Service Manual

SYSTEM OPERATION
19
Heat Pump Units
On a call for first stage heat, the contacts of the room ther-
mostat close. This energizes terminals R to Y and R to G,
the low voltage circuit to the contactor is completed starting
the compressor and outdoor fan motor. This also energizes
the indoor blower through the normally open contacts of the
EBTDR after a 7 second on delay on models equipped with
PSC type blower motors, and instantly on models equipped
with EEM blower motors.
When the thermostat is satisfied, breaking the circuit be-
tween R to Y and R to G, the compressor and outdoor fan
motor will stop. The indoor blower will stop after the EBTDR
65 second off delay on models equipped with PSC type blower
motors, and after the programmed 60 second off delay on
models equipped with EEM blower motors .
When auxiliary electric heaters are used, a two stage heat-
ing single stage cooling thermostat would be installed.
Should the second stage heating contacts in the room ther-
mostat close, which would be wired to W1 at the unit low
voltage connections, this would energize the coil(s) of the
electric heat relay(s). Contacts within the relay(s) will close,
bringing on the electric resistance heaters.
If auxiliary electric heaters should be used, they may be con-
trolled by outdoor thermostats (OT18-60A or OT/EHR18-60A).
Emergency Heat Mode (Heat Pumps)
NOTE: The following only applies if the unit has an approved
electric heat kit installed for auxiliary heating.
*PH Models Equipped with PSC Type Blower Motors
With the thermostat set to the emergency heat position and
a call for 2nd stage heat, R to W1 will be energized. This will
energize the electric heat sequencers. When the normally
open contacts of the heat sequencers close, this will ener-
gize the electric resistance heat and also the 240 volt coil on
the isolation relay in the control panel. The normally open
contacts of the isolation relay will close energizing the indoor
blower motor through the normally closed contacts of the
EBTDR.
*PH Models Equipped with EEM Blower Motors
With the thermostat set to the emergency heat position and
a call for 2nd stage heat, R to W1 will be energized. This will
energize the electric heat sequencers and the EEM motor.
The electric heat will be energized through the normally open
contacts of the electric heat sequencers. The indoor blower
will be energized through W from the thermostat.
DEFROST CYCLE
Package Heat Pumps
The defrosting of the outdoor coil is jointly controlled by the
defrost control board and the defrost thermostat.
Solid State Defrost Control
During operation the power to the circuit board is controlled
by a temperature sensor, which is clamped to a feeder tube
entering the outdoor coil. Defrost timing periods of 30, 60, or
90 minutes may be selected by setting the circuit board
jumper to 30, 60, or 90 respectively. Accumulation of time for
the timing period selected starts when the sensor closes
(approximately 32
+ 2° F), and when the room thermostat
calls for heat. At the end of the timing period, the unit’s
defrost cycle will be initiated provided the sensor remains
closed. When the sensor opens (approximately 60° F), the
defrost cycle is terminated and the timing period is reset. If
the defrost cycle is not terminated due to the sensor tem-
perature, a twelve minute override interrupts the unit’s defrost
period.
FAN OPERATION
Continuous Fan Mode
Models Equipped with PSC Type Blower Motors
If the thermostat calls for continuous fan, the indoor blower
will be energized from the normally open contacts of the
EBTDR after a 7 second delay.
Anytime there is a call for continuous fan, the indoor blower
will be energized through the normally open contacts of the
EBTDR, regardless of a call for heat or cool.
If the thermostat is not calling for heat or cool, and the fan
switch on the thermostat is returned to the automatic posi-
tion, the fan will stop after a 65 second delay.
Continuous Fan Mode
Models Equipped With EEM Blower Motors
If the thermostat calls for continuous fan, the indoor blower
will be energized from the G terminal of the thermostat to the
EEM blower motor.
If a call for heat or cool occurs during a continuous fan call,
the EEM motor will always recognize the call for the highest
speed and ignore the lower speed call.
If the thermostat is not calling for heat or cool, and the fan
switch on the thermostat is returned to the automatic posi-
tion, the fan will stop after the programmed 60 second off
delay on units with the EEM motor.
*PC/*PH[13-14]**H41*