11
13.
If unit operates properly in the heating cycle, raise the
temperature setting until the heating second stage
makes contact. Supplemental resistance heat, if installed
should now come on. Make sure it operates properly.
NOTE: If outdoor thermostats are installed the outdoor
ambient 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 is mild.
14.
For thermostats with emergency heat switch, return to
step 11. 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 come on.
15. If checking the unit in the wintertime, when the outdoor
coil is cold enough to actuate the defrost control,
observe at least one defrost cycle to make sure the
unit defrosts completely.
Final System Checks
16.
Check to see if all supply and return air grilles are adjusted
and the air distribution system is balanced for the best
compromise between heating and cooling.
17. Check for air leaks in the ductwork. See Sections on Air
Flow Adjustments.
18. Make sure the unit is free of “rattles”, and the tubing in
the unit is free from excessive vibration. Also make sure
tubes or lines are not rubbing against each other or sheet
metal surfaces or edges. If so, correct the trouble.
19.
Set the thermostat at the appropriate setting for cooling
and heating or automatic changeover for normal use.
20.
Be sure the Owner is instructed on the unit operation,
filter, servicing, correct thermostat operation, etc.
Refrigeration Performance Check
Check that compressor RLA corresponds to values shown
in Appendix B. RLA draw can be much lower than values
listed at low load conditions and low ambient condensing
temperatures. Values in Appendix B can slightly exceed at high
load conditions and high ambient condensing temperatures.
HEAT PUMP OPERATION
Cooling Cycle
When the heat pump is in the cooling cycle, it operates exactly
as a Summer Air Conditioner unit. In this mode, all the charts
and data for service that apply to summer air conditioning
apply to the heat pump. Most apply on the heating cycle
except that “condenser” becomes “evaporator”, “evaporator”
becomes “condenser”, “cooling” becomes “heating”.
Heating Cycle
The heat pump operates in the heating cycle by redirecting
refrigerant flow through the refrigerant circuit external to the
compressor. This is accomplished with 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 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 vice versa, the piston in the reversing valve to
the low pressure (high pressure) reverse positions in the
reversing valve.
The following figures 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
Summary of Contents for DTC Series
Page 18: ...18 APPENDIX B ELECTRICAL DATA ...
