Can anyone explain this please?

Wompe1959 · Post by **Wompe1959** » 19 Mar 2025, 01:52

Can anyone explain this please?!! The blower motor sometimes works sometimes doesn’t. It’s been removed …. It works fine when 12v applied directly. New resistor fitted. There appears to be voltage arriving at the input (black and red). Even appears to be voltage leaving the resistor. In the input plug there are also a blue and yellow wires. If they are the key (from the CCU?) how can they seem to stop it working if all the above findings are true?!!

Post by **jonesg** » 19 Mar 2025, 01:58

elecs on the volvo are usually constant 12v feed, they turn on by completing the ground circuit.
You need a circuit diagram to see where the ground is switched. Maybe a relay on the CEM.

Post by **firstv70volvo** » 19 Mar 2025, 10:12

Wompe1959 wrote: ↑19 Mar 2025, 01:52 Can anyone explain this please?!! The blower motor sometimes works sometimes doesn’t. It’s been removed …. It works fine when 12v applied directly. New resistor fitted. There appears to be voltage arriving at the input (black and red). Even appears to be voltage leaving the resistor. In the input plug there are also a blue and yellow wires. If they are the key (from the CCU?) how can they seem to stop it working if all the above findings are true?!!

If the blower motor is a DC motor with brushes and a commutator, which I think it is, then it can be the motor, the brushes wear, the surface of the commutator wear and you get an intermittent bad contact point, a dead spot and the motor doesn't start. This happens to engine starter motors and why you'll hear advice to give it a good whack to get it going.

Vova585 · Post by **Vova585** » 19 Mar 2025, 10:37

Agree about possible wear in the motor contacts. If you already replaced resistor(was it blown? If yes, chances are that worn motor caused it). You would be better off paying for nissens or behr or PPS part and see if your issue resolved($120-200 range). You can chance it by used unit from ebay for around $40.

Post by **DavidE7** » 25 Mar 2025, 22:17

if the motor stops at just the right spot where there isn't good contact from the brushes to the comutator, the motor won't run until it is bumped a little out of the bad position. (Same reason for hitting a bad starter with a hammer.) I usually slam the glovebox a couple times to get it running and then plan to replace the motor and resistor ASAP. Behr has gotten very expensive but they made the OEM parts that usually last 150,000 miles+ on my Volvos.

Post by **abscate** » 27 Mar 2025, 10:44

That’s a great fleet , David. Not to mention two Nautic blues….