j.kenzie@sbcglobal.net

Hi,
I have seen this described recently and read the postings on this topic. My system basically has two states: temp slider all the way to cold = cold; temp slider anywhere else = hot. I can hear the motor make this transition, but once the slider is off of the full cold setting and the setting motor stops, I hear nothing when I move the temp slider until I go to full cold and then I hear the flap motor moving again. The vent does indeed blow very hot, or very cold.
I can hear microswitches at the limits of temp slider.
What does this sound like? A stuck "hot" microswitch? Any ideas and ways to test would be appreciated. Since I have hot and cold air coming out I don't think it's vacuum, but I don't know. It sounds like electrical control issue to me.
Thanks

gigi02

Dave, you may want to browse through the thread called "HVAC mystery" a little further down. I had similar symptoms and it was the water valve which is not sealing well. Good luck.

85fortheDrive

Hi Dave:

Big thanks again for your help yesterday.

From what I can recall, sliding the temp control all the way to the left shuts off all heat; it means "get it as cool as possible, ignore the temperature number above me!" So that it doing what it's supposed to do. Might this situation be vacuum related? Or have you checked the heater valve? You have done wiring work around the central console, so it's possible that vacuum or electrical connections have been disrupted there... maybe?

I'll stay tuned.

Pax,
Tim

DR

Inside and/or outside temp sensor could be bad or unplugged.

Done any work in the drivers side fender well area lately?? Outside temp sensor is mounted on the inside of the front splash guard and it is common for it to get unplugged when working in this area.

85fortheDrive

What's more, it's typically attached to the alternator breathing tube.
Dave, you mentioned not having the intake tube. I'd check the temp sensor in the driver's wheel well as DR suggested. Clean and confirm connections. Easy.
(As in, I can do it )

j.kenzie@sbcglobal.net

Thanks guys. Those sound like good ideas. I will star by checking the outside temp sensor connections.

the flyin' scotsman

also the water valve; with the temp lever set to coolest it triggers the microswitch which has the setting motor go the the coolest position basically shutting of the warm air coming from the in car rad. Once you move the temp slider you may get full hot as the setting motor moves to allow some hot air but as perhaps the water valve is WFO you dont get a mix of cool and hot for a more even warmth.

as mentioned in gigi02 thread on very similar matter the auto system is a basic comparison of temp lever setting to inside car temp to outside air temp and the head unit then signals the water valve and recirc valve accordingly.

JHowell37

Check the outside temp switch as DR mentioned. I had the same exact problem on mine until I replaced that sensor.

Mrmerlin

find the thread fix you HVAC system by Mrmerlin .
It comes with pictures, it details fixing this problem by reconnecting the outside temp sensor connectors. This is the most probable source for your condition

j.kenzie@sbcglobal.net

Thanks, Stan. Great description and pics. That's my next move, probably next weekend. Thanks to all for all the other wonderful advice; it's great to have resources like the guys on this forum!

IcemanG17

Everyone pretty much covered it...but the generally accepted answer for this scenario is one of the two (or both maybe) HVAC temp senders is not working correctly....since the HVAC brain can't figure out how hot the outside air (Alt cooling duct) or inside air (on center console by glove box) is it gives up unless you override it for max cold or max heat..... Both aren't that hard to fix....with the outside being easier, since you have to move the center console quite a bit to get to the inside sensor (which is my guess)

j.kenzie@sbcglobal.net

Thanks Brian,
Since it's easier. I'll check the outside temp sensor first. I'm curious why you suspect inside sensor failure. Do you think there is a way to blow or vacuum out the sensor opening to restore function?
I appreciate your input.

Mrmerlin

to see if your inside thermo fan is working hold a lit cigarette near the grated opening (with the engine running and the HVAC system on) if the smoke gets sucked into this opening then its working, and unless you have been working on the console then you might have disturbed the connector for the temp sensor. Check outside first

the flyin' scotsman

excellent diag Stan............I dont smoke cigs but we can find something else!

jpitman2

I had same thing recently. The outside sensor was OK, but the pins and sockets in the connector had corrosion on them, all it needed was a good clean - 1/16" drill into the connector sockets, good brushing of the the pins. With the side cover off the console, you can just find the wires going to the inside sensor - disconnect the plug, put DMM across, blow into the hole, you should see the resistance change. Hope its not this one, its a console out job.
jp 83 Euro S AT 51k