Heater temp & fan stuck on high

jminor12 · Post by **jminor12** » 20 Oct 2016, 16:38

I have a '94 Volvo 850 turbo, & I can't adjust or turn off the heater. It was in the off position, & all of a sudden it comes on full blast & a bit of smoke came out of the vents. It only turns off when I turn off the vehicle, & it won't allow me to adjust the settings. Any help?

Post by **Ozark Lee** » 20 Oct 2016, 16:45

Is this an electronic climate unit or a manual unit? They look very similar but the electronic version has AUT positions and the temperature settings are in degrees. The manual unit has fan speed settings 0 to 4 and the temperature settings are graduated width colored bars.

The way the fan speed works is very different between the two so we need to know which one you have.

...Lee

jminor12 · Post by **jminor12** » 20 Oct 2016, 17:17

I guess it would be an electronic unit then. It has temperature settings for both the driver & passenger, & fan speed is controlled by a sliding bar.

Post by **dyn blin** » 20 Oct 2016, 21:22

Others will post some time-saving trouble shooting tips. My personal experience of that behavior in 2 of our 3 P80s with ECC has been the blower motor resistor, part # 9144354. They're pricey, so a testing of all the components is worthwhile before you buy a part that may or may not remedy the problem. A comprehensive resource is here:

Pre-OBD2 850 ECC Troubleshooting

Post by **Ozark Lee** » 20 Oct 2016, 22:48

If it is an ECC then pull the codes from port B-1 and post them back. Usually when the power stage (blower resistor) shorts out then the fan won't even turn off when the key is turned off since it is powered all the time. The early ECC units are particularly prone to shorting out the capacitors and burning a hole in the circuit board. That is easy to spot by removing the controller and then just taking the top off. A bad one is immediately obvious with the soot on the inside of the cover and the charred components.

...Lee

jminor12 · Post by **jminor12** » 24 Oct 2016, 16:28

The B-1 port unfortunately didn't give me back any codes. So when you say take off the controller, you want me to remove the ECC (as in the whole control panel?) & look for soot & charred components? Sorry, I'm not very car savvy.

Post by **Ozark Lee** » 24 Oct 2016, 17:40

That is the next step, if indeed it is an ECC. If there is a chance that it is a MCC, the one that has no AUT settings then it will be extremely difficult to remove and you really shouldn't try.

To remove the ECC first remove the radio, you don't really need to unplug it from the wires, just get it out of the dash. If you unplug the radio you need to have the anti-theft code to enter when you plug it back in or it won't work. If you can avoid unplugging the radio then it will make things easier.

To remove the radio look for the rectangular tabs next to the preset buttons on both sides. They are, give or take, an inch long and about 1/8" wide, oriented vertically. Use the key or a screwdriver and press in on the tabs and they will pop out and reveal a couple of pull tabs. Just use the tabs to pull the radio out of the dash. There isn't a lot of extra wire so it just dangles in front of the shifter.

Once the radio is out reach up through the radio slot and push the climate unit controller toward the back seat and it will pop free. There are a couple of electrical plugs on it and you should go ahead and unplug those and remove it entirely.

From there just take the screws off of the cover and see what you can see. When they go bad it is obvious.

If you discover that you have a Manual unit then your problem makes much more sense and it can be traced to a stuck Max Fan relay. Replacing that relay is real easy but getting to it can be a challenge and it usually requires removing the glove box to gain access where you can see it.

...Lee

Post by **scot850** » 24 Oct 2016, 19:39

Not sure if it helps, but this is a picture of a Canadian ECC unit. The only difference with a US one is it reads in degrees Fahrenheit on the 2 outer dials. If you have an MCC unit it has I think red and blue strips in a circle where the ECC has the degree numbers. Also if you look at the lower LH of the front face of the ECC unit picture you will see the 'AUT' - 0 - then the variable speed slider. The MCC unit does not have this AUT feature.

: ECC unit from an 850

The MCC is a pig to remove as it has manual cables attached to it, but the ECC is fairly straight forward as Lee has explained. I suggest wearing gloves as there is a metal spring under the middle of the ECC unit that needs to be moved to allow the unit to be pulled out. Lots of jaggy bits in the radio space so be warned!

Neil.

GarryD · Post by **GarryD** » 08 Nov 2016, 09:44

Hello,

I would love to hear back from JMinor if this was resolved. I'm having the EXACT same problem, but I seem to have a problem with the diagnostic system, it won't pull any codes for B1.

Like I mentioned, sounds very similar. Blower only on when key is in ignition position. Blower on high. The ECC seems dead, nothing changes in response to working the controls. I don't think any dampers move. I removed the ECC and took the cover off. There are 2 boards inside, I didn't see anything that appeared to be burned out, but I'll take a closer look later. I will look closely at BOTH boards, not just the top one as well.

If this is a bad ECC, then that would be a much easier repair, just swapping units. I'd love to avoid taking out the blower motor if possible.

Thanks,

-Garry