No luck with the wipers

"MM54" (mm54mk2)
07/07/2017 at 23:33 • Filed to: RX7

Had to special order the wiper motor yesterday, picked it up today. Decided to test it out before bolting it to the linkage and installing it... it only runs on ‘high’ - no low or intermittent. Back to Autozone tomorrow.

Cleaned the weak motor’s gearbox a bunch more, it still stalls mid-swipe with the blades down. Seems to be able to handle running with one lifted up, though.

DISCUSSION (7)

Flynorcal: pilot, offshore sailor, car racer and panty thief > MM54
07/07/2017 at 23:48

Is the speed setting purely voltage driven or do you have a relay going bad? I’d think the motor would be a pretty dumb device with the logic for controlling it would be elsewhere but I’ve no experience or clue.

MM54 > Flynorcal: pilot, offshore sailor, car racer and panty thief
07/07/2017 at 23:51

The old motor that’s in there works on all three speeds (and high is indeed faster than low if the wipers aren’t touching the windshield) so I seriously doubt it’s a relay somewhere. It’s got 5 wires going to it, I’ve not gotten around to determining exactly how it works (electrically) yet.

MM54 > MM54
07/08/2017 at 00:19

Found the wiring diagram, the high vs low speeds look to be separate windings.

The 5 wires that connect to it are: one ground, two to the speed switch, one which is always hot, and the other that comes from the ‘cpu’ and is related to the intermittent mode (which uses the low speed winding). There’s a switch internal to the motor/gearbox which keeps the motor running until it reaches the ‘park’ position (this uses the ground wire from the motor, the other windings ground through the switch).

In intermittent, the ‘cpu’ (which seems to just be a timer relay) sends a pulse to start the motor, and the ‘park’ switches keep it on until it completes a cycle. In this mode the cpu also provides a ground path for the low speed winding.

In low speed, the speed selector switch simply grounds the low speed winding. In high speed, it provides a ground path for the high speed winding. In either case, when you shut it off, the park switch makes the motor continue to the end of the cycle.

Flynorcal: pilot, offshore sailor, car racer and panty thief > MM54
07/08/2017 at 00:19

One motor. Five wires....

*steps back cautiously*

Hey so wait — ground, intermittent, low, medium and high? That’s five.

You’ve got a short? Whichever wire is ground is loose? You taking out the old motor might have worked the wiring around a bit?

Not trying to make life more complicated here but I’m in a troubleshooting state of mind.

MM54 > Flynorcal: pilot, offshore sailor, car racer and panty thief
07/08/2017 at 00:23

I juuuust replied to my other comment with a breakdown of how it works haha (found the diagram in the service manual). The intermittent and low speed use the same winding, while the high speed uses its own winding - I suspect the low speed winding is bad in the ‘remanufactured’ motor, since neither of its functions work.

I put the old motor and everything back in and it all works as expected (it just can’t make enough torque to actually wipe the windshield...)

Flynorcal: pilot, offshore sailor, car racer and panty thief > MM54
07/08/2017 at 00:30

I’ll happily trade you a slightly used AC compressor for your old wiper motor

Seriously you saved me the agony of just replacing the compressor.

MM54 > Flynorcal: pilot, offshore sailor, car racer and panty thief
07/08/2017 at 00:47

Of my 3 cars, only 1 has working A/C but none of the compressors are seized! I’d like to get the A/C in the rx7 back in service, thing’s like a greenhouse.

Also for your system, depending on how it’s set up, you may want to replace the orifice tube. It’ll be a cheap little part that fits in just upstream of the evaporator. I know on the crown vic mine had a little screen on it which was clogged with crap (6 months later when the condenser leaked and needed replaced, I did the orifice tube again just for good measure, the screen again had caught a little debris the flush had missed).