'96 850 Heating and AC Problems

JonTechno · Post by **JonTechno** » 28 Jan 2019, 06:39

1996 Volvo 850 2.5L Automatic.

Heating and Air Conditioning unit stopped functioning over night. Oddly enough, if I press down hard on the Fan Speed Selector Switch, on Speed Setting 1 or 2 only, the Blower Motor turns on to blow out desired air temperature. But I have to keep the selector switch depressed. If I let go, it turns off. Fan speeds 3 and 4 don't activate no matter what I do.

Thinking I may have to replace the entire unit, but I wanted to first check here and make sure I've considered all the options.

Any suggestions appreciated

Post by **scot850** » 28 Jan 2019, 15:00

Chances are the switch has gummed up or has failed. If you have the ECC unit it is easy to swap out if you get one from the junkyard. It may be a combo issue you may also have a power resistor issue too. If you have an MCC (it won't say Auto on the panel anywhere) then it may be the switch.

Neil.

Post by **BEJinFbk** » 28 Jan 2019, 19:16

Speeds 1,2,3 & 4 indicate that you have MCC (Manual Climate Control).
I agree with Neil - Sounds like your fan speed control has packed it in...

Klausc · Post by **Klausc** » 29 Jan 2019, 11:35

Find a new unit at a junk yard or pick&pull. It might be possible to tear your unit apart and repair the switch, but that would take quite some time and I am sure you want heat tomorrow.

Post by **BEJinFbk** » 29 Jan 2019, 13:06

One could override the speed 4
full voltage relay to get heat for now.

JonTechno · Post by **JonTechno** » 29 Jan 2019, 13:08

BEJinFbk wrote: ↑29 Jan 2019, 13:06 One could override the speed 4
full voltage relay to get heat for now.

How would one go about that?

Post by **BEJinFbk** » 29 Jan 2019, 13:54

The gist of it is that high speed (4) has
a relay at the blower motor that totally
bypasses the resistor pack and just puts
full voltage right to the blower motor.

Fortunately, this isn’t a new topic.
More info and further details can be found here:
viewtopic.php?f=1&t=86151&p=478938&hili ... ay#p478938

Stay Warm!

Cookeh · Post by **Cookeh** » 29 Jan 2019, 14:21

Sounds like the resistor to me, as to my knowledge that's the only thing controlling blower motor speed is the resistor. These are easy enough to fit and pretty reasonably priced.

Here's a link to what is potentially the same problem by another poster on this forum:

click me

Post by **BEJinFbk** » 29 Jan 2019, 19:59

Cookeh wrote: ↑29 Jan 2019, 14:21 Sounds like the resistor to me, as to my knowledge that's the only thing controlling blower motor speed is the resistor. These are easy enough to fit and pretty reasonably priced.

Here's a link to what is potentially the same problem by another poster on this forum:

click me

Not true. If the MCC fan speed selector switch is bad,
power doesn't even make as far the resistor pack.
And from the description given by the OP, there's
something hinky going on with that switch.
It should crisply snap from position to position
with no additional wiggling or pressure involved.

Sure, the resistors may have also "reached the
end of their broadcast day", no doubt, but beginning
with that sketchy switch is the first move that I'd suggest.

It's all in the wiring diagram:

95 850 MCC Wiring Diagrams.pdf: (450.04 KiB) Downloaded 214 times

Cookeh · Post by **Cookeh** » 30 Jan 2019, 02:32

BEJinFbk wrote: ↑29 Jan 2019, 19:59Not true. If the MCC fan speed selector switch is bad,
power doesn't even make as far the resistor pack.

Thanks, always good to learn!