Car Blower Motor Diagnostics
Blower Relay Replacement

D Vautier

Blow, bugle, blow, set the wild echoes flying


Just about all cars have a basic setup for blower motors. When the blower does not work it can be for many reasons some of which are:

1) dead battery
2) bad fuse
3) bad relay
4) bad blower motor
5) bad rheostat
6) faulty wiring

Power runs backwards with a blower motor.  By this I mean that the hot side starts out with the battery to a fuse to a relay to the motor then on to the rheostat and finally to ground as seen here:

So when the motor doesn't work start in the middle of the circuit and work whichever way you need to.  Check battery for 12 volts then apply direct power and ground to the motor from the battery since there are all kinds of other stuff on either side of the circuit.  If the motor does not run breath a huge sigh of relief because you have possibly solved what could otherwise be a very difficult problem.  All you have to do is replace the motor but first you should test both sides of the circuit.  One side should be 12 volts hot in run.  The cold side should offer some resistance depending on the fan speed dial. You don't need the car in run to test the cold side.

Now that the motor works and the hot side is hot with the ignition key on run.  If you do not get 12 volts on the hot side it's either the fuse or relay.  The fuse is easy to check.  If it's good then you have to suspect the relay which is very hard to remove and replace as I have described below.

If you do get power to the hot side in the run position then check the cold side.  Run the cold side directly to ground and if the fan works you may have a bad resister or rust.  Get your ohm gage and test the different resister positions to ground.  Number 4 should be almost zero resistance.  Further analysis of the cold side of the circuitry can be found in other places on the net. 

Testing and Replacing the  blower relay

The blower relay is hard to get to.  It is located on the drivers side under the dashboard.  There is a cluster of several relays mounted in a plastic frame and secured by a 10mm nut and a plastic gripper on the firewall.  You can locate the blower relay because it has a heavy blue wire.  Blower motors carry a lot of current and so the wires are easy to identify. 

ford escort blower motor and relay assembly unit removal

Above is a view of the bottom of blower relay assembly from under the drivers side.  You have to remove the hood release cable first with a 17mm open. 

ford escort blower motor relay assembly unit removal and install

Above I used my 10mm socket to remove the relay assembly at right.  Then I pried the plastic gripper connector away from the firewall.

ford escort blower motor relay assembly unit removal and test 

This exposed the relay assembly module.  The blower relay is the big one at the back.  Test the 5 pin relay to see if it is failing.  see "testing 5 pin relay".

My temporary solution for blower relay failure

Last winter I diagnosed this problem and decided to run a fused hot wire to the hot side of the blower because I gave up on trying to find and replace the relay.  It was too hard and too cold.  The solution worked fine as long as you remember to turn off your fan.  My son borrowed the car and got stuck a few times by leaving the fan on so I decided to do it the job the right way as described above.