ACC acting weird... Sometimes.

[Hamfist]

So, its super great that it is -7 here in VT. On the way into work, the HVAC cycled hot/cold lots. It started when my ignition switch was stuck. I have a new ignition switch, but it is still doing it.

If i turn the fan down, hit defroster, then AUTO, turning off AC, it might go to normalize. Works about 50% of the time.

What is going on?!?

[pbierre]

Sounds like all the ECC effectors are working...you're getting hot & cold and fan.

Seems like a control system problem. Either the passenger cabin temp. sensor, or the ECC software / hardware. I'd start with testing the temp. sensor (mounted under radio on console face). If you hit it with a hair dryer, does the ECC respond with colder air?

Did you try a cold restart of the entire electrical/computer system? Disconnect battery (-) terminal. Turn ignition key to II position, then reconnect battery, allowing a couple of minutes in this mode for all the computer modules to reload their firmwares.

[billr99]

Check that the wee fan in the temp sensor (behind the small grid in the face of the ECC) of the ECC is working. It can get either seized or nearly so by hairs and lint wrapped around it. That in turn does not allow enough air to flow around the sensor throwing off what the ECC is supposed to be seeing for proper heat or cold.

Cheers,

Bill

[Hamfist]

Check that the wee fan in the temp sensor (behind the small grid in the face of the ECC) of the ECC is working. It can get either seized or nearly so by hairs and lint wrapped around it. That in turn does not allow enough air to flow around the sensor throwing off what the ECC is supposed to be seeing for proper heat or cold.

Cheers,

Bill

Cool! Ill try that!

[FirstVolvo]

Cool! Ill try that!

I've cleaned that fan many of times. Here are my notes and photos that include all the things I've had to do over the years with the ECC in my car, which includes cleaning the fan and also breaking and fixing the thermistor behind the vent opening. The little fan pulls in air from the cabin and over the thermistor to regulate temp out. I mention this because while you're cleaning the fan take a look at the thermistor to make sure it's not physically damaged. It's not difficult to damage(break it in half) this device while cleaning the vent opening. If it isn't physically damaged also use the hair dryer as pbierre mentioned to check it out. This part is right behind the vent opening. Having dogs I've finally added a screen to the vent to help keep the hair out. In my car I can faintly hear the little fan running when the car is turned off and always know when it's time to clean it again.

https://app.box.com/s/8m779rkh2pdglnxtcv69nsyhmnm8x1dt