Manfred

Well, with the ignition all the way clockwise, fan speed selector on high, distribution set on defrost, I don't get any power from the car side of the connector with grounding either to the chassis or the grounding wire of the connector so that would certainly lead me down one path.

On the other hand, if I jumper from the battery post to the blower side of the connector and then from the ground side of the connector to the chassis I get 12.5V (if I position my voltometer in the circuit) and yet the blower doesn't come on. That would lead me down another path.

My guess is I'm somehow not conducting the car side of the test quite right (maybe the car needs to be running?) Certainly I would think that if I'm getting 12V across a circuit that includes the blower connector then the blower should be turning.

I never did disconnect the blower during the procedure, just took out the three bolts, pulled it out and rested it on the engine.

ammonman

Disconnect the wires from the blower and perform the voltage tests recommended by Wally to make sure you don't get any voltage using the circuit ground or when using a GOOD chassis ground (engine, cross brace, etc.) If you still get no voltage using either ground when the selector is in the defrost position you need to remove the #20 fuse and see if you have voltage on the input side of the fuse (should be the top side of the fuse IIRC.)

Mike

Manfred

Yeah, that's what I did. I disconnected the connector and used the car side of the plug to do the tests (in order to eliminate loose connections as a cause of a negative test). With key in on position I get zero current from positive lead to ground (cross brace bolt). I verified my ground by making sure I was getting 12V from battery jumper post to cross brace bolt ( which I was--I actually get no voltage when using the cross brace itself, presumably since it's painted.). Again, selector switch on defroster for all tests.

I'll test the fuse box next but out of curiosity, does anyone know what affect a bad head unit would have on the voltage output to the blower? As I mentioned in the original post I did have some of the coil cleaner run back out of the center vent and tunnel behind the center console--I pulled out the head unit later ( there would have been time for it to dry somewhat) and didn't see any evidence of it being wet. Still find it strange that the blower wouldn't did turn when directly connected to the battery.

ammonman

Got it. You can't have your voltmeter in series as part of the circuit when you are applying 12VDC from the Jump post. Connect a wire from the jump post to the + terminal of the blower. Then connect a wire to the - terminal of the blower and touch the other end to a known good ground like the cross brace bolt. Hang on to the blower housing because if the wheel starts spinning it can quickly get out of control if not bolted down. The HVAC head unit set to the Defrost position causes the defrost relay to pull in IIRC. I am traveling for work this week and am away from my manuals and wiring drawings. Someone should chime in shortly with details.

Mike

WallyP

I would suggest going to an auto parts store and buying a 12 volt test light. The best type for you looks like an old-fashioned ice pick with a bulb in the handle.

Attach the alligator clip of the tester to a good bare-metal ground on the chassis - the attach bolts for the cross-brace is a good point. Touch the jump start terminal with the metal probe - the bulb should light.

With the ignition switch on, slide on Defrost, touch the metal probe to the metal inside the black wire on the car side of the blower connector. The bulb should light. If the bulb does not light, move the slide to another position (not all the way to the left), then rotate the blower switch to high speed. The bulb should light.

If the bulb does not light in any of these tests, go to the Central Electric Panel. Attach the alligator clip to a good bare-metal chassis ground. Touch the probe to the power terminals at the top of the panel - the bulb should light. Find Fuse #20 in the central electric panel. Make certain that you are on Fuse #20. Touch the probe to each of the small metal points on the face of the fuse. The bulb should light on each of these test points.

Let us know what happens.

Manfred

Thanks Wally. I'll get the bulb today but I've got a meeting I have to go to after work tonight so the soonest I'll probably be able to run the diagnostics is tomorrow. I'll post back once I've run the tests.
Dan

Manfred

OK, with the testing bulb, I get a light when testing fuse #20 but no light when I test the connector to the blower motor (testing the car-side of the connector to eliminate problems with the connections themselves). I'm thinking I must've fried my HVAC head-unit when I had some coil cleaner run back out of the center vent. I'm assuming that the HVAC head-unit controls whether there's output to the blower? Is there any way to test whether that's the case (testing input and output pins at the back of the head unit) other than swapping out the head unit and seeing if the problem corrects?

