850 climate control problems

rivereng · Post by **rivereng** » 03 Nov 2012, 19:39

I need your help! I have a 95 850 turbo. about a week ago I started having issues with the ecc climate control. I had no control of the blower motor (on high all the time the engine was running). auto, 0 or any variation of blower speed made no difference. At first I was getting all heat through the vents. No "flashing lights on A/C or Rec. I replaced the MOSFET "resistor pack" which is in the air duct. I still have the same symptom but now I have no heat. I pulled the ecc unit expecting to see a fried pc board. No such thing. Not even the smell of electronics that has fried. I'm an electronic technician by trade so I started checking several components that I would suspect and they all checked good. I already spent $140.00 on a new (from volvo dealer) MOSFET pack, and I would rather not spend another $100.00 or so for an ecc unit only to find it did not fix the problem. I, rather, my Volvo needs help. Winter is fast approaching and I need heat. Could it be something as easy as the thermostat? What am I missing? The "check engine indicator is but it has been on for quite some time.

nikolaj · Post by **nikolaj** » 04 Nov 2012, 05:19

If your CEL is on, I would start by having the codes read. Even if it has nothing to do with your current a/c problem, it could be something important. Further, new codes related to your a/c problem could have been added and reading them will lead you in the direction of the root cause.

I don't think your problem is related to the engine thermostat in case you have a normal reading on the dash. Could be the duovalve controling the flow of hot coolant to the heater core. If the ecc gets a signal the the coolant is warm but there is no flow to the heater core you will not get any heat to the cabin and your ecc will increase blower speed to max. These duovalves tend to stick over time and I have heard of people cleaning them with good results. I did on my SLK, where they are two solenoid activated on/off valves. Haven't had a reason to look at this on the Volvo though so can't give you any tips for this.

Another reason could be dirty/clogged cabin temperature sensors.

Just my 2 cents, hope you figure it our before it gets cold

Nikolaj

Post by **Pauloil** » 04 Nov 2012, 06:36

the resistor pack by the blower motor is likely bad. also the blower motor is old if it is original one. look at the old posts in the repair section and be sure you have replaced the correct resistor, and pull the fan and bench test it. IMHO only buy OEM replacement fans.

rivereng · Post by **rivereng** » 04 Nov 2012, 07:04

Pauloil,resistor pack is new (purchased from Volvo Dealer OEM). Cleaned cabin temp sensors, same symptom. Pulled blower fan, cleaned and lubed, same symptom. Nikolaj, dash temp gauge reads normal, thermostat was a guess and I really don't suspect it as the cause of the problem. I feel I need to restate something in my original post. When this happened, I had no fan control. It was on high and I had tons of heat. Even if the fan control was at "0" it was on full. The next day it was the same symptoms but no heat at all, that's when I replaced the "resistor pack", cleaned and lubed the blower motor and cleaned the cabin sensors. I still have the original symptom after these repairs so I'm at a loss as to what could be causing the problem.

Post by **Pauloil** » 04 Nov 2012, 15:29

ok, sorry. did you check the new thermal fuse for continuity?

rivereng · Post by **rivereng** » 04 Nov 2012, 18:42

What thermal fuse do you speak of? By the way, I never experienced the obligatory A/C and REC flashing lights on the ECC unit.

rivereng · Post by **rivereng** » 14 Nov 2012, 14:42

Replaced ecc unit from salvage yard today. Everything is working correctly. ECC unit was the problem.