1996 850 Heater/AC is on full blast when off

Bmello1982 · Post by **Bmello1982** » 19 Oct 2015, 23:40

My heater/ac won't turn off even when in the off position. It turns off when I turn the car off but comes back on when I start the car. Any one having this problem or know how to get it to stop? Thank you

Post by **abscate** » 20 Oct 2015, 00:05

Is it just the fan or the whole AC ( compressor )?

Sounds like your resistor pack on the motor blower might have shorted...not a difficult fix.

Bmello1982 · Post by **Bmello1982** » 20 Oct 2015, 00:08

I think its just the fan. Not totally sure tho. Doesn't really feel like the ac is on

Post by **BEJinFbk** » 20 Oct 2015, 01:43

Does your fan speed control have
4 speeds (MCC) or is it variable (ECC) ?

Post by **Ozark Lee** » 20 Oct 2015, 08:19

There is a 99% chance it is an ECC and the power stage shorted out. On the ECC battery power is always there at the fan, even with the key off, and the power stage modulates the fan speed by changing the duty cycle to ground. When it shorts out the fan will not turn off.

They are expensive so you need to make sure the fan itself is OK. If the fan growls or squeaks the blower needs to be lubricated before you change the power stage to prevent damage to the replacement. The power stage on the ECC is analogous to a blower resistor but it is a solid state device.

...Lee

Bmello1982 · Post by **Bmello1982** » 20 Oct 2015, 12:37

It does not have 4 speeds. So I guess its an ECC. Is there anyway I can disable the fan temporarily till I have time to figure out more about it?

Post by **abscate** » 20 Oct 2015, 12:43

You can pull the plug out of the back of the fan which will stop it.

Bmello1982 · Post by **Bmello1982** » 20 Oct 2015, 13:29

I'll try. Thank you

Post by **abscate** » 20 Oct 2015, 15:55

Complete DIY with pictures here...

https://www.matthewsvolvosite.com/forums ... =1&t=19322

Thanks to Mod Ozark Lee....

Bmello1982 · Post by **Bmello1982** » 20 Oct 2015, 17:00

Thank you for all the help. Gonna try that. Is there a fuse I can pull out just to get it off for the short term?