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operation
8.0 OPERATION
8.1 PRE-START UP
After the installation is completed, a review of the following items
should be preformed before the system is placed into operation:
A. Check electrical connections, fan bushing set screws, motor
mount bolts, coil flange bolts, drain pan flange bolts, and
all other fasteners for tightness. If required, be sure the
thermostatic expansion valve bulb is properly located, strapped,
and insulated.
B. For systems with a defrost time clock check the timer to see
that it is set for the correct time of day and the starting pins
have been installed (normally two or three sets per day).
Defrost should be scheduled when the freezer doors are not
likely to be open.
C. When the unit is first started the room temperature is typically
above the contact closing temperature of the fan delay
thermostat, if a fan delay thermostat is provided for Electric
Defrost units (see that particular units electrical diagram). The
fans may remain off for a lengthy period of time. To prevent
this delay it is permissible to install a temporary jumper wire
between terminals “1R” and “2B”. Once the room temperature
is below 25°F the jumper wire should be removed.
D. The motors for STC units are greased from the motor
manufacturer.
8.2 OPERATION CHECKOUT
With the system operating, check the supply voltage. The voltage
must be /- 10% of the voltage marked on the unit nameplate
and the phase to phase unbalance should be 2% or less.
LISTEN CAREFULLY to the unit to make sure there are no unusual
sounds. Sounds such as a noisy motor, the fan(s) scraping on the
housing, or loose fasteners allowing parts to rattle need to be
addressed immediately before continued unit operation.
Check the room THERMOSTAT setting. Be sure it functions properly.
For RECIRCULATED refrigeration systems the hand expansion
valve should be opened slowly until either condensate or frost
forms on the return bends from the bottom to the top of the coil.
A good indicator is when the defrost relief valve reads 5 PSI above
suction pressure.
For FLOODED refrigeration systems check to make sure the float
valve is working properly and allows refrigerant into the drum to
the appropriate level when the level is sufficiently low. If a hand
expansion valve has been added, the valve should be set to allow
liquid make up 70% of the time.
For DIRECT EXPANSION systems let the system balance out
at the desired room temperature and check the operation of
the expansion valve by properly measuring the superheat at the
sensing bulb. As much as thirty minutes may be required for the
new balance to take place after an adjustment is made.
For BRINE or WATER COOLING systems keep the closest vent
to the coil open while the fluid fills the coil to allow trapped air to
escape. Close the vent valve once fluid flows out of the valve and
check for water hammer in the coil.
With HOT GAS DEFROST systems allow the coil to frost, then
manually advance the defrost timer to initiate a defrost cycle.
Observe the defrost cycle to see if all controls are functioning
properly and that the coil is clear of all frost before the system
returns to refrigeration. Adjust the time clock pins if necessary.
Reset the defrost timer to the correct time of day. A defrost cycle
is only needed when the frost build up is such that it impedes
the airflow through the coil. The defrost requirements will vary on
each installation and may change depending on the time of the
year and other conditions..
With ELECTRIC DEFROST systems allow the coil to frost then
manually advance the defrost timer to initiate a defrost cycle.
Observe the defrost cycle to see if all controls are functioning
properly and that the coil is clear of all frost before the system
returns to refrigeration. Adjust the time clock pins if necessary.
Reset the defrost timer to the correct time of day. A defrost cycle
is only needed when the frost build up is such that it impedes
the airflow through the coil. The defrost requirements will vary on
each installation and may change depending on the time of the
year and other conditions.
