I am about to replace my 126 climate control unit for the third time. The two units shorted on the circitboard, almost in an identical spot. Why not the fuse? why the board? Why Why Why?????????

Any advise on what's going on? I can't afford too many more units. I'm seeking advice BEFORE I install the 3rd one.

There are several indivdual wires leading to the two plug /connectors. They are the obvious source for power to both sides of the unit. Should I look for unusualy high voltage? I need some expert advise....
Thanks.

Dr. Mike

You may have a motor or damper actuator (solonoid) that has a partial shorted coil winding or possibly a bad ground; causing exessive current draw. The item will appear to work, just draw more current and get a little warmer than normal.

This added draw is likely more than the traces on the circuit board can handle. If it is only a blown trace, the board should be repairable.

Has only one function stopped working? If so, then the motor/actuator (or its ground) that stopped working after the circuit was burnt is your likely cause.

If not, you need an amp meter (not volt meter) to test the current draw of the various motors and actuators. If you have several identical motors and actuators, you can test the coil resistance of each (with an ohm meter) and see which one has low resistance.

The reason a fuse hasn't blown is because the excessive current draw is too much for the trace on the circuit board to handle, but less than the rating of the fuse for the circuit.

Dr. Mike.

It's not going to be high voltage, or you would 'fry' a lot of other components.

It's going to be too much current, from a defective device or a short circuit.

For instance, a bad/shorted auxilary water pump has been known to 'fry' ACC control units.

You will need a multi-meter and a wiring diagram detailing what is connected to each pin on each plug. You can then begin to check resistance, which can give an indication through very low resistance of a possible short. You might also be able to measure current drawn by the fan motor, the auxiliary pump, the monovalve and other devices through the meter.

Hope this gives you an idea where to start.

Best Regards,
Jim

It has been recommended, in previous posts, to put a 1 amp fuse in the line to the auxiliary water pump. If you blow this fuse, you know that the pump is drawing too much current. Without the fuse, the excessive current draw fries the circuit board in the CCU.