How to use ECC wiring diagram to get heater blower running?

Mryan1776 · Post by **Mryan1776** » 07 Dec 2010, 10:15

Good morning, great site - long time reader and first time poster.

I have a 1993 850, and the ECC unit works (very) intermittently, and I'm on my 3rd ECC. I think the faults are being created by the damper motors being shot (I have disconnected the defrost / foot and passenger side damper so I can get warm air).

The blower is fine, its just not predictable...

I was able to locate a wiring diagram (http://www.volvoclub.org.uk/tech/servic ... m-Auto.pdf) and I was hoping that I could find a way to (1) add a switch to turn the blower on / off and (2) add a rheostat to control blower speed.

I read in a post that I could cut the blue wire from the blower and install a switch to ground. Is there any way to use the 3 connectors on the back of the ECC to accomplish the same thing?

Thank you very much!

Post by **BEJinFbk** » 07 Dec 2010, 10:52

No. The power and ground for the blower appear at the blower, but not at the ECC.
The ECC just signals the power stage (next to the blower) how fast to run the blower motor.
All the "heavy lifting" is done by the power stage. You'll need to make your mod there.
That's where all the high current motor wiring is.

And a "rhoestat" is not a very efficient way to go for controlling the speed of the motor.
A variable power supply rated for the motor load is probably a better way to go.
That's pretty much what the power stage is. Just controlled electronically by the
ECC instead of a "knob".

Post by **Ozark Lee** » 07 Dec 2010, 16:58

The blower motor is a power hog so if you went the rheostat route it would need to be a monster. You can simply add a switch between the blue wire and ground to toggle between off and full blast on the blower. The rheostat would need to be around 400W to handle the load if you want to go that route.

...Lee

Mryan1776 · Post by **Mryan1776** » 08 Dec 2010, 05:06

Ozark Lee and BEJinFbk,
Thank you for your information.

Now, here's the wrinkle. I live in Cleveland, and I finally put a remote start in my car. If I go the toggle switch route, it needs to stay off (because the wire is always hot) unless I'm in the car. When I remote start, the car will run, but wont defrost, until I get in the car and flip the switch.

Is there any way (using the wiring diagram), that I could use the connectors at the back of the ECC to signal the power stage only when the car is on? This way I could remote start AND get the car defrosted...

Thank you

Post by **BEJinFbk** » 08 Dec 2010, 12:45

Just install a relay.