Cabin fan runs continuously but no heat or a/c?

[erikv11]

What if you just unplug the ECC unit? Easy to do, just pull the radio then pop out the ECC. Be careful, there are some sharp edges back there, wear gloves.

[Sommerfeldt]

What if you just unplug the ECC unit? Easy to do, just pull the radio then pop out the ECC. Be careful, there are some sharp edges back there, wear gloves.

+1 to that. Sounds like it's definitely your ECC gone rogue. And yeah, wear gloves - I always forget, and end up bleeding from a few knuckles every time I'm back there.

- S

[scot850]

If I recall there is a tab that needs to be pushed up/down? to release the 850 ECC unit. Gloves for this is a must!

Neil.

[a73s]

UPDATE 3
Well, bad news...go a new (junkyard) ECC and plugged that in...... and nothing. The climate control thing is still dead, no fan, nothing. Tried again to get a code from the diagnostic box in the engine and now when I plug in that probe it just glows solid red......? What could that mean?
I think I'll try to remove the blower motor and see if I can do anything with that.....
Any other suggestions are appreciated!
Thanks,

Alan.

[scot850]

As you have checked everything else, I'd pull the fan motor and see if there is a lot of movement on the shaft, and if the bearing turns easily.

If the bearings are failing the fan cage can move on the shaft and cause the bearings to lock up. As you accelerate and decelerate, the fan goes on and off.

Resistor pack is another possibility.

Finally, something most over look is to remove the 2 cabin sensors (one behind both grab handles above drivers and passenger seat, and clean them and the little fan motors up from all the junk they suck in over the years. Check if the fans spin up when you re-fit or the sensors are not registering the temperature.

It is strange the test system is not registering faults though.

Neil.

[erikv11]

Wait, in update 2 the fan was on all the time, now in update 3 the fan is never on? When did that change, what happened??

At any rate, inspecting the blower motor was suggested at the outset, it is always the first thing I do because they fail so often in these old cars, check it out for sure.

[a73s]

Wait, in update 2 the fan was on all the time, now in update 3 the fan is never on? When did that change, what happened??

At any rate, inspecting the blower motor was suggested at the outset, it is always the first thing I do because they fail so often in these old cars, check it out for sure.

Erik,
The change just happened for no reason....had a day or so of fan going on and off erratically when it was set to OFF....and now it's completely stopped.
I think I'm going to try to remove the fan and look at that tonight....I was hoping because of the time involved in dismantling everything that the ECC would solve the problem.
Thanks again for your help.
Alan.

[a73s]

Finally, something most over look is to remove the 2 cabin sensors (one behind both grab handles above drivers and passenger seat, and clean them and the little fan motors up from all the junk they suck in over the years. Check if the fans spin up when you re-fit or the sensors are not registering the temperature.

It is strange the test system is not registering faults though.

Neil.

Neil,
Yes, the diagnostic box is acting strangely (although I have no real experience with this stuff so don't really know what "normal" is!)..first it gave nothing (no light coming on) and now it gives a solid red light, and doesn't respond to any changes when I push in the black button, or hold it down for a few seconds. It IS giving codes for other things in different ports so it doesn't seem to be broken...?

Also, are the 2 cabin sensors small holes in the side of the roof above the grab handles...Do I just pry the plastic piece off and blow out the inside?
Again, thanks for your help (and everyone who's offered advice)!
Alan.

[erikv11]

...had a day or so of fan going on and off erratically when it was set to OFF....and now it's completely stopped.
I think I'm going to try to remove the fan and look at that tonight....

You will want to check the fuse, maybe it just blew, or maybe the root problem got worse.

This really sounds like a short, like a wire for the fan is frayed and rubbing and shorting intermittently to ground. And I guess it either killed the blower motor, or the wire broke so no fan circuit at all now. So that suggests two tests: (1) can you still run the blower motor if you give it 12V (e.g. take it to the engine bay and use the battery)? If so, the motor is good and you can look elsewhere. If not then you probably have two issues now, including a dead blower motor. (2) Can you ID any bad wiring? When you pull the glove box (I know, it is a hassle ...), try to inspect the wiring that leads to/from the fan.

If, on the other hand, the root problem is somehow the blower motor resistor, you may again find the motor still works. E.g. the unit finally quit altogether (but I think you would expect the fan to work OK on high). I don't know if you can test those power stage/resistor units, worth searching. Alternatively get a junkyard resistor unit and pop it in, see what happens.

Here's a couple good threads:
http://volvospeed.com/vs_forum/topic/14 ... n-for-850/ (excellent post by "Bah")
http://volvoforums.com/forum/volvo-850- ... ere-43632/

[scot850]

erik makes a lot of excellent points. PNP/junkyards are your friends here.

As to your question on the cabin temperature sensors, yes they are the small holes behind the grab handles.

If I recall you have to pull the plastic trim piece over the top of the door, remove the grab handle (I think there is a little flap hiding the screw(s) and then you can access the motor to remove it by making a gap between the headliner and the roof at the door surround.

Removing the motors gives you more access to get into it as you will be amazed at how much junk get sucked into them.

They do fail and/or when clogged up they are not sensing the ECC cannot compute what it needs to do an throws a hissy fit.

The fan is a good place to check as it is the usual suspect now that the youngest 850 is nearly 20 years old. Easy to change. The hardest part is removing the knee brace. There are only 3 nuts holding it in place although it looks like there should be 4. I think there is only 1 on the LH end. It takes some cursing to pull it down and out!

Neil.