Manual 2100-526H
Page
15 of 24
SERVICE HINTS
1. Maintain clean air filters at all times. Also, do
not close off or block supply and return air
registers. This reduces air flow 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.
Frequency of coil cleaning will depend on duty
cycle of equipment, type of use and installation
site variables. Telecommunication type
installations in high traffic areas or in areas none
too frequent to airborne debris, will require more
frequent coil maintenance than those in areas not
subject to those conditions.
SEQUENCE OF OPERATION
NON-ECONOMIZER
Stage 1 (Y1) cooling call activates Step 1 (partial
capacity, 66%) of compressor capacity.
Stage 2 (Y2) cooling call activates Step 2 (full capacity,
100%) of compressor capacity.
WITH ECONOMIZER
Stage 1 (Y1) cooling call goes to economizer controls
for decision:
- If Enthalpy Control decides outdoor conditions
are suitable for free cooling, the economizer will
operate.
• If Stage 2 cooling call is issued during
economizer operation, the economizer will
close and the compressor will go straight to
Step 2 full capacity operation.
- If Enthalpy Control decides outdoor conditions
are not suitable for free cooling, the economizer
will not operate (or close) and Step 1 of the
compressor will operate.
• If Stage 2 cooling call is issued, the
compressor will shift to Step 2 full cooling
capacity operation.
COMPRESSOR CONTROL MODULE
The compressor control module is standard on the
models covered by this manual. The compressor
control is an anti-short cycle/lockout timer with high
and low pressure switch monitoring and alarm relay
output.
A
djustable Delay On Make And Break Timer
On initial power up or anytime power is interrupted to
the unit, the
delay on make
period begins, which will
be 2 minutes plus 10% of the
delay on break
setting.
When the delay on make is complete and the high
pressure and low pressure switches are closed, the
compressor contactor is energized. Upon shutdown the
delay or break timer starts and prevents restart until the
delay on break and delay on make periods have 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
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.
Optional Low Ambient Control
An optional low ambient control is available for both
factory and field installed options. The low ambient
control is to be applied to the WA3S/WA4S/WA5S
models when operation below 50°outdoor conditions
are anticipated. Without this device, the evaporating
pressure would fall off, and the indoor coil would ice
over.
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
insures an evaporating temperature that is slightly
above the point of ice formation on the evaporator.
