Manual 2100-695
Page
26 of 54
Second Stage Drop Out
If the liquid pressure reaches 620 PSI, the second
stage of cooling will be disabled for the remainder
of the current cooling call. This reduces the risk of
tripping the high pressure switch, while still allowing
cooling.
Low Ambient Control
At low ambient outdoor air temperatures, the fan motor
will cycle as a means of controlling the system's head
pressure to protect the system from evaporator coil freeze
conditions. The process for this system is as follows: If
the liquid pressure falls below 275 PSI, the condenser
fan will turn off. The fan will remain off while the
compressor remains running, allowing the head pressure
to build up. Once the liquid pressure reaches 350 PSI,
the fan will then turn back on at the appropriate speed.
At lower ambient outdoor temperatures, this may cycle
regularly as normal operation. In some cases, in higher
wind prone areas, the condenser fan may stay off for
prolonged durations due to low liquid pressures.
Compressor
Compressor Components
Compressor
Three Phase Scroll Compressor Start Up Information
Scroll compressors, like several other types of
compressors, will only compress in one rotational
direction. Direction of rotation is not an issue with
single phase compressors since they will always start
and run in the proper direction.
However, three phase compressors will rotate in either
direction depending upon phasing of the power.
Since there is a 50-50 chance of connecting power
in such a way as to cause rotation in the reverse
direction, verification of proper rotation must be made.
Verification of proper rotation direction is made by
observing that suction pressure drops and discharge
pressure rises when the compressor is energized.
Reverse rotation also results in an elevated sound level
over that with correct rotation, as well as substantially
reduced current draw compared to tabulated values.
Verification of
proper rotation
must be made at the time
the equipment is put into service. If improper rotation
is corrected at this time, there will be no negative
impact on the durability of the compressor. However,
reverse operation for over 1 hour may have a negative
impact on the bearing due to oil pump out.
NOTE:
If compressor is allowed to run in reverse
rotation for an extended period of time, the
compressor’s internal protector will trip.
All three phase compressors are wired identically
internally. As a result, once the correct phasing is
determined for a specific system or installation,
connecting properly phased power leads to the same
Fusite terminal should maintain proper rotation direction.
The direction of rotation of the compressor may be
changed by reversing any two line connections to the
wall-mount unit.
Compressor Control Module (CCM)
Delay-on-Make Timer
Short Cycle Protection/Delay-on-Break
Test Mode
High Pressure Detection
Brownout Protection with Adjustment
The LPC terminals are jumpered in this application.
Instead, the low pressure transducer is used for low
pressure monitoring.
Delay-on-Make Timer
In the event of power loss, a delay-on-make timer is
included to be able to delay startup of the compressor.
This is desired when more than one unit is on a
structure so that all of the units do not start at the
same time which could happen after a power loss or
building shutdown. The delay-on-make time period is
2 minutes plus 10% of the delay-on-break time period.
To ensure that all of the units do not start at the same
time, adjust the delay-on-break timer on each unit to a
slightly different delay time.
Short Cycle Protection/Delay-on-Break
An anti-short cycle timer is included to prevent short
cycling the compressor. This is adjustable from 30
seconds to 5 minutes via the adjustment knob (see Figure
43). Once a compressor call is lost, the time period must
expire before a new call will be initiated.
10% of this time is also considered on the delay-on-
make timer (see above).
High Pressure Detection
High pressure switch monitoring allows for a lockout
condition in a situation where the switch is open. If the
high pressure switch opens, the CCM will de-energize
the compressor. If the switch closes, it will then restart
the compressor after the delay-on-break setting has
expired on the device. If the switch trips again during
the same Y call, the compressor will be de-energized.
The ALR terminal will be energized signaling the unit
control board that a high pressure event has occurred
(see
Refrigerant High Pressure Alarm
on page 28).
Test Mode
By rapidly rotating the potentiometer (POT) clockwise
(see Figure 43), all timing functions will be removed
for testing.
The conditions needed for the unit to enter test mode
are as follows: POT must start at a time less than or
equal to the 40 second mark. The POT must then be
rapidly rotated to a position greater than or equal to
the 280 second mark in less than ¼ second. Normal
operation will resume after power on reset or after the
unit has been in test mode for at least 5 minutes.
