Help, A/C blower motor won't turn off

I have a strange problem in my 94 Grand Cherokee Limited. The other day I turned the car off and the a/c blower motor (fan) kept running even after I took the key out. I had to pull the fuse to shut it off. The a/c and heater seem to work ok, it's just that the fan won't turn off. I took it to a local mechanic who said I need a new HVAC control head. The dealer has to order it, and it costs $700! Can it really be that big of a problem to fix a blower motor that won't shut off? I'm now popping the hood and putting the fuse in before I drive, then pulling the fuse when I'm done. For $700, I'm thinking of building some kind of switch that runs from the fuse to outside the hood so I don't have to pop the hood. Any ideas?

Reply to
np6
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Ummm...

Maybe the sensor has failed?

Try a multimeter on it to see if it has a connection when cold, if so replace it.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

np6 wrote:

Reply to
Mike Romain

np6 did pass the time by typing:

Tell the mechanic to get bent. :)

From your description and the base Limited, prolly the auto. So let's start there.

I'm betting you have a stuck blower motor relay. That's the most likely failure point.

Problem is I think the relay is in the control head. Should be real close to the fan speed switch. Follow the trace back from pin 4. Give it a good thwack with a mallet.. er.. tap it a couple of times it might free up.

This schematic is very poor on that module, it almost looks like a replacable 5 pin style relay, like a fog relay.

My scanner is down, but if you want the schematic just post a reply with "DougW" in the subject line and I'll catch it easier.

Reply to
DougW

Approximately 9/24/03 15:38, np6 uttered for posterity:

The blower motor is controlled by the ATC controls with speed feedback. You may want to disconnect the battery as it resets the control completely. This *could* be as trivial as the high speed relay.

With the fuse in, turn it on, then turn the motor off. Then pull the A/C fault codes.

Push AC and RECIRC at the same time. While doing this, rotate the Temp knob one click Clockwise. This should light all indicators as long if you keep your fingers on the AC/RECIRC.

Take your fingers off the AC/RECIRC and the display should go to 00, ready to pull codes. Push *either* the AC or RECIRC but not both. The little stickman appears indicating you are now in Diagnostic Mode. If the display stays at 00, the thing doesn't *think* the ATC module is bad. Push the same button AC *or* RECIRC to step codes.

If you see fault 25 or 29, the ATC is bad and the rest of any codes are bogus. Code 08 would indicate motor feedback is too high, possibly not the ATC. 12 means the fan control knob is bad. 16 means not enough motor feedback.

40 means at some point the feedback was too high but not at the present. 48 is historical feedback too low. 61 means the ATC was bad but thinks it is ok now.

To clear codes, push AC *or* RECIRC and hold for 3-4 seconds until 2 bars appear on the display. Only clears codes 33 and higher.

You can pull detailed status by starting all over, push AC and RECIRC, one click CW. This should turn on the stick man and set to 00 or an uncleared fault code.

Step the tests by rotating the knob CW. OC is open ckt, SC is short.

As you step the display with the knob, to read the inputs, press either AC or RECIRC.

To actually test the outputs, go back to Diag Mode with the AC/RECIRC trick and one CW click.

Then select the test you want to run by turning the Temp Knob CW and when it displays the number you want, push the AC button to see the result.

Test No. What is checked Display ------- --------------- -------------------------

01 Blower Ctl Switch ?, OC, SC, 00-255 02 Blower Feedback ? 00-255 03 Blower Speed 00-255 04 Hi Speed Relay 00= off 01= on

If you push the RECIRC button during these, the value will step and the motor should speed up/down.

And your warranty on this advice is roughly the same as you paid for it.

Reply to
Lon Stowell

Approximately 9/24/03 15:55, DougW uttered for posterity:

Note that this relay ain't thar unless the unit has ATC. And caution that this is from a 95 FSM, so YMMV. Fuse 11 goes to the high speed relay. If the relay is on, it feeds a full battery voltage to the motor. If the relay is off, the motor speed is controlled by battery voltage being fed to the motor thru the Blower Power Module, which could also be bad. Variable speed is controlled by the BlowerPowerModule which gets its feed from the ATC controller.

The Blower Power Module is allegedly along the right side of the Instrument Panel, fairly near the Auto Temp Controls on that panel.

The High Speed relay is located along the right hand side of the HVAC under the dash. It gets a one-line feed from the Auto Temp Controller.

Unfortunately neither the FSM nor the Body Diag has any better location info or pictures or even remove and repair for those two items.

Reply to
Lon Stowell

Reply to
L.W.(ßill)

L.W. (ßill) Hughes III did pass the time by typing:

That's the relay.. It shows in my service book like a relay on the control head but the numbering indicates a much larger relay that would be mounted to a board. The numbering in that diagram matches and I'm fairly sure the guts didn't change from

93-95. Only some minor things like 4wheel disc brakes.
Reply to
DougW

Reply to
L.W.(ßill)

Approximately 9/24/03 18:08, DougW uttered for posterity:

Bill's picture exactly matches where the FSM says it is.... so swap that sucker. From the wiring diagram, if you can get your hand in there it should be possible to just pull the sucker to test, since if you have ATC [which we forgot to ask] the only thing that relay does is kick in high speed, aka full battery voltage.

