Service Manual

18
SYSTEM OPERATION
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 contactor(s)/sequencer(s) . Contacts within the
contactor(s)/sequencer(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.
*PC/*PH EEM Equipped Models Only:
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 contactor(s)/sequencer(s) and the
EEM motor. The electric heat will be energized through the
normally open contacts of the electric heat contactor(s)/
sequencer(s) . 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 34° 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 de-
frost cycle is not terminated due to the sensor temperature,
a twelve minute override interrupts the unit’s defrost period.
FAN OPERATION
Continuous Fan Mode
*PC/*PH EEM Equipped Models Only:
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/*PH14[24-60]M41*