Service Manual

SERVICING
110
4.5 As the temperature indoors increase, it will reach a point
where the “W2/W3” demand is satisfied. When this hap-
pens, the room thermostat will remove the 24Vac from “E/
W1” of the MBE/AEPF. The contacts on HR1 will open between
30 to 70 seconds and turn off the 1
st
and 2
nd
heater elements.
If the “Y2” demand is present and becomes satisfied the room
thermostat will remove the 24Vac from “Y/Y2” of the MBE and
the blower motor will change to 60% of the programmed cfm.
The VSTB will remove the 24Vac from “Y/Y2” at the heat pump
and the outdoor fan will change to low speed operation. The
heat pump remains on along with the blower motor because
the “Y1” demand for first stage heat will still be present.
4.6 When the first stage heat demand “Y1” is satisfied, the room
thermostat will remove the 24Vac from “G” and “Ylo/Y1” of
the MBE/AEPF. The VSTB removes the 24Vac from “Ylo/Y1” at
the heat pump and the compressor and outdoor fan are
turned off. The blower motor will ramp down to a complete
stop based on the time and rate programmed in the motor
control.
5.0 Defrost Operation
On heat pump units, when the room thermostat is set to the
heating mode, the reversing valve is not energized. As long
as the thermostat is set for heating, the reversing valve will
be in the de-energized position for heating except during a
defrost cycle.
5.1 The heat pump will be on and operating in the heating mode
as described the Heating Operation in section 4.
5.2 The defrost control in the heat pump unit checks to see if a
defrost is needed every 30, 60 or 90 minutes of heat pump
operation depending on the selectable setting by monitoring
the state of the defrost thermostat attached to the outdoor
coil.
5.3 If the temperature of the outdoor coil is low enough to cause
the defrost thermostat to be closed when the defrost board
checks it, the board will initiate a defrost cycle.
5.4 When a defrost cycle is initiated, the contacts of theHVDR
relay on the defrost board open and turns off the outdoor fan.
The contacts of the LVDR relay on the defrost board closes
and supplies 24Vac to “O” and “W2”. The reversing valve is
energized and the contacts on HR1 close and turns on the
electric heater(s). The unit will continue to run in this mode
until the defrost cycle is completed.
a. For models with defrost control PCBDM133 or PCBDM160,
a 30 second compressor delay at defrost initiation/termi-
nation is optional. As shipped from the factory, the control
is set for the delay (“DLY”), which will turn the compressor
off for 30 seconds while the reversing valve shifts to/from
the cooling mode position. To bypass the delay, which
typically reduces sound levels during defrost mode, change
the pin settings from “DLY” to “NORM”.
5.5 When the temperature of the outdoor coil rises high enough
to causes the defrost thermostat to open, the defrost cycle
will be terminated. If at the end of the programmed 10 minute
override time the defrost thermostat is still closed, the
defrost board will automatically terminate the defrost cycle.
S-50 CHECKING HEATER LIMIT CONTROL(S)
(OPTIONAL ELECTRIC HEATERS)
Each individual heater element is protected with an automatic
rest limit control connected in series with each element to prevent
overheating of components in case of low airflow. This limit
control will open its circuit at approximately 150°F. to 160°F and
close at approximately 110°F.
Disconnect ALL power before servicing.
WARNING
1. Remove the wiring from the control terminals.
2. Using an ohmmeter test for continuity across the normally
closed contacts. No reading indicates the control is open -
replace if necessary. Make sure the limits are cool before
testing.
IF FOUND OPEN - REPLACE - DO NOT WIRE AROUND.
S-52 CHECKING HEATER ELEMENTS
Optional electric heaters may be added, in the quantities shown
in the spec sheet for each model unit, to provide electric resis-
tance heating. Under no condition shall more heaters than the
quantity shown be installed.
WARNING
HIGH VOLTAGE!
Disconnect ALL power before servicing
or installing. Multiple power sources
may be present. Failure to do so may
cause property damage, personal injury
or death.
1. Disassemble and remove the heating element(s).
2. Visually inspect the heater assembly for any breaks in the
wire or broken insulators.
3. Using an ohmmeter, test the element for continuity - no
reading indicates the element is open. Replace as necessary.
S-60 ELECTRIC HEATER (OPTIONAL ITEM)
Optional electric heaters may be added, in the quantities shown
in the specifications section, to provide electric resistance heat-
ing. Under no condition shall more heaters than the quantity
shown be installed.
The low voltage circuit in the air handler is factory wired and
terminates at the location provided for the electric heater(s). A
minimum of field wiring is required to complete the installation.
Other components such as a Heating/Cooling Thermostat and
Outdoor Thermostats are available to complete the installation.
The system CFM can be determined by measuring the static