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catmastertech, Technician
Category: Construction and Road Equipment
Satisfied Customers: 2334
Experience:  Field service technician for CAT 19 years.
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I have a 2002 420D. The air conditioner and fan will only

Customer Question

i have a 2002 420D. The air conditioner and fan will only work with the fan set to high. The fan works for all three speeds when using the heater. What is likely causing this?
Submitted: 1 year ago.
Category: Construction and Road Equipment
Expert:  catmastertech replied 1 year ago.


I believe this will be related to the wiring between the blower switch and the A/C - heater switch.

I will attach a drawing of the circuit to help you trace out the wires. Wires with 100's numbers are battery + Wires with 200's numbers are grounds. 500and 600 numbers are circuit wires.

If this does not look correct to your machine, please post the full machine serial number with your reply. I will be back online tonight and can help more then.

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