Testing the Defrost System

TM 10-4110-262-13&P

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Testing the Defrost System

To test the defrost system, run the unit on Cool until the evaporator coil temperature is below 36 5.4 F and press

the manual defrost switch. If the unit doesn't switch to defrost cycle, proceed to step 1 (below).

Check the Evaporator Temperature.

NOTE

The evaporator coil temperature must be below 36 5.4 F or the unit will not

defrost. Use a test thermometer to check the evaporator temperature.

1. Check the defrost termination switch.

a. Place a jumper wire between both switch terminals.

b. Press the Manual Defrost switch.

c.If the unit shifts to Defrost, the defrost termination switch is defective.

If the unit does not switch to Defrost, check for an open circuit in the 12 wire. If the 12 wire is not opened,

proceed to step 4.

4. Check voltage on PCB terminal of GR (grey) wire. If voltage is present, proceed to step 5.

5. Check for open circuit on wire GR that goes to the am-13 controller (Pin 8 C-9). If the wire GR is not open,

proceed to step 6.

6. Keeping the Manual Defrost switch pressed, check voltage on Pin 8 C-9. If voltage is present on Pin 8 C-9, and

the rest of the above mentioned points are correct, replace the Printed Circuit Board.

7. If voltage is not present on Pin 8 C-9, follow Cab Control Box troubleshooting directions.

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