Thermo King KD-II SR, Manual

Page: 116 / 182

Refrigeration Maintenance (Rev. 04/03)
102
COMPOUND PRESSURE GAUGE
(Optional Equipment)
The suction pressure at the compressor is shown on the
compound pressure gauge. The compound gauge monitors
the low side pressure of the refrigeration system.
The compound pressure gauge should be recalibrated occa-
sionally by comparing it with a gauge of known accuracy or
by adjusting to zero at atmospheric pressure.
To recalibrate the compound gauge, pump down the unit
and pressurize the low side to slightly positive (2 to 5 psig
[14 to 34 kPa]). Disconnect the gauge line and turn the
adjustment screw on the unit gauge to bring the reading to
zero.
NOTE: If the compound pressure gauge does not stay in
calibration, replace the compound gauge.
HIGH PRESSURE CUTOUT
The high pressure cutout is located on the compressor
cylinder head. If the discharge pressure rises above 325
psig (2240 kPa) on R-134a units or 470 psig (3241 kPa)
on R-404A units, the switch opens the 8 circuit, de-ener-
gizing 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 470 psig (3241 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.
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.
1. Relief Valve (66-6543)
2. O-Ring (33-1015)
3. Adapter Tee Weather Head (No. 552x3)
High Pressure Cutout Manifold