Dan

WallyP

If you tested with the lever in the DEFROST position, the head unit is not involved, except to trigger Relay XIV.

Current flow is:
Bus 30 (battery) to Fuse #20.
Fuse #20 to Relay XIV (Defrost) Terminal 30.
Terminal 87 of Relay XIV to Terminal 22 of Plug M
M22 to Connector T49 (where you were testing).

Pull Relay XIV. Use the diagram on the relay to locate Terminals 30 and 87. Test for 12 vdc on Terminal 30 in the socket for Relay XIV. If there is no power, the problem is most likely to be the connections on Fuse #20. If there is power on Terminal 30, put a temporary jumper from Terminal 30 to Terminal 87. Check for 12 vdc on the black wire in Connector T49. If there is no power, there is a problem between Terminal 87 and T49. Check Plug M and make sure that it is securely installed. Check for 12 vdc on M22 (black wire in the second terminal up on the right side of Plug M). If there is no power, the problem is behind the Central Electric Panel. If there is power, the problem is on the black wire between M22 and T49.

I'll still bet on Fuse #20...

Manfred

Wally, you're the best. So, I got 12v at terminal 30 of Relay 14 so I jumpered from 30 and 87 and then I do get 12v at T49. So, does that mean I simply need a new relay? or is the head unit not triggering Relay 14 correctly?

Thanks,
Dan

Progress being made....

ammonman

Do you get any power to the 86 pin in the relay socket when grounding to the chassis? If not then the issue is in the head unit or wiring between the head unit and the CE panel. If you get power from 86 to chassis check and see if you get power from 86 to 85. If you had power to chassis ground then no power checking to 85 ground then your problem is in the connection of the relay socket to the 31 Ground bus. If the 31 bus is open to the chassis that would explain why you get no blower response as the Fresh Air Blower Relay is also dependent on a ground via the 30 bus.

Manfred

Thanks ammomman,

Yeah, no power from the 86 to chassis ground. So that narrows my problem to either the head unit or the connection from the head unit to the CE panel.

Dan

ammonman

Check for power at fuse #37 and also check the function of the Supply Relay X. This relay powers up the whole HVAC and inside temp control system. It is powered directly off the 15 bus so it should pull in once the key is in the run position. On the 87-89 cars the relay was in position IV, but the '91 wiring diagram refers to position X.

Mike

Manfred

Power at fuse #37. Power at terminal 30 of Relay 10 with ignition off or on; power to terminal 86 with ignition on but not with ignition off--I assume this is normal behavior. So this means the head unit is probably getting the power but not passing it along to the blower through relay 14. I guess this narrows the problem to somewhere from the connection from 86 terminal of relay 10, to the head unit, then from the head unit to terminal 86 of relay 14. A betting man would assume the head unit. I guess relay 10 or 14 could still be candidates.

John Speake

Check that you haven't disturbed the connector to the head unit while working on the car.

Manfred

Problem Solved (I think). This makes twice recently where an electrical problem self-corrected in the diagnostic stages (got my reverse lights working again in the same fashion). So, I'm not sure what it was, but the last thing I did was take out the 10 relay, test it's function and plug it back in. I had to go to the store and when I fired up the engine I had full on defrost!

Best news is the problem I set out to fix is fixed (I have all four speeds functioning again thanks to the new resistor pack).

I guess if it goes out again then trying a new 10 relay would be the first place to start. I do have one more question that came out of all of this...

Is this the normal configuration for the head unit--a 944 relay stuffed back in there? It certainly looks like aftermarket wire connections...




Also, many thanks for all those that helped me work through this.
Dan