Burn-E Posted October 20, 2013 Report Share Posted October 20, 2013 So I've been encountering some erratic behavior from the blower in my 1998 S70 T5A and trying to figure what is causing it. I don't recall experiencing this with any of my other P80's. I've swapped out the ECC, the power stage and the blower motor. Symptom continues. Symptoms: Blower motor slows down or even cuts off once the car accelerates to 35-40 MPH / ~2000 RPM. Once the car slows to below 1000 RPM the fan starts to spin back up and comes to full speed once the car comes to a complete stop. The fan still blows some air so it's not completely off - usually. I'm fully aware that the AC spins down / cuts off when the car goes into boost / accelerates beyond ~3000 RPM - the AC is not on in this scenario. Settings when this happens: 1. Set the ECC fan switch to full (all the way to the right) or to Auto (all the way to left) - really any setting besides 0 but it's most noticeable when the blower is running full. 2. Set the temp switch for both driver and passenger side to anything above cold (fully turned down to the blue) or full hot (turned to red) 3. Set air circulation to outside air Settings when this doesn't happen: 1. When temp switch is to cold (fully turned down to the blue) or 2. When air circulation is set to recirculate internal air Is this normal behavior? Have I just not been paying attention previously? I usually keep the ECC set to outside air, 68 degrees, auto fan. Temp gauge in the instrument cluster is sitting right above 3 o'clock where it should be. My guess at this point is if it's not normal behavior then it's related to a temp sensor like the thermostat. Link to comment Share on other sites More sharing options...
Burn-E Posted October 21, 2013 Author Report Share Posted October 21, 2013 Slight update, it turns out the temp setting on the ECC dial is what seems to be driving the slow down of the blower. If the temperature dial is set to full heat or full cool (red - 12 o'clock or blue - 6 o'clock) then the blower remains at full blast. If it's set to anything in between the blower slows with acceleration of the engine as I described above. So what is the ECC using for temperature purposes? Trying to decide whether it's a faulty interior temp sensor (I know of 2 in the cabin and two in the ducts) or if it is the thermostat. Link to comment Share on other sites More sharing options...
Burn-E Posted October 21, 2013 Author Report Share Posted October 21, 2013 FAN CONTROL Heater (blower motor) fan speed is variably controlled by ECC output (power) stage in response to signals from ECC control module. The ECC control module digital control signals vary in length according to required fan speed. The ECC output stage has an electronic unit which receives the digital control signals and converts them to voltage. If there is no control signal or the fan is disabled, the ECC output stage sends a diagnostic signal to inform the ECC control module of the fault. If fan speed control lever is set to AUT (automatic) mode, fan speed is influenced by the position of drivers side temperature control dial, drivers side interior temperature sensor, vehicle speed, and engine coolant temperature. The highest fan speed is selected if drivers side temperature control dial is set to maximum or minimum cooling or heating. The greater the difference between the desired and actual temperatures, as sensed by the drivers side temperature sensor, the higher the fan speed. As vehicle speed increases, the fan speed will be reduced to maintain a constant airflow throughout the passenger compartment. When heating the passenger compartment after starting a cold engine, the fan speed is gradually increased as engine coolant temperature rises. http://www.volvotips.com/index.php/850-2/volvo-850-s70-v70-c70-service-repair-manual/volvo-850-ecc-climate-control-ac-heater-system-service-manual/ Hmmm, this came from the heater system service manual for the 1996 850. Sounds like it might be normal behavior but worth testing the interior temp sensor and the thermostat to confirm. May even more likely be the speed signal impulse sensor. Link to comment Share on other sites More sharing options...
Rod'sT-5 Posted October 21, 2013 Report Share Posted October 21, 2013 My fan speed only changes with the temp dial, doesn't seem to change with RPM. But I do get codes intermittently for the in car temp sensor. That may be why mine acts differently. Of course on full cold, it blows on high only. Rod Link to comment Share on other sites More sharing options...
Burn-E Posted October 22, 2013 Author Report Share Posted October 22, 2013 Thanks Rod, that helps. This is what I'm asking. Does everyone's car do this (fan speed change noticeably with RPM) or is it just my car having issues? The answer seems to be my car has a problem. Link to comment Share on other sites More sharing options...
Burn-E Posted October 22, 2013 Author Report Share Posted October 22, 2013 A couple of members over at MVS have validated my question that there is definitely something going on here that isn't normal. Questions of whether the serpentine belt or tensioner are at fault or whether a ground is failing are next steps to explore. http://www.matthewsvolvosite.com/forums/viewtopic.php?f=1&t=59689 Link to comment Share on other sites More sharing options...
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