Start-up Procedure—Heat Pump
Disconnect ALL power before servicing.
Multiple power sources may be present.
Failure to do so may cause property damage,
personal injury or death.
1. Check that the cooling mode for the heat pump is working
properly according to the procedure listed in the "Start-up
Procedure—Cooling Cycle" section.
The reversing valve is energized when the thermostat is
placed in the cooling position.
A clicking sound should be noticeable from the reversing
By lowering the temperature setting to call for cooling, the
contactor is energized.
The compressor, blower and fan should then be running.
2. After the cooling mode is checked out, turn the thermostat
system switch to "OFF."
3. Turn the thermostat switch to "HEAT" and the fan switch to
4. Slowly raise the heating temperature setting. When the
stage makes contact, stop raising the temperature
setting. The compressor, blower and fan should now be
running with the reversing valve in the deenergized (heating)
5. After giving the unit time to settle out, check that the unit is
supplying heated air.
6. If the outdoor ambient is above 80°F (26.7ºC), the unit may
trip on its high pressure cutout when on heating. The
compressor should stop.
7. The heating cycle must be thoroughly checked, so postpone
the test to another day when conditions are more suitable.
IMPORTANT: Be sure to test the unit.
8. If the outdoor ambient is low and the unit operates properly
on the heating cycle, you may check the pressure cutout
operation by blocking off the indoor return air until the unit
9. If the unit operates properly in the heating cycle, raise the
temperature setting until the heating 2
Supplemental resistance heat, if installed, should now turn
on. Check that the supplemental resistant heat operates
WGPH4549-60 has 2 stages of compressor heat. During
the resistance heat test, increase the temperature setting
until the 3
-stage heat is energized.
If outdoor thermostats are installed, the outdoor ambient
temperature must be below the set point of these
thermostats for the heaters to operate. It may be
necessary to jumper these thermostats to check heater
operation if outdoor ambient temperature is mild.
10. For thermostats with an emergency heat switch, raise the
temperature setting until the heating 2
NOTE: The emergency heat switch is located at the bottom
of the thermostat. Move the switch to emergency heat. The
heat pump will stop, the blower will continue to run, all
heaters will come on, and the thermostat emergency heat
light will turn on.
stage makes contact.
stage makes contact.
11. If the unit is being checked in the wintertime when the
outdoor coil is cold enough to activate the defrost control,
observe at least one defrost cycle to make sure the unit
Final System Checks
1. Check that all supply and return air grilles are adjusted and
the air distribution system is balanced for the best
compromise between heating and cooling.
2. Check for air leaks in the ductwork. See "Airflow
Measurement and Adjustment" and "Checking Charge."
3. Check that the unit is free of "rattles," and the tubing in the
unit is free from excessive vibration.
4. Check that the tubes and lines are not rubbing against each
other or against the sheet metal surfaces or edges. If contact
is found, correct the problem.
5. Set the thermostat at the appropriate setting for cooling and
heating or automatic changeover for normal use.
6. Check that the owner is instructed on the unit operation, filter,
servicing, correct thermostat operation, etc.
7. The previous sections are recommended to serve as an
indication that the unit will operate normally.
Explanation and Guidance—Heat Pump
When the heat pump is in the cooling cycle, the heat pump
operates exactly as an air conditioning unit.
The heat pump operates in the heating cycle by redirecting
refrigerant flow through the refrigerant circuit external to the
compressor. This is accomplished through the reversing valve.
Hot discharge vapor from the compressor is directed to the
indoor coil (evaporator on the cooling cycle) where the heat is
removed, and the vapor condenses to a liquid. It then goes
through the expansion device to the outdoor coil (condenser on
the cooling cycle) where the liquid is evaporated, and the vapor
goes to the compressor.
When the solenoid valve coil is operated either from heating to
cooling or cooling to heating, the piston in the reversing valve to
the low pressure (high pressure) reverses position in the reversing
The following illustrations show a schematic of a heat pump on
the cooling cycle and the heating cycle. In addition to a reversing
valve, a heat pump is equipped with an expansion device and
check valve for the indoor coil, and similar equipment for the
outdoor coil. It is also provided with a defrost control system.
The expansion devices are flowrator distributors and perform the
same function on the heating cycle as on the cooling cycle. The
flowrator distributors also act as check valves to allow for the
reverse of refrigerant flow.
When the heat pump is on the heating cycle, the outdoor coil is
functioning as an evaporator. The temperature of the refrigerant
in the outdoor coil must be below the temperature of the outdoor
air in order to extract heat from the air. Thus, the greater the
difference in the outdoor temperature and the outdoor coil
temperature, the greater the heating capacity of the heat pump.
This phenomenon is a characteristic of a heat pump. It is a good
practice to provide supplementary heat for all heat pump
installations in areas where the temperature drops below 45°F
(7.2ºC). It is also a good practice to provide sufficient
supplementary heat to handle the entire heating requirement
should there be a component failure of the heat pump, such as a
compressor, refrigerant leak, etc.
Since the temperature of the refrigerant in the outdoor coil on the
heating cycle is generally below the freezing point, frost forms on
the surfaces of the outdoor coil under certain weather conditions.
Therefore, it is necessary to reverse the flow of the refrigerant to
provide hot gas in the outdoor coil to melt the frost accumulation.