1994 850 HVAC Question

rsmigel · Post by **rsmigel** » 24 Oct 2021, 10:25

Hi All,

Car: 1994 850 Turbo wagon, 200K miles, owned since 1995, always garaged, Southern car. All maintenance done by me except for transmission rebuild 5 years ago. A/C blows cold and is fully charged

Yesterday I’m driving the car in the morning, temp = 50F outside, engine temp normal, climate control set at 72, auto, A/C on, recirculation ‘off’. All of a sudden the fan goes to max and begins blowing hot air out all vents. Fan control doesn’t function and I can’t adjust temperature. Hot air blows for 15 minutes then stops on it’s own. Recirc and A/C-Off lights blink randomly. HVAC still non-functional. I park the car, turn the ignition off then restart. Everything appears then to work as normal but I didn’t check every function.

I’ve never cleared the ECC HVAC codes since owning the car so this morning I display the “B1" codes and read 25 errors. I clear the codes, pop the caps off the little fans behind the grab handles, blow them out with compressed air (not too dirty.) These little fans start spinning when the ignition key is turned ‘on’ so those temp sensors appear functional. I then drive the car for 10 miles checking all the HVAC functions. The driver’s side functions appear OK but there’s no effect on the passenger side moving the temp setting from 60–>84; no effect on automatic fan speed. In fact, manually moving the fan slider to max pushes no air out the passenger side vent, floor vent or middle/passenger vent. The recirc switch occasionally turns on the little red light above the switch but it’s not consistently working. A/C on/off switch works fine. Outside temperature display is accurate.

I park the car and re-read the codes. All I get is 1-1-1… no problem. Yet the passenger side temp and fan control doesn’t function.

I’m thinking the in-dash head unit might be bad but I need to put another hundred miles on the car and re-read the codes. Obviously, I want to systematically troubleshoot the passenger side air issues in a logical fashion and I only see myself making progress by fixing ECC error codes as they appear.

Any thoughts from the experts would be appreciated.

Post by **scot850** » 24 Oct 2021, 10:58

Can't recall if the LH and RH cabin temperature fans are interchangeable. If they are then that would be one line to try and see if the problem translates to the other side.

The other issue may be one of the servo motors has failed or the flap on the RHS of the center section of the dash has broken. It can usually be fixed with some glue and a zip-tie around the plastic section where the servo motor slots into.

If there is 100% nothing after that then it is unfortunately likely the ECC unit failed. There have been a few people who have repaired these units over the years. You may have to search to find what they did.

Neil.

rsmigel · Post by **rsmigel** » 24 Oct 2021, 16:54

Isn’t there just one big blower fan (replaced 2 years ago) with air moved around by flaps operated by servo motors? If a servo motor has failed, wouldn’t it throw up an error code immediately?

How do I access the center/right flap? I imagine it’s buried.

Post by **scot850** » 24 Oct 2021, 17:24

Yes there is only one blower fan, but the flaps are linked but also the part that fails will not throw a code as it breaks and allows the servo to move still to allow it to change position but actually the flap is not changing position.

The way to access it is to remove the lower passenger side under panel. Can't recall on the 850 if you have to remove the glove box liner or not. I don't think you do.

Once that is removed, you will be able to see the flap just tucked inside behind the center console.

What I was talking about was to try swapping the 2 cabin temp sensors over and see if that makes any change. If the RH sensor is not sensing, the RH side may not work as the ECC is not receiving a signal.

To clean the sensor, blowing wit air may not actually clean any debris out of the small fan motor. You may need to remove the sensor to actually fully clean it.

Neil.

rsmigel · Post by **rsmigel** » 25 Oct 2021, 05:14

Ah, yes, now I understand the failed flap scenario. It’s not too difficult to remove the passenger panel and glovebox so I’ll do that next weekend. I had to do that anyway to replace the blower motor and fan speed ‘resistor’ a few years back.

I still don’t understand why the blower fan speed doesn’t increase if I set the passenger temp to max or min given that the electronics can’t sense if something is mechanically broken. If the passenger thermistor behind the grab handle is faulty, it should throw up an error code.

Can someone post a pic showing where the passenger flap is exactly located? There is a rough schematic here: http://www.volvotips.com/index.php/850- ... ce-manual/

rsmigel · Post by **rsmigel** » 26 Oct 2021, 17:27

Two days later, car driven half a dozen times, no codes, no change in function.

Post by **abscate** » 26 Oct 2021, 19:17

MVS ….magical Volvo Surgery…

Post by **RickHaleParker** » 27 Oct 2021, 10:02

abscate wrote: ↑26 Oct 2021, 19:17 MVS ….magical Volvo Surgery…

Whoever calls on MVS shall be saved.

MVS Multitude of Volvos Saved.

Post by **scot850** » 27 Oct 2021, 11:47

I have to say I read the OP last note as the car is still not fixed, and still not throwing codes.

I am hoping it is MVS fixed but not sure.

Neil.

rsmigel · Post by **rsmigel** » 28 Oct 2021, 16:35

I would think that if I had a broken flapper or defective servo motor the main blower would still go to max when I turn the passenger temp to 84F or 60F. But I hear no increased airflow stuck behind the dash. If I turn the driver’s temp knob to 84 or 60 the fan blows hard.