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Old 12-28-2012, 01:53 PM   #1
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98 TJ Sport HVAC FAN

The HVAC fan in my 98 TJ Sport has stopped working. It has cut out and come back on intermittently over the years (once it comes back on it stays on for months, actually stayed on all summer for the AC) but has now stopped dead. Any idea where to start troubleshooting ? Relay, fuse, etc ? Thanks in advance for any help and Happy New Year !

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Old 12-28-2012, 03:54 PM   #2
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The fan gets a solid +12v to its hot side whenever the ignition switch is on. What controls the fan and actually turns it on is either a solid ground to its other side for its highest speed, or its lower speeds through resistors that are connected to ground on their other sides. I'd #1 check that it is seeing its +12 on its hot side. If it's getting that +12v, then see if it turns on by providing a ground connection to the other side with a jumper wire connected to ground. If it doesn't turn on with a ground connection and it's getting +12v to its other side, then the fan motor is bad. If it turns on, that means trouble in either the fan speed switch or the wiring between the fan, switch, and resistor pack... and that wiring commonly overheats and melts its insulation which can cause all kinds of problems.

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Old 12-28-2012, 04:57 PM   #3
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Thanks

Thank you Jerry and Happy New Year !!!!!
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Old 12-28-2012, 04:59 PM   #4
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Thank you and I wish you a safe & happy New Year too!
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Old 12-28-2012, 10:44 PM   #5
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“I'd #1 check that it is seeing its +12 on its hot side. If it's getting that +12v, then see if it turns on by providing a ground connection to the other side with a jumper wire connected to ground. If it doesn't turn on with a ground connection and it's getting +12v to its other side, then the fan motor is bad. If it turns on, that means trouble in either the fan speed switch or the wiring between the fan, switch, and resistor pack... and that wiring commonly overheats and melts its insulation which can cause all kinds of problems.”

Jerry, he has a ’98 so you are mostly correct. But on the early version that uses the slider controls rather than the 3 dial panel the circuit is essentially reversed. The ground is constant & the speed is controlled on the power (+) side of the circuit. The high speed uses the relay to bypass the resistor. On the other speeds the relay opens & current passes through various resistors depending on the speed switch setting.


Because he has lost all speeds I would think it points to a bad motor or a bad connection to the mode switch or the mode switch itself is bad.


Here is the ’98 diagram
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Old 01-07-2013, 12:51 PM   #6
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Awesome thanks

Appreciate the help and diagram !

Jim
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Old 01-07-2013, 03:49 PM   #7
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See if the diagram makes sense to you if not, post your progress & questions.

Start by seeing if you have ground & power when you should at the motor.

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