R-Pro › Field cases › Transport refrigeration
Carrier Vector/Supra Compressor Unloader Failure
Likely causes
Unloader solenoid coil open or shorted
Check: Measure unloader solenoid coil resistance: Carrier standard 20–40Ω — OL (open) or 0Ω (short) indicates faulty coil
What to do: Always verify part number when replacing coil (12V/24V must not be mixed) → direct voltage test after replacement → verify click sound
Unloader piston seized — oil sludge
Check: Direct 12V apply test to solenoid — if no click, confirm piston mechanical seizure
What to do: Change oil and disassemble/clean unloader piston (remove sludge) → 12V test after reassembly → monitor running current
Control board unloader output fault — no 12V signal output
Check: Measure control board unloader output terminal voltage during operation — board faulty if no 12V output
What to do: Replace control board → verify unloader operation after replacement → also check refrigerant charge (compressor overload if overcharged)
Prolonged operation with faulty unloader causes compressor overheat — stop immediately and investigate if running current is 20% above rated.
All 565 cases work offline in R-Pro, with error codes for 62 brands and P-T data for 108 refrigerants.
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