Tripac APU Code 10. High Discharge Pressure.

Too much freon in the system or Condenser Fan (or 7CF fuse) is bad or High Pressure cut off switch is bad? Make sure condenser fan is spinning. If not - check 12V coming to it. If not - check 7CF fuse. If the fuse is bad, you replace it and goes bad again - probably condenser fan is shorting it. Put your hand on it (after installing new fuse and the fan spinning to see if it overhaleats).  

Check pressure (when compressor is activated) and see if it's too high (above 30-35 or above 45 during summer heat) in low pressure system  make sure condenser fan is working  it might be clogged dryer also  

Target pressure is 25-35 or 40/225 during peak summer heat. 
Component Description and Location.

The high pressure cutout switch is located on the receiver/dryer. If compressor clutch sctivated - then it's good  

How alarm is set.

HCPO switch opens at 360 psig (2482 kPa) and closes at 240 psig (1655 kPa) 

Diagnostic Procedure.

1. Check the refrigeration system for high discharge pressure and correct as needed.

2. Check the High Pressure Cutout switch for proper operation (closed under normal conditions). If it's bad then compressor won't start. Check the switch for excessive reistance. The nominal switch resistance is less than 1 ohm.

3. Check the High Pressure Cutout switch circuit as shown by Service Procedure D01A.

4. Check condenser fan and make sure it's spinning (System Monitoring tab on software will show its active), if the fan is not engaging - check 12V coming to it. If no voltage coming - check 7CF fuse on the motherboard under the bunk.