10
Unitary Products Group
Superheat Charging Method
NOTE: Use this method only during system maintenance and
repair.
1.
Operate system until temperatures and pressures stabi-
lize (minimum of 10 minutes).
2.
Measure and record indoor wet bulb (WB) temperature
using a sling psychrometer and the outdoor dry bulb
(DB) temperature using a thermometer.
3.
Measure and record the suction pressure at the suction
service valve port.
4.
Using Table 3, note the superheat value corresponding
to the intersection of the indoor wet bulb and the outdoor
dry bulb.
5.
With the superheat value obtained in step 4 and the suc-
tion pressure value from step 3, find the intersection of
the values in Table 4. This is the required suction tube
tempera-ture at the suction service valve.
6.
To bring the tube temperature in line with the required
value from Table 4, add refrigerant to the service port to
cause the tube temperature to fall and reclaim refrigerant
to cause the temperature to rise.
Check flare caps on Schrader fittings to be sure they are
tight. DO NOT OVERTIGHTEN (40-60 inch-lbs. maximum).
SYSTEM START-UP
ENERGIZE CRANKCASE HEATER
This unit is equipped with a crankcase heater for the com-
pressor.
A warning label with an adhesive back is supplied in the unit
installation instruction packet. This label should be attached
to the field supplied disconnect switch where it will be easily
seen. See below.
In order to energize the crankcase heater:- Set indoor two
stage cooling thermostat to "OFF" position.- Close the line
power disconnect to the unit.
SYSTEM OPERATION
See Figure 9 to trace the flow of refrigerant through the sys-
tem.
WITH POWER TO UNIT AND THERMOSTAT IN COOLING
POSITION.
1.
Reversing valve is energized through thermostat system
switch to position refrigerant circuit for cooling operation.
In the cooling cycle, discharge gas is pumped to the out-
door coil which is the condenser. The indoor coil is the
evaporator.
2.
If fan switch is in “ON” position, a circuit is made through
blower relay to provide continuous blower operation.
3.
When thermostat cooling contact closes, a circuit is
made to energize contactor and start the system, if the
compres-sor has been off for 5 minutes. There is an anti-
short cycle timer built into the defrost control requiring
the compressor to be off at least 5 minutes. With fan
switch in “AUTO” position, a circuit is made from thermo-
stat cooling contact through blower relay to provide
blower operation.
4.
System will cycle with thermostat demand to provide
cool-ing as needed.
WITH POWER TO UNIT AND THERMOSTAT IN HEATING
POSITION
1.
Reversing valve is de-energized to position refrigerant
cir-cuit for heating operation. In the heating cycle, dis-
charge gas is pumped to the indoor coil which is the con-
denser. The outdoor coil is the evaporator.
2.
If fan switch is in “ON” position, a circuit is made through
blower relay to provide continuous blower operation.
3.
When first stage of thermostat heating contact closes, a
circuit is made through the control to energize contactor
and start the system, if the compressor has been off 5
minutes. There is an anti-short cycle timer built into the
defrost control requiring the compressor to be off at least
5 min-utes. With fan switch in “AUTO” position, a circuit
is made from thermostat heating contact through blower
relay to provide blower operation.
4.
The system will cycle in response to thermostat signal to
provide heating as needed.
5.
Supplemental electric heaters are energized by second
stage of heating thermostat.
SEQUENCE OF OPERATION COOLING:
On call for cooling, the thermostat makes 24V circuits: R to
O, R to Y, and R to G. Circuit R to O energizes the reversing
valve, switching it to cooling position. Circuit R to Y energizes
the contactor, starting outdoor fan motor and compressor
(after the anti-short cycle period). Circuit R to G energizes the
indoor unit blower relay, starting the indoor blower motor.
HEATING:
On call for heating, thermostat makes circuits R to Y and R to
G. Circuit R to Y energizes contactor, starting outdoor fan
motor and compressor (after the anti-short cycle period). Cir-
cuit R to G energizes the indoor blower relay, starting the
blower motor.
Should the temperature continue to fall, R to W is made
through the second stage of the thermostat. Circuit R to W
energizes the supplemental electric heat. The field-installed
IMPORTANT
An attempt to start the compressor without at least 8
hours of crankcase heat will damage the compressor.
