Manual 2100-639A
Page
16 of 28
HIGH PRESSURE AND LOW PRESSURE
SWITCHES
All H**A/H**L wall mounted air conditioner series
models are supplied with a remote reset for the high
and low pressure switches. The first time the high
or low pressure switches are tripped, they will reset
automatically. If tripped a second time, reset the
switches by turning the thermostat off, then back on
again, resetting the compressor control module.
CONDENSER FAN OPERATION
NOTE: Certain models may be equipped with a
low ambient control (LAC), and if so equipped the
condenser fan motor may have a delayed start until
system refrigerant operating pressure builds up.
After starting, the fan motor may or may not cycle
depending upon ambient conditions. This is normal
operation.
The condenser fan motor on 230/208
volt, one and three phase, 60 HZ units is a two-speed
motor that comes factory wired on high speed for peak
performance. If ambient conditions permit, it can be
reconnected to low speed (red wire) for lower sound
level. See unit wiring diagram.
SERVICE HINTS
1. Caution owner/operator to maintain clean air filters
at all times and to not needlessly close off supply
and return air registers. This reduces airflow
through the system, which shortens equipment
service life as well as increasing operating costs.
2. Check all power fuses or circuit breakers to be sure
they are the correct rating.
3. Periodic cleaning of the outdoor coil to permit full
and unrestricted airflow circulation is essential.
SEQUENCE OF OPERATION
COOLING – 24VAC from MV controller at terminal 4 (Y)
pulls in compressor contactor, starting the compressor
and outdoor motor. (See Note under Condenser Fan
Operation if equipped with low ambient control.)
Terminal 9 (G) indoor motor circuit is energized by
the MV controller on any call for cooling operation or
can be energized by manual fan switch on subbase for
constant air circulation. On a call for heating from the
MV controller makes at the relay board pulling in heat
contact for the strip heat and blower operation. On a
call for second stage heat, R-W2 makes bringing on
second heat contactor, if so equipped. See Table 1 on
following page.
COMPRESSOR CONTROL MODULE
The compressor control module (CCM) is standard on
all models covered by this manual. The compressor
control module is an anti-short cycle/lockout timer with
high and low pressure switch monitoring and alarm
relay output.
Adjustable Delay-on-Make and Delay-on-Break Timer
On initial power up and any time power is interrupted
to the unit, the delay-on-make period begins, which
is the time set on the potentiometer (delay-on-break
time) plus 10% of the delay-on-break setting. When
the delay-on-make period is complete and the high
pressure switch and low pressure switch are closed, the
compressor contactor is energized. Upon shutdown
(end of the call for cooling), the delay-on-break timer
starts and prevents restart (next call for cooling) until
the delay-on-break period has expired.
During routine operation of the unit with no power
interruptions, the compressor will operate on demand
with no delay.
High Pressure Switch and Lockout Sequence
If the high pressure switch opens, the compressor
contactor will de-energize immediately. The lockout
timer will go into a
soft lockout
and stay in soft lockout
until the high pressure switch closes and the delay-on-
break time has expired. If the high pressure switch
opens again in this same operating cycle, the unit will go
into
manual lockout
condition and the alarm relay circuit
will energize. Recycling the wall thermostat or main
power resets the manual lockout.
Low Pressure Switch, Bypass and Lockout Sequence
If the low pressure switch opens for more than 120
seconds, the compressor contactor will de-energize and
go into a soft lockout. Regardless the state of the low
pressure switch, the contactor will re-energize after
the delay-on-make time delay has expired. If the low
pressure switch remains open, or opens again for longer
than 120 seconds, the unit will go into manual lockout
condition and the alarm relay circuit will energize.
Recycling the wall thermostat or main power resets the
manual lockout.
Alarm Relay Output
Alarm terminal is output connection for applications
where alarm relay is employed. This terminal is
powered whenever the compressor is locked out due to
HPC or LPC sequences as described.
NOTE: Both high and low pressure switch controls are
inherently automatic reset devices. The high
pressure switch and low pressure switch cut
out and cut in settings are fixed by specific air
conditioner unit model. The lockout features,
both soft and manual, are a function of the
compressor control module.
