INSTALLATION, OPERATION & MAINTENANCE INSTRUCTIONS
DEFROST SYSTEM
AIR DEFROST UNIT COOLERS: Fan motors run
continuously and a defrost time clock or low-pressure
setting stops the compressor when defrost is required.
E
LECTRIC DEFROST UNIT COOLER
: A time clock
starts the defrost process by stopping the fan and
energizing the heaters.When the defrost thermostat
resets the time clock, it de-energizes the heaters and
re-starts the fan motors.
R
EVERSE CYCLE HOT GAS DEFROST UNIT
C
OOLERS: Reverse cycle defrost systems introduce
compressor discharge gas through the suction line
during defrost. The amount of gas introduced is
controlled by a solenoid bypass valve and a gas
defrost time clock.
Condensed refrigerant is relieved through a check
valve. The check valve bypasses the expansion valve
leading to the liquid line which has reduced
pressure. The drain pan is warmed by the entering
hot gas to avoid freezing. Defrost is initiated and
terminated by the time clock.
NOTE
Minimum compressor suction superheat of 20ºF
may override these recommendations on some
systems with short line runs.
NOTE
The unit cooler must not be in operation more
than 16 hours per day.
NOTE
Using a suction to liquid heat exchanger is
recommended.
IMPORTANT
Do not use alkaline or acidic solutions; they will
damage the coils. Remove the fan guard to clean
the inner face of the fan coil.
NOTE
A field-installed pressure regulating valve may be
required on low temperature systems to control
compressor crankcase pressure.
NOTE
This method will yield accurate results as long as the
pressure drop through the unit cooler coil is low.
WARNING
If the condensing unit does not have flooded
condenser head pressure control, then the
condensing unit must have discharge pressure
above the equivalent 105ºF condensing pressure.
T
HREE PIPE HOT GAS DEFROST UNIT
COOLERS: During defrost, compressor discharge
gas is introduced in a separate hot gas line. The
amount of gas introduced is controlled by a
solenoid bypass valve and a gas defrost time clock.
To avoid excessive accumulation of liquid in the
suction accumulator, a heat exchanger is recommended. The drain pan is warmed by the entering hot gas
to avoid freezing. The time clock cycles fan motors,
liquid and hot gas solenoids.
SERVICE
INSPECTION
After one day of operation, check for any vibration
in the unit cooler. All unit coolers should be checked
at least once a month for proper defrosting. It may
be necessary to periodically change the number of
defrost cycles or adjust the duration of defrost.
Under normal usage conditions, proper unit cooler
maintenance should be done every six months to
include the following:
1. Check all wiring and insulators.
2. Check and tighten all electrical connections.
3. Inspect contactors for proper operation and
for worn contact points.
4. Check all fan motors. Tighten motor mount
bolts/nuts and tighten fan set screws.
5. Clean condenser coil surface.
6. Check refrigerant and oil level in the system.
7. Check operation of the control system ensuring
all safety controls are operating properly.
8. Check all defrost controls are functioning
properly.
9. Clean the unit cooler coil surface.
10. Clean the drain pan and check the drain pan
drain line for proper drainage.
11. Check drain line heater for proper operation,
cuts and abrasions.
12. Check and tighten all flare connections .
See troubleshooting chart for troubleshooting
information.
To properly determine the superheat of the unit
cooler, follow the steps below:
1. Measure the temperature of the suction line
at the point where the bulb is secured.
2. Determine the suction pressure in the suction
line at the bulb location by using one of the
following methods :
A
)
Placing a gauge in the external equalized
line.
B) Placing a gauge directly in the suction line
near the unit cooler or directly in the
suction header of the unit cooler.
3. Convert the pressure reading to saturated unit
cooler temperature by using a temperature
pressure table. See table # 1.
4. Subtract the saturated temperature from the
actual suction line temperature reading. The
difference is superheat.
An alternate method to determine superheat of the
unit cooler can be used :
1. Measure the temperature of the suction line at
the point where the bulb is secured (outlet).
2. Measure the temperature of one of the distrib-
utor tubes close to the unit cooler coil (inlet).
3. Subtract the inlet temperature from the outlet
temperature. The difference is superheat.
C
LEANING
The unit cooler should be checked periodically for
dirt accumulation. Grease and dust should be
removed from the fan, fan guards, and drain pan.
Occasional cleaning of finned surfaces can be done
by dusting the fins and then cleaning with a mild
detergent and warm water spray.Always pressure
clean in reverse of the air flow.