Installation, Operation and Maintenance Manual
VariCool
®
VAV
20
Subject to change without notice.
10.20-IM (0818)
CAUTION
Confirm that any coil cleaning agents,
detergents or solutions are suitable for
use on a copper tube/aluminum fin coil. If
the cleaning agent is to acidic or alkaline,
damage to the coil fins may result.
Rinse all coils thoroughly after any coil cleaning
Use a suitable fin comb after the coil cleaning to straighten
any bent fins.
Water Side Economizer Coil
If a unit contains the optional water side economizer coil it
may also require a periodic cleaning These coils will need
to be cleaned using a chemical solution These are available
commercially Follow all manufacturer recommendations
and safety warnings
Water Valves
At least once a quarter check the water vales to make sure
that no leaks are present Look at the valve stem and all
piping joints
If any leaks are found follow the manufacturers
recommendations for tightening any seals or replacing any
gaskets
Hard Start Kit
A start assist device is utilized on all single phase units The
purpose of this device is to assist the compressor in starting
under low voltage conditions
A capacitor in conjunction with a Positive Temperature
Coefficient (PTC) relay is installed across the run and
start windings of the motor The PTC device utilizes a
ceramic element with a predictable thermal response to
the introduction of electric current When the compressor is
called upon to start, the start capacitor provides a voltage
boost to the start winding of the motor and causes the motor
to turn As the starting current is introduced across the start
windings, the PTC element begins to warm When the PTC
device reaches approximately 250° F (corresponding to 06
- 08 seconds), the resistance in the element increases and
creates an open switch that releases the start winding from
the circuit and the motor continues to run If the compressor
does not start before the device heats to 250° F, it will not
start until the PTC device cycles through a cool-down period
(usually 2 - 3 minutes) A compressor off-cycle timer is
included in the electrical circuit for this purpose
The time delay also helps the refrigerant system pressures
to equalize at the end of the run cycle This helps the
compressor during the starting process in that it is not
attempting to start against a high discharge pressure
INFORMATION
Verify that this timer is set for 3 or more
minutes
Checking Hot Gas Bypass Valve
1�
Connect a calibrated thermocouple lead to the outlet
line at the hot gas bypass valve Tie wrap and insulate
the lead
2�
Connect a low pressure refrigerant gauge to the suction
line
3�
Connect a high pressure refrigerant gauge to the liquid
line
4�
Operate the air conditioner in the cooling mode until the
system is stabilized (Approximately 15 minutes)
5�
If the high side pressure is not at or above 400 psig,
block off the condenser inlet air stream until the
pressure is above this threshold This will simulate
system performance level close to the design condition
of 95° F ambient
6�
The hot gas bypass valve setting is 104 psig
A�
If the suction pressure is 104 psig the
thermocouple reading should be approximately
117° F or higher Please note that it may be
necessary to block off some of the evaporator air in
order to check this condition
B�
If the suction pressure is above 104 psig the
thermocouple reading should be less than 117° F
C�
If the suction pressure is below 104 psig the hot
gas bypass valve should be adjusted to raise the
pressure
Adjustment Of Hot Gas Bypass Valve
The function of the hot gas bypass valve is to prevent the
suction pressure from falling below a predetermined set
point, thereby balancing the system The set point is typically
104 psig (R-410a)
1�
Connect a low pressure refrigerant gauge to the suction
line
2�
Operate the air conditioner in the cooling mode until
system is stabilized (Approximately 15 minutes)
3�
Remove the seal cap that covers the adjustment screw
of the hot gas bypass valve
4�
Adjust the valve by turning the stem A CLOCKWISE
turn will increase the pressure setting A
COUNTERCLOCKWISE turn will decrease the
pressure setting One complete turn is equal to
approximately 4 psi change
Summary of Contents for VariCool VAV
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