I tore 91 S5 NA down originally to race in SCCA ITS. However, that isn't happening so I'm trying to reinstall the cabin fan. I got a half butchered harness for attaching the fan as I'd thrown mine away. When I tried everything, all I could do was choose whether to recirculate the air and turn the fan on max. The fan wouldn't work in any position but max. None of the air direction selectors cause anything to happen either. In the meantime of trying to figure this out, my heater core started leaking. So I pulled the heater core unit and the fan unit out of an S4 turbo. Put it in and now the only thing working is the recirculation button. Fan doesn't even run on max. I noticed there is another plug on the S4 turbo's fan that i don't have, so I'm wondering if that's why the fan won't work in the MAX setting anymore. I also have a big white electrical plug that is hanging inbetween the fan and the a/c box. I can't figure out what it goes to. it would be nice to get the fan running in this car so I can defog the windshield w/o a rag. What am i screwing up that's causing this thing not to work?

 

this might not be very constructive, but if I were you, I would go buy a non-butchered harness as well as matching parts for your series of car and save yourself a lot of trouble...

 

once you pull that stuff out it never works like new again, and even in good shape the blower motors are already horrible compared to other cars. in your case the blower motor never blows hard because all the ducting never fits like it used to, or not enough voltage gets to the blower because of age or wiring gremlins.

my advice is make it a race car again. Interiors are not meant to be pulled apart like that and then put back together.

 

The plug you describe is for the (not installed) factory anti-theft system. All of the contacts for the fan go through the two connectors on the right rear corner of the fan box, one multi-pin and one single pin (thats the ground)

You need to get a wiring diagram and start tracing the signals from the logicon to the fan. You can work it out, it is not that esoteric.

 

When you get the fan running, check the direction of rotation. The curved blades should be towards the direction of rotation, not trailing it. I found mine was going the wrong way, and it appears it was wired that way at the factory. Once I reversed the leads, the volume of air coming out the vents was a good 10x that which I ever got out of it before. Now it will blow your hat off. I think that many of the posts about the 'fan being weak' in these cars may be due to this issue.

 

The wiring diagram (and the rest of the factory manual) for the 89-91 RX7 is available online at http://foxed.ca/rx7manual/manuals/1989FSM/

There you can get all the pinouts for what circuits from the logicon should appear on which pins of the connector to the fan box, and verify your wiring.

 

the system on those cars is actually pretty involved, it partially runs through the factory ECU, and there is small box on the back of the logicon that also contols the fan, along with the logicon itself.

In poking around with my car we blew up the small box behind the logicon and the fan would not come on at all, never mind the AC.

 

Really?
I think the heater/defroster/fan are pretty damn good.

 

My fan works fantastic on MAX. So there's no issue of it turning backward or being weak. Unfortunately that's all it works on. I'm going to start checking through connections this weekend.

The A/C is gone now. One of the things I'm wondering is if I didn't remove an A/C relay or something that still needs to be in the system.

 

If it works on MAX, that is helpful info. There are only three wires from the logicon to the blower section. One of them identifies when the system is in MAX, and the EX-HIGH relay engages and cuts out the power transistor which is the 'speed control' at all other settings. This eliminates the 1.2 v drop which would exist across the transistor if it was left in the circuit.

That your blower works fine in max indicates that the problem may be with the power transistor, the signal from the logicon, or the wiring in between. Your symptoms indicate that the problem may be localized to just one circuit.

The FSM contains check procedures for the power transistor and the circuit that drives it.

 

I did some testing yesterday. The power transistor is in the back of the blower unit, and the missing section of my blower harness. Also tested the logicon and it failed a section.

 

What test did the logicon fail?

The variable speed function of the logicon outputs a voltage which drives the input of the power transistor. The output of the transistor drives the motor at all speeds except max. The EX-HIGH relay bypasses the resistor for max operation. If the back part of the blower assy harness assy is missing, it will not be that hard to id the circuits and make your own harness to the power transistor. As an alternative, you could pick up a blower box with the harness from a junk dealer for maybe $30 bucks. Another alternative is to pick up a motor controller kit from an electronics hobby shop and wire it in; a pulse width modulation (PWM) motor control wastes much less power than the variable resistance (across the transistor) method that Mazda used.

If it were me, I would probably just build my own harness to the power transistor. The circuit diagrams are in the FSM, though they do not provide color codes inside the blower unit harness.

That your unit works in high indicates that the EX-HIGH relay is working, as is the basic power to the unit. Apparently the only thing that is not functioning is the power transistor, or the control volage to it.

The control voltage from the logicon comes in via the 8 pin connector, G-07, at the right rear, where the front harness meets the blower harness. The color code is LO, or Blue with Orange. If you put your voltmeter on that pin and run the blower speed control up and down on the logicon, you should see a changing voltage on the meter. If it is there, your problem is in the blower harness. If not, its upstream, likely the logicon.

Keep at it...

 

The logicon failed a continuity test when using the air flow selectors.