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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
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 reenergize 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 resets the manual
lockout.
Low Ambient Control
The fan cycling control cycles the fan motor on once
the liquid refrigerant pressure reaches 350 psig, and
off once it has dropped to 225 psig. It will continue to
cycle between these parameters depending on outdoor
temperatures and the load/stage of the system.
This cycling maintains a minimum liquid pressure
affecting the minimum suction pressure. This effect
ensures an evaporating temperature that is slightly
above the point of ice formation on the evaporator.
Alarm Relay Output
Alarm terminal is output connection for applications
where alarm relay is employed. This terminal is
powered whenever 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 or heat pump unit model. The
lockout features, both soft and manual, are a
function of the compressor control module.
Adjustments
Adjustable Delay-on-Make and Delay-on-Break Timer
The potentiometer is used to select delay-on-break time
from 30 seconds to 5 minutes. Delay-on-make (DOM)
timing on power up and after power interruptions is
equal to 2 minutes plus 10% of delay-on-break (DOB)
setting:
Manual 2100-646
Page
16 of 26
0.5 minute (30 seconds) DOB = 123 second DOM
1.0 minute (60 seconds) DOB = 126 second DOM
2.0 minute (120 seconds) DOB = 132 second DOM
3.0 minute (180 seconds) DOB = 138 second DOM
4.0 minute (240 seconds) DOB = 144 second DOM
5.0 minute (300 seconds) DOB = 150 second DOM
During routine operation of the unit with no power
interruptions, the compressor will operate on demand
with no delay.
Typical Settings for Dual Unit Installation:
Unit 1: DOB set at 2 minutes and DOM is 132 seconds
Unit 2: DOB set at 4 minutes and DOM is 144 seconds
MOTOR START DEVICE
Single Phase (-A) model compressor circuits are
equipped with a 25 ohm PTCR (Positive Temperature
Coefficient Resistor) motor starting device as standard
equipment.
The PTCR is wired in parallel with the run capacitor.
When voltage is applied, and device is cool, its low
resistance permits a large current to flow in the
auxiliary windings—increasing the motor's available
starting torque. The device then rapidly heats up and
the current levels drop to a few milliamperes. The
PTCR then becomes self-regulating, passing just
enough current to maintain its temperature to remain
in the high resistance state. Once the voltage source is
removed, the device cools down, the resistance drops
and is then ready for the next compressor start cycle.
PRESSURE SERVICE PORTS
High and low pressure service ports are installed on
all units so that the system operating pressures can
be observed. Pressure tables can be found on page
18 covering all models. It is imperative to match the
correct pressure table to the unit by model number.
Be careful to observe whether unit is operating in high
cool or low cool when utilizing the charts.
CRANKCASE HEATERS
All units covered in this manual are provided with
compressor crankcase heat.
This crankcase heater is a band type heater located
around the bottom of the compressor. This heater is
controlled by the crankcase heater relay. The heater
is only energized when the compressor is not running.
Crankcase heat is essential to prevent liquid
refrigerant from migrating to the compressor,
preventing oil pump out on compressor start up
and possible bearing or scroll vane failure due to
compressing a liquid.
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