vanster

Sometimes my heater works and sometimes just cold air.
I have tried every combo setting possible, even with the AC on.
Not a big deal since I don't live in a super cold climate but it's puzzling.

whatudrivin

Heater control valve under the intake is a likely culprit.

vanster

Does this mean I have to pull the intake manifold off?

dr bob

No. The lower air cleaner housing comes off, and the heater valve is at the back of the right (passenger side on US cars) cylinder head. The failure mode for the valve is leaky/open, making me wonder what might be failing that would cause the system to stay cold. You can pull and plug the vacuum line going to the valve, and you can also observe the position of the little actuator and the plastic arm that connects it to the valve itself. Vacuum retracts the actuator, so you should be able to see that the actuator arm is extended when looking at it engine-off.


Since we have a lot more summer here than winter, I typically add a tie-wrap to the actuator starting sometime in spring. That holds the valve closed even on engine stop and loss of vacuum to the valve. Helps out with engine heat migrating into the heater core on hot days. In the fall, usually early in December, I remember to snip that tie-wrap so I can have heat on cooler mornings. Did you lock your heater valve closed like this? Our December and most of January have been so warm that I've yet to cut the tie-wrap for heat. The last few days have been a little more blustery, highs only in the high 60's, so perhaps it's time to get snipping soon.

dr bob

Oh--- On my later car with auto climate control, the operation of the heater valve is tied through the full-cold position switch on th temp slider, and the blend door valve needs an intact loop through the thermistor in the wheelhouse left front, and the thermistor in the dash temp sensor just to the right of the center console by the glovebox door. Try with the slider in the full-hot position, so the switches override a possibly-failed temp sensor loop.

vanster

Thanks Dr Bob. I have tried all the positions. My guess is that since I recently did a intake rebuild when I had the injectors cleaned that maybe it's loose. As you say, I haven't really noticed it until yesterday when the outside temp dropped to 50 degrees
Most likely I'll fix and never need it again. Certainly don't need windshield wipers anymore.