Refrigeration Maintenance (Rev. 04/03)
70
NOTE: Use refrigeration compressor oil ONLY. R-134a
and R-404A systems use a special Ester oil TK No. 203-
413.
To add oil to the compressor, pump down compressor, see
“Compressor Pump Down and Checkout.”
HIGH PRESSURE CUTOUT
The high pressure cutout is located on the compressor cylin-
der head. If the discharge pressure rises above 325 psig
(2240 kPa) on R-134a units or 450 psig (3103 kPa) on R-
404A units, the switch opens the 8 circuit, de-energizing the
fuel solenoid. To test the switch, rework a gauge manifold
per illustration.
1. Connect the gauge manifold to the compressor dis-
charge service valve with a heavy duty, black jacketed
thick wall #HCA 144 hose with a 900 psig (6204 kPa)
working pressure rating.
2. Set the thermostat well below the box temperature so
that the unit will be in High Speed Cool.
3. Raise the discharge pressure of the compressor by
blocking the condenser coil air flow by covering the
roadside condenser grille with a piece of cardboard.
NOTE: The discharge pressure should never be
allowed to exceed a pressure of 400 psig (2758 kPa)
on R-134a systems and 450 psig (3103 kPa) on R-
404A systems.
4. Failure of the HPCO system to stop compressor opera-
tion should be investigated first by checking the control
circuit operation and secondly by HPCO switch
replacement.
High Pressure Cutout Manifold
COMPRESSOR PUMP DOWN AND
CHECKOUT
1. Install a gauge manifold set on the compressor. Open
the service valves (crack the valves off of the back
seated position) to access system pressure.
NOTE: Purge air from the gauge set.
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