1994 850 turbo help de-bugger my A/C

cracker red · Post by **cracker red** » 09 Oct 2014, 18:03

Apparently something on the AC broke with the previous owner. What they have done is bypass the climate control completely with a single pushbutton switch. This runs the fan on high and the AC comp on. I assume because the climate control unit broke and they thought saving $50 on a used on was too much trouble. But I digress...

The harness is intact save for one wire/lead, what I assume is the compressor clutch signal. The pushbutton switch supplies power to it and the fan. Fan only runs on HIGH when the switch is depressed.

I have installed a used EEC unit. The flappers all work (can change floor/defrost, etc), the recirc button seems to function, and I can even turn on the heat....However the fan will not function (unless the pushbutton switch is on to activate the fan) and the AC clutch will not engauge (with the harness repaired at the EEC).

What do I check/trace down next?

Post by **Ozark Lee** » 09 Oct 2014, 19:07

What you need to do is undo what was done to bypass the ECC in the first place. There is no instruction set for that since mans ability completely butcher a wiring harness is nearly limitless. The place to start is to first download the factory service manual from here:

https://www.matthewsvolvosite.com/downlo ... vo_850.zip

After you unzip it you can either go to the file named System Wiring Diagrams.pdf or AC Heater System Auto.pdf and print off the schematics for the ECC system. This will give you the wire colors and make things easier to trace.

The climate unit is not as horribly complex as it seems when it comes to the AC part and the connector pinout numbers and the wires colors should get you from point A to point B for the factory design. The place to begin the actual delousing procedure would be at the switch that was added and see where the wires go.

Once you get the wiring patched back up it is fairly easy to follow the voltage flow from the ECC controller module to the AC relay and through the low pressure switch, looking for a circuit interruption along the way.

The cabin blower motor is controlled by the ECC controller through a solid state "blower resistor" that is called a power stage. It isn't uncommon for that power stage to fail and cause the cabin blower fan to fail.

Once things are wired properly you can use the diagnostic code reader to pull error codes from the under hood OBD-I port and figure out the rest of the problems fairly easily.

...Lee

cracker red · Post by **cracker red** » 09 Oct 2014, 21:08

Will report back after I hunt around in the car. Only one wire was clipped behind the EEC, as far as I can tell it's the signal wire.

I'll have to dig on the blower resister further....the fact that I have no fan control and it runs on high only perhaps means it's been either rigged or jumped to just RUN....maybe why I have no fan control.

At least the AC does in fact work, and work well. Now to get it working through the EEC as designed and I'll be that much closer to having a nice daily driver instead of the basket case.

Still can't complain for $1400

cracker red · Post by **cracker red** » 14 Nov 2014, 12:40

I didn't want to tear into the car in the summer for fear of having NO A/C at all, but today (now that it's cooling off a bit) took the plunge.

Previous owner apparently had a bad ECC. The blower resister was jumped with a relay to ground, and the AC compressor wire was also in the mix which caused the AC to come on fan to come on high. Yeah...it worked but swapping in a used EEC would have been easier me thinks.

Soldiered up the cut wires, put the used ECC back in place. Whala....I now have fan control using the slider and the AC comes on as it should.

PROBLEM....the "AUTO" portion of the fan selector switch seems to have no effect at all. I'm happy it's much better than before...but I'd like it to work 100%

Thoughts?

Post by **scot850** » 14 Nov 2014, 17:51

There are 2 small temp sensors (if memory serves) on an 850 up under the grab handles above the driver and passenger doors. These get gummed up over time. Remove them and give a thorough clean and a little lube. It will probably be fine after that.

Neil

cracker red · Post by **cracker red** » 17 Nov 2014, 13:24

I cleaned the temp sensors but no change. The auto TEMP seems to work fine....its the AUTO FAN CONTROL/speed that doesn't work when it is on AUTO.

Post by **scot850** » 17 Nov 2014, 13:53

Have you checked the a/c using the system checker under the hood? Have you got any codes when you do this? There are alot more smarter guys on here who can correct me if they wish. The system is not too difficult, but I think you have checked most items, but I think the resistor pack may be the issue. I would think the slider portion controls fan speed with a rheostat function, whereas the Auto function uses the resistor pack to `automate` the fan adjustment. Although you have cleaned the cabin sensors, it does not mean the are operating.

Neil.

cracker red · Post by **cracker red** » 17 Nov 2014, 18:37

I will scan it and report back. After replacing the ECC and clearing the codes I didn't get another one.

The AC/Recirc buttons arn't flashing either.

Post by **Ozark Lee** » 17 Nov 2014, 21:26

Given the history that you have described there are likely a bunch of error codes stored. Read all of the codes, you may want to write them down as they flash out, and then erase them. At that point you will know that any subsequent codes that you read after trying the system again are real and relevant.

This will be a two part process, the first part is to erase the history and the second part will be to gather the codes that are current. The latter codes are the ones that will indicate your current problem.

...Lee