1998 QX4 heat control valve?

[Marc22692]

Hi everyone my name is Marc. I have a 1998 QX4 that has 192k on it and runs like a champ. My wife drives it most if the time and when she went to work the other day she noticed that when she turned on defroster, as it was the first semi cold morning this year, that the heat would not engage. Meaning, it was blowing full blast set to 85 Degrees but even after 20 miles it seemed to be blowing really cold air. So I thought maybe it was thermostat because upper coolant hose was hot but lower wasn't at all. Also the heater coil hoses were cold after warm up with heater engaged. So I replaced thermostat. That was a waste of time as after I was all done I tested it in hot water and the thermostat worked fine. So the million dollar question is.... Is there a heater control valve, if so where is it located, do it use vacuum or electric if there is even one, can I hold it open manually, and finally am I even on the right track? Thanks ahead of time fir any responses!

Marc

[Towncivilian]

Welcome to NICO!

There is no heater control valve. Your heater core could be clogged. What is the service history of the engine coolant on your QX4?

[Marc22692]

Thanks for the response towncivilian! All service upto date. I did go through self diagnostics on the auto amp. It pass all test bit I noticed that the 41-46 test wasn't allowing the air mix door motor to engage. I ripped off the glove box and the center dash and found this stupid little servo motor wasn't opening the door to the heater core. After some fine finessing and some old r/c repair knowledge I rebuilt the air mix door motor and she works great! It was a long day but "grandma" as we call her is back on the road and heating the family nicely!

Marc

[Towncivilian]

Glad to hear you've fixed it and had the experience to fix it easily! I've never heard of any of the various door motors die or malfunction, so this is a first. They're usually pretty reliable.

[Marc22692]

there isn't much to them, so I hear you!Thats why I never even thought it was a possibility, so i overlooked it. But at this point i would love to see her get to 300K and still have everything working!!!