heater fan

dez · Post by **dez** » 23 Apr 2011, 10:24

850 se 1994 I have a problem with my heater fan it started with the fuse blowing I replaced it and now the fan will not turn off with or without the ignition on Ive tried resistors relays I unpluged thm all and still the fan runs?? has anybody had this or any idea's.
dEZ

poor_volvo_owner · Post by **poor_volvo_owner** » 23 Apr 2011, 10:41

Is this "Climate Control", that is, two "Degrees" Dials vs. Manual Heat Control? Is the fan blowing HOT air full blast?

For Starters, pull the fuse to stop the fan. There's three things basically: The Box itself, the blower motor, the temperature regulator (aka Resistor or Power Stage). Climate Control BOX is likely candidate--assuming you don't have manual control.

dez · Post by **dez** » 23 Apr 2011, 11:48

thanks but its manul not climate control

Post by **vjaneczko** » 23 Apr 2011, 12:51

It's your resistor, mounted next to the blower behind the glove box.
https://www.matthewsvolvosite.com/forums ... =1&t=23749

here's the MCC part:
http://www.fcpgroton.com/product-exec/p ... control%29

Post by **BEJinFbk** » 23 Apr 2011, 15:27

How do you get resistor? If anything, it would go open, stopping the fan.
It limits fan speed for the 3 lower speeds and he's stuck on high.
That says to me that the high speed bypass relay ( 2/24 ) is the problem.
Probably fried by a dying blower motor that's pulling too much current,
or maybe just an aging relay with contacts that finally fused.

So, I'm going with fused high speed fan relay ( shown as 2/24 ) contacts.
That's the relay on the left of the two locations by the fan.
Pull that relay (2/24), it should stop the fan.
It runs off constant power via fuse # 5.
To test, you can also pull that fuse and the fan should stop.

The power feed for the resistor pack runs through an ignition switched relay, 2/30.
That's marked as relay 105 on the component location page .
So in speeds 1 - 3, it should shut off with the key.

Here are the diagram and component location pages:

94 850 MCC.pdf: (1.17 MiB) Downloaded 216 times

To check the resistor pack, does the fan run in the 1-3 settings?

Post by **vjaneczko** » 23 Apr 2011, 17:28

I had the same problem - fan running on high even with the key removed. I swapped the power stage and fixed the problem. Now I do have the ECC, but I thought they worked in the same basic manner.

Post by **BEJinFbk** » 23 Apr 2011, 22:34

Whole different ball game. The ECC has fully variable speed blower
that runs through a solid state "powerstage" controlled by the ECC.
That pack mounts in the same duct opening as the MCC resistor pack.
When fan's powerstage goes TU, it either goes open or shorts. Your's shorted.

With the ECC, you have the "Auto" option that controls the fan and flappers
based on input from the control panel, thermistors inside, outside, in the
ducts, the engine temp sensor, vehicle speed, a light sensor on the dash, etc.
That's not even getting into the A/c side of the system. Pretty Automatic.

The MCC is old school and uses a 4 speed selector switch for fan speed.
If you look at the diagrams, you'll see that the lower speeds run through
the resistor pack and there's a resistor pack override relay that kicks in
to run the blower at full-tilt boogie for the highest speed.

And instead of electronically controlled, "servo-motor" flaps,
(with the exception of the recirc flap), the MCC is all cables.
The MCC is a lot more direct. The upside? Less stuff to break!

teamSFWC · Post by **teamSFWC** » 06 May 2011, 12:17

a friend in a 97 T-5 wagon has same issue .. fan on high even with key out. changed power stage,first and failed blower motor verry soon after. I have put 2 diffrent ECC units one out of my working 850 ECC system with the same results. will not flash codes and temp controll is not working.. I have cleaned all of he damper motors as seen in a diffrent post. I did put a heater core in this car about a month befor this problem started, but it was known at the time that it did need a blower motor.