Ingersoll-Rand 900829, Maintenance Manual

Page: 31 / 142

General Description
29
Defrost Mode
Defrost can be initiated any time the evaporator
coil temperature is below 36 F (2.2 C), causing
the defrost termination switch to close. Defrost is
initiated automatically by the defrost timer, or
manually using the In-Cab Control Box.
Defrost will continue until the evaporator coil
temperature rises 48 F (8.9 C), causing the defrost
termination switch to open ending the defrost
cycle. Defrost cycle can be also terminated by
pressing the On/Off Key to turn the unit off, and
then pressing it again to turn the unit back on.
Model 10 and 20 Units
When defrost is required, the controller energizes
the defrost solenoid so most of the high pressure
refrigerant vapor leaves the compressor and flows
through the defrost line, defrost solenoid, and
drain pan heater to the evaporator. There, the
refrigerant heats the evaporator and returns to the
compressor through the suction lines. Some of the
refrigerant flows through the condenser and liquid
lines to force any liquid refrigerant out through
the drier and expansion valve to the evaporator.
From which it returns to the compressor through
the suction lines.
Model 30 and 50 Units
Defrost in Model 30 and 50 units is basically the
same as Heat except the evaporator fans are not
energized. See “Heat Mode - Model 30 and 50
Units Only” and Figure 7 on page 28.
Serial Number Locations
Condenser:
Nameplate located on the back inside
wall of condenser frame.
Engine Driven Compressor:
Nameplate located
on compressor body. The engine driven
compressor is located in the truck engine
compartment.
Standby Compressor:
Nameplate located on
compressor body. The standby compressor is
located inside the condenser assembly.