Intermittant heat

[sempar]

My 2001 has started to go intermittent on the heat just when it's getting col here. Both sides are affected, so it's not one of the actuators. Running through the selector settings or changing the temp setting makes no difference. Most times it works correctly but it seems to be getting worse. Considering how quickly it will switch back and forth ( heat / no heat ) I'm thinking it's a poor connection on the cabin temp sensor in the aspirator tube. According to the Service manual it requires you to take off the knee bolster ( no problem there ) but it also requires you to remove the Trim Plate Bezel - IP Cluster, which seems ridiculous, and a big pain in the arse.

Is it really required to so this to check the temp sensor or wiring?

John

[phewop118]

Just to confirm, you're talking about air temperature, not blower speed, right?

Are you positive your coolant is circulating well? An air pocket can cause very similar symptoms, especially when idling. Does heat come back when you raise rpms?

Another thing to check to try and rule out the temp sensor... does the problem go away when you have the temperature setting to max heat (90)? If I'm not mistaken, at that point, it will just command the temp doors to be at full heat, regardless of temp sensor feedback. If it stays hot, then you probably do have either a temperature sensor or door actuator failing. A scan tool should help diagnose from there (even a Bluetooth scanner that can read body codes, as the dash module will set codes for any sensors or actuators out of whack).

[Paulaurora]

probably door actuator failing. but I had issue with early head gasket issues where heat was working intermitted .

[kbpickle]

Not sure if this helps, but please note there is also a cabin temp sensor over the front passenger footwell accessible by only the removal of the "Closeout/Insulator Panel - Right" via removal of two Phillips head screws and one push-in retainer. Then remove the sensor from the panel with a quarter turn anti-clockwise. Not sure how you would test the sensor itself at that point.

kbp

[sempar]

Engine coolant temperature is stable, with no drop in coolant level. Blower speed is fine, just air temperature at the outlets will occasionally go cold regardless of temperature display setting. I also noticed that I'm not getting any suction from the aspirator inlet on the dash, so it's something I'll look into. As kbpickle noted , I'm leaning toward the cabin air sensor or snesor connection, since the thermistor operates from a 5V reference. and a bit of corrosion or loosness will cause a change in reading, resulting in temperature fluctuations. Easiest way to check the thermistor ( sensor ) would be with a VOM, but I'd have to find the resistance values to temp table. Could also switch out one of the other four sensors to see if it works correctly. So...... looks like I may have to take the dash apart as kbpickle noted. I'll do it after I've eliminated other scenarios, though I'm not looking forward to it.


John

[sempar]

I thought I'd bring this topic to a close. As I mentioned before, engine temp was stable and the coolant level was always good ( no low coolant warning ). This last couple of weeks the coolant temp was intermittently going above the normal mark when the engine was idling or at low speed. Thinking the worst that paulaurora had mentioned earlier, thought I'd better recheck. Turns out that the low coolant sensor on my 2year old surge tank had went south and there was no coolant in the surge tank! Argh!!. Looked around the engine and found a coolant leak at the drivers side radiator. Replaced surge tank and radiator, filled it up and..... it's been running fine since!! Heat works, cooland level is stable, no temperature clime.

Looks like I dodged the bullet this time! Thanks to all for their suggestions.

John

[Paulaurora]

what brand tank did you buy? if its doorman they have lifetime warranty they will send you free replacement.

[sempar]

Hi Paul,

I bought the Dorman one. SO far I've had good luck with their other replacement parts, though the surge tank I bought a couple of years ago has developed a sticking sensor.

John

[Paulaurora]

Than send them defectives one and they will send you new one .