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Erratic Heating

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Erratic Heating
JohnClap - 8 years ago
Hello all. I have an issue that just recently popped up. After getting up to normal operating temperature I noticed that at my usual 71 degree wintertime heat temp setting, I stopped getting heat. If I crank it up to 78 or so, I can hear the actuator open and then I have heat, for a while. If I go to 80 degrees, same thing. The Interior Sensor Fan at the side vent is working fine, but can the sensor itself go bad? Is it possibly one of the other temp sensors somewhere in the system? All the actuators are operating, so it's got to be somewhere else.
I'd be grateful for any ideas.
This happens to my car too, unless I have it set on Auto with the A/C compressor on. Using that climate control setting, the interior cabin stays at a constant heat level.
Unfortunately, when the outside temp is in the teens like it is now, the compressor automatically switches off. I wonder if the climate control is somehow out of calibration?
The heater works off a thermostat so once the cabin temp reaches (approximately) the set temperature, the air coming out of the vents will go down for a bit.
Yes, and remember the temperature sensors are not where you are sitting - depending on which model you have, you can lose a lot of heat through the top and have a cold head while the dashboard is nice and toasty. You can observe the same phenomena in the summer, where the A/C is still blowing despite having an icicle up your nose b/c the sun is shining on the dash. I consider the cabin temp to be more sort of a "guideline"

1998 986 Turbo-Look Cab 172,000 Miles Dilithium Crystal Supercharger
I have a hardtop on it, so the draftiness (?) isn't like when I just have the soft top. The heat has always worked well in the past. When I had it set at 70 degrees, it stayed around 70. Now I have to put it up to around 80 and after a few minutes the actuator closes a bit and you can feel it go colder. The cabin temp never gets anywhere near the selected temp. If I crank it all the way up to High, it seem to stay warm, but that just doesn't seem right.
Could be several problems:

1) Bad temp sensors (unfortunately don't know much about these, but you can probably find out more at the Pelican Parts board)
2) The gates in the ducts are malfunctioning - but you should be able to check this by switching back and forth between heat and A/C
3) Problems with the heat exchanger (you haven't had any coolant or engine cooling issues have you? recent coolant change?)
4) Bad head unit (again - I would assume changing successfully between heat and A/C should rule that out)

1998 986 Turbo-Look Cab 172,000 Miles Dilithium Crystal Supercharger
I think it does point towards one of the temp sensors. Everything else seems to check out. I hate to, but I may take it in and have it looked at.
Thanks to all for your help. I'll let you know how I make out.
Most of the guys who hang out there are super-knowledgeable technically and can probably point you to parts, fix, diagrams, etc. - worth finding out

1998 986 Turbo-Look Cab 172,000 Miles Dilithium Crystal Supercharger
Thanks Red, will do.
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