Reply to
Lon Stowell

You guys are a wealth of information, thanks a lot. Oh, my Jeep does have ATC, I forgot to state that. Unfortunately, I tried the various suggestions and I still have the problem.

I disconnected the battery and reconnected it, but the problem is still there. I also tried to find the relay and hit it lightly. Not sure I actually found it, but nothing I hit made any difference.

I followed your detailed instructions (thanks) and this is what I got: Code 08 and 48.

I then did the output tests you mentioned and this is what I got:

Test number 01 display 11 Test number 02, display 28 Test number 03, display 28 Test number 04, display 00

I then pushed the RECIRC button and the fan did speed up/down.

This is greek to me, but maybe it will tell you something.

I did see a fat juicy red wire going into the blower motor, just under the glove compartment. I'm tempted to cut that and put an online switch there, but when I mentioned this to the mechanic he said I could produce a voltage spike that might screw up the computer that controls everything and costs $2000. So, I'm hesitant to do anything there but still thinking about putting a switch in place of the fuse under the hood, that might be a safer thing to do.

I just hate paying $700 to turn off a #%@^$ fan. Just last month I took it in to repair the CV joints, and they replaced both axles for $800, which I was told was actually not too bad, but now for about the same price I get to turn a fan off. Go figure.

Reply to
np6

Approximately 9/25/03 08:01, np6 uttered for posterity:

08 means the feedback from the motor is too high which is wierd unless there is a typo in my FSM, as it claims 48 means that at some time in the past it was too low.

Purely a WAG, but if that relay was shorted or the power control module was fried, I would expect solid fan speed and probably an error because the commanded speed wouldn't match the actual speed. Real jeep mechanics feel free to jump in any time here...

I'd pull the relay if you can...

speed blower relay is off...]

Hmmm. So whatever is wrong is such that the fan can be controlled. To me this would eliminate the relay, but I'd still pull it just because I am such a sceptical cuss.

And it looks like the power controller may indeed be able to change the amount of battery voltage available to the motor.... unless it is interacting with the high speed relay which is easily checked by yanking the relay.

If the fan speed is still changeable, either the power control module has a blown position in it [dunno likelihood] or the output of the ATC module is tweaked, or the motor itself has a bad feedback pickup, causing the ATC to freak out.

To narrow it down, the only way I can see is to get under there and check the voltages at a coupla points from the ATC to the motor and back... after pulling the relay of course.

I actually bought the extended warranty [from a competitor yet] on a used ZJ on the recommendation of the service manager at the Jeep dealer [the ZJ itself was bought elsewhere] when he told me how much it typically costs to make repairs on the air conditioner, seat controls, etc. compared to the more reasonable prices for running gear repairs. Worse than a darned cadillac.

Reply to
Lon Stowell

Having messed with a '93 Taurus with ATC, I'll never own one again. Simple switch and resistor pack for me.

On topic, I'll bet it's the motor speed feedback, since it did slow down during test and popped that code. I wonder if that's replaceable, without changing the blower. __ Steve .

Reply to
Stephen Cowell

After considering all the alternatives suggested on this board, I went to a different mechanic (factory guy) and was able to talk with him more intelligently about the problem. He diagnosed it as a bad blower motor resistor, part #4720046. He replaced it for $127.05 parts and $77 labor. And I thought only Uncle Sam would pay $127 for a resistor. Imagine if it would have been a capacitor. Better than the $700 the other guy wanted to charge to replace the entire HVAC control head.

Thanks again for all your advice.

Reply to
np6

Approximately 9/26/03 13:31, np6 uttered for posterity:

Parts is expensive, but on the ATC system, I'd be very surprised if that motor resistor pack wasn't in the speed feedback chain pretty much as the diags showed.

Reply to
Lon Stowell

With continuously variable speed blower, it's not a simple resistor pack... more like a speed controller, like the robots on Robot Wars use. $127 sounds a *lot* more like a speed controller module than nichrome wire coils and a thermal fuse. That's what my '93 Taurus LX (POS) used... now an obsolete part. __ Steve .

Reply to
Stephen Cowell

replying to Lon Stowell, 96JeepOwner wrote: I know this makes no sense, but it is the blower resistor. Yes, I know it doesn't compute that a bad resister would deliver power to the blower with the key off and out of the ignition. My 96 Grand had the same issue and I figured it must be the relay (behind the glovebox on the end of a cable) - but swapped that out and it made no difference. I presented the problem to the Jeep Dealership mechanics ( 3 in the shop at the time) and they were stumped - suggested the 'electrical diagnostic test' at $135 for the first hour. Well, I bought the $200 Mopar resister and TaDa - everthing works perfectly.

Reply to
96JeepOwner

replying to np6, miner_aaron wrote: im have the same problem with a 1994 jeep grand Cherokee limited

Reply to
miner_aaron

replying to np6, miner_aaron wrote: im have the same problem with a 1994 jeep grand Cherokee limited

Reply to
miner_aaron

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