator, I am replacing the one behind the ash tray/power ports. We replaced it. Any secrets on how to get the screw on the right back in. We took the new actuator out thinking we could try something different to get the screw in, now we can't get the actuator to fit back in place. For some reason we can't get the big actuator hole back on the shaft that opens and closes the door. Is there a way we threw the timing off or have to reclock something to get it to slide back on. We just can't get it back on the shaft and have everything line up again.

 

[east302]

The only time that I’ve replaced that one I had the dash out. The actuator should be keyed to the shaft so I’m pretty sure that I just rotated the damper shaft to line up with the actuator.

Sorry, probably easier said than done with the dash in place. @someotherguy may have some suggestions.

 

[BigWaveDaveAZ]

Ok, I thank you sir. I have the bottom of the dash off, the ash tray and power outlets removed and still can't get it. We are back at it again today. I thank you again for all your help, it's much appreciated.