CONDENSER IOM MANUAL
19
1. Block off the intake air to the condenser with cardboard
until a constant discharge pressure can be obtained. This
will lower the possibility of overcharging (for units with
fan cycling only).
a. R407C Refrigerant- Allow the discharge pressure to
rise to 325–350 psig and hold it constant.
b. R410ARefrigerant- Allow the discharge pressure to
rise to 445–480 psig and hold it constant.
2. Slowly meter liquid refrigerant through the suction side
while watching the pressure gauges and monitoring
superheat and sub-cooling temperatures.
CAUTION
Add liquid refrigerant slowly to prevent the
refrigerant oil from washing out of the compressor.
3. Take a superheat temperature reading near the feeler
bulb from the thermostatic expansion valve with the
temperature measuring device being well insulated. The
ideal superheat temperature is 12–15 °F. Maximum
allowable superheat temperature is 20 °F.
4. While monitoring the pressure, take a sub-cooling
temperature reading on the output side of the condenser.
The sub-cooling temperature should be 10–20 °F.
5. If necessary, (slowly) add liquid refrigerant to the suction
side to achieve the sub-cooling temperature.
6. If the unit has hot gas reheat (optional), the previous steps
are still followed except the hot gas reheat valve must
be open to allow refrigerant to flow into the reheat coil
to obtain the proper amount of refrigerant charge. This
can be done by using the system controller to enable a
call for dehumidification (lower the humidity setpoint).
This process may need to be repeated several times.
After cycling the system through the hot gas reheat cycle,
recheck the system charge with the system only in the
Cooling mode.
CAUTION
Remove the blockage to the air intake of the
condenser.
7. Fill out the applicable sections of Warranty Registration
and Start-Up Checklist.
2.7.4.2 -30 °F Flooded Head Pressure Control
NOTE: For units using flooded head pressure control, a receiver
is used to store the refrigerant during the time the condenser is
not utilizing the extra refrigerant charge.
NOTE: It is important not to exceed 80% of the total
condenser and receiver volume to allow room for expansion.
The most accurate way to determine the total system
refrigerant charge is by calculating it as discussed in Section
2.7.2. This procedure will assist in charging a flooded system
to achieve proper operation during low ambient conditions.
Perform the initial system charge as described in Section
2.7.4, steps 1 – 3. Energize all solenoids, hot gas bypass, hot
gas reheat, etc. The condenser fan nearest the condenser
header should be operating continuously. If not change the
fan control setting to force continuous operation. All other
fans, if additional fans exist, should be off during this time.
The head pressure control valve setting is printed on the
valve. This setting is the lowest head pressure that will be
maintained during unit operation. Add refrigerant to the
system (slowly metering). Charge the unit until you reach the
HGBP valve setting if applicable.
Set up the HGBP valve and disable the solenoid after
adjusting. Slowly continue to meter in refrigerant until you
reach the head pressure control valve setting printed on the
valve (225 psig for R407C; 290 psig for R410A).
All other low ambient controls should not be enabled during
the final charging procedure, deenergize the solenoids to
prevent operation.
It is best to under charge the system and operate the unit in
the cooling mode to achieve this, otherwise you may add
refrigerant above the valve setting and then will be unable to
test the head pressure control valve operation.
The head pressure control valve modulates to maintain
system head pressure; you will witness this if the above
procedure is strictly followed. Under low ambient conditions
with the header fan functioning, the head pressure will lower
during operation. The valve will not allow the pressure to drive
below the printed setting on the valve.
Check the system superheat and sub-cooling temperatures.
They should be within the specifications in Section 2.7.4.1
(steps 3 and 4).
Turn the unit off for 15–30 minutes. Restart the system and
observe the operating pressures. The suction pressure
should not dip or drive below the low pressure switch
setting.
2.7.4.2.1 Checking the Charge
To ensure you are not over charged, set up the condenser
fan to maintain pressure (320 psig for R407C; 440 psig for
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