740 Blower motor

I am at a loss.

I have replaced the blower motor, and replaced the BM relay. Fuse is good.
Even swapped out the AC delay relay for kicks. The motor spins slowly when
the climate control is set to vent [only after I spin to 4 and back to 0
again].

Multimeter has an odd reading in pos 4. In vent mode, about 11.4 volts.
When I spin to 1, 2 or 3, the voltage drops a tad but remains at 11.4 +/- a
few tenths. When I spin to position 4, I lose all voltage (to about .04v)

Where do I look next? Any help is appreciated.

Regards,
Tom

 

What year is your car? The motor has 1 or 2 terminals depending on
year. What happens if you put power directly on the 1 terminal type, or
power and ground on the 2 terminal type?

--
Mike F.
Thornhill (near Toronto), Ont.

NOTE: new address!!
Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

Sorry, It is an 89. The blower motor in the car now has one terminal. The
ground is screwed to the metal lip of the motor.

I did not try applying power directly to the motor. Since it was getting
the 11.4 anyway, I didnt see the need.

-Tom

 

I'm getting into the middle of a discussion so I might not know all of the
facts. However, there are three resistors that are connected in series with
the fan motor to give different speeds. You shouldn't be getting the 11.4
volts when switching between 1,2,3 and 4. I had low speed from the blower
but some times it had a horrible screeching sound. There was a small foam
gasket material that crumble away causing the blower wheel to rub against
the housing, hence low speed and noise. That blower should change speeds as
you rotate from 1 thru 4 not only in the vent positions but the other
positions as well. My car is an 86 740 but I don't think they changed.
Bill

 

Bill,

Thanks for the reply. I pulled out the resistors (three coiled springs,
correct?) and they were intact. Not sure if that even means anything.

When I spin the dial from 0, 1,2,3 and 4, I assume the voltage would top
off at 12v and spin the motor at full speed???

Could the switch have gone bad?

Sorry if these are lame questions. Trying to save a few $ at the repair
shop.

Thanks!
-Tom

 

If you're getting 11.4v at the motor then either the motor is not grounded
or the motor is bad. 11.4v is plenty for it to run.

 

I think James Sweet probably solve your problem. If you are getting the
same voltage (11.4 volts) on all speed settings and the motor does not work,
it sounds to me that you are missing the ground wire for the motor. There
are two wires; one a pinkest or lilac color that clips to motor directly and
the grounding wire that is black with a white stripe that goes to under one
of the mounting screws. When you replace the old fan motor you may have
failed to put this wire back in place. Bill

 

Bill,

Here is my original post:

I have replaced the blower motor, and replaced the BM relay. Fuse is good.
Even swapped out the AC delay relay for kicks. The motor spins slowly when
the climate control is set to vent [only after I spin to 4 and back to 0
again].

Multimeter has an odd reading in pos 4. In vent mode, about 11.4 volts.
When I spin to 1, 2 or 3, the voltage drops a tad but remains at 11.4 +/- a
few tenths. When I spin to position 4, I lose all voltage (to about .04v)

Where do I look next? Any help is appreciated.

Regards,
Tom

 

Tom. What happens if you set the unit to the defrost mode? Namely, does
the fan motor have the highest speed in position 4, then loses speed in
position 3 and so on. Or does your problem exist only in the vent mode?
Bill

 

Bill,

The problem exsists in all modes. Vent, heat and A/C.

Regards,
Tom

 

OK for all modes. But what about the speed of the motor. Does it work in
any of the 1 thru 4 positions?

 

No, it does not. When the switch is on position 0, the motor spins slowly.
At this point, the motor is getting the 11.4 volts. When I turn the switch
to any other position other than 0, the motor stops. The voltage drops a
few tenths upon switching, then returns to the 11.4 _not_ spinning the
motor.


-Tom

 

Tom everything that you mentioned sounds like a poor grounding problem.
This is my reasoning. There could be two types of motors. One that has two
wire connections and one with only one wire connection. The one with only
one wire connection has an internal wire that is grounded to its case. The
wire (lilac) connects thru the fan relay, the speed control switch, the mode
position, fuse box, ignition switch then to the battery. The motor needs
an external ground wire for it to work. In my car there is a black with
white stripe wire that gets mounted the the motor mounting flange. Make
sure that all the paint is removed before mounting. What you could do, is
take wire or battery jumper cable ground one end to say a bare part on the
car door and scrape away some paint off the fan blower assembly and see if
the blower turns. If you have 11 volts on that lilac colored wire, by
grounding that motor case or the other terminal if it is a two terminal
motor that blower should spin. Bill