The low pressure bypass timer 1TR leaves the 1TR-1 contacts
closed upon the start of a call for cooling until its 90 second
(nominal) timer has expired. This bypasses the low pressure
switch during start up. After the time delay has elapsed, 1TR-1
contacts are opened, once again allowing low pressure to
trigger the lock out circuit if the low pressure switch opens.
During a lock out, the LOR-2 contacts are closed, energizing
the X terminal on the terminal board for lighting a lock out
warning light.
Resetting the Lock Out
The lock out may be reset by:
•
Turning the thermostat switch to OFF, or
•
Momentarily adjusting the cooling set point to its maximum
allowed value.
If the unit does not resume operation after the anti-short cycle
timer expires or if it continues to lock out after resuming
operation, call a service technician to diagnose and repair the
unit.
CAUTION: Repeatedly resetting the lock out may cause
damage to the unit.
Second Stage of Cooling
The second stage of cooling will only be enabled if the first
stage of cooling is on, closing auxiliary contact 1M-AC1. A call
for cooling at terminal Y2 energizes Relay RY2, closing contact
RY2-1, and energizing time delay relay 4TR if contact 1M-AC1
is closed. If time delay relay 4TR is satisfied, it will energize its
output terminal Y2, which is connected to compressor 2 control
module terminal M1.
If the compressor 2 control module is satisfied, it will energize
time delay relay TDR. After 4 seconds, TDR energizes
compressor 2 contactor 2M.When 2M is energized on
H3CE240 units, auxiliary contact 2M-AC1 is closed, powering
terminal 2 for opening the stage 2 solenoid in air handlers which
feature a stage 2 solenoid.
550.23-TG3Y
8
Unitary Products Group
