Blower Motor Runs Itself?

JeffersV70 · Post by **JeffersV70** » 15 Dec 2012, 11:46

Good Afternoon,

My wife and I were in the market for a second vehicle, and when we came across another 1998 V70 with relatively low miles and in fair shape for cheap money, I couldn't pass it up. I few of the problems the original owner told me about have been taken care of, but one he mentioned was that while the car was off, the blower motor would infrequently come on, and run. Over time it would drain the battery and his fix was a new battery and to remove the blower relay from behind the glove compartment whenever he parked the car. After driving the car, we forgot to remove the relay and when we came out the car started up with no problem, so I started assuming the "blower motor ghost" was in the original owners mind. That was until today when my wife came out of the store, and opened the car to find the blower running at full speed, even though the switch was set to 2. The car is a 1998 V70 without ECC. I don't think the relay is welded shut, or it would run all the time. What else should I check out?

Thanks MVS!
Jeff

Post by **Ozark Lee** » 15 Dec 2012, 12:08

While you are correct that the relay really can't be welded shut, they can stick. The relay is (in Volvo terms) inexpensive and quite easy to change. That is where I would start.

...Lee

Post by **osman** » 15 Dec 2012, 15:21

Blower motor resistor failing open?

JeffersV70 · Post by **JeffersV70** » 15 Dec 2012, 17:24

The whole system consists of the manual climate control, the resistor, the relay and the actual blower motor right?

Post by **Ozark Lee** » 15 Dec 2012, 18:07

That is how it is with my 850's that have the MCC but not so on the 70 series.

Here is a schematic of your climate control:

MCC.pdf: 70 Series Manual Climate Control.; (211.42 KiB) Downloaded 190 times

Sorry about the quality, it is a .pdf print of a scanned .pdf but it should be legible.

Based on the schematic the problem lies either with a shorted wire to the blower, shorting to battery voltage, or a bad fan speed switch in the controller itself.

I don't have any hands on experience with the manual units in a 70 series, both of mine are the electronic versions.

...Lee

Post by **JimBee** » 15 Dec 2012, 20:38

My experience is on the 850 with ECC so I don't know if this is relevant to yours.
On mine, with the key on, the hot wire to the blower motor is always full 12 volts, straight from the ignition via the relay and fuse. Fan speed is adjusted by a signal that is sent to the fist size resistor on the air box behind the glove box. The resistor changes ground continuity. So when the fan is fully on, you have a direct "return" wire from the fan to ground. You can confirm this on your car by unplugging the thick wire from the fan to the resistor and grounding it (CHECKING FIRST to make sure it isn't hot with the key on). You can do a continuity check to ground also to confirm it goes to ground.
Then if that's your configuration, when the fan is going full on even with the key off, you've got power going to its hot side when there shouldn't be any, and a connection on the resistor side of the fan directly to ground. I see those as two independent events.
Worn key switch for the power on when it shouldn't be? Bad HVAC resistor? assuming the fan setting isn't at full on when the fan gets the mysterious 12 volts.
If you can "catch it" doing its thing with the key off, try putting the key in and wiggling it to off, to see if the fan quits.