McQuay seasoncon ALP-067A, Installation And Maintenance Data

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Alarm Bell - Optional
The 24 volt alarm bell is mounted inside the control center but not
wired to the control circuit. It is expected that in most cases,
the customer will want to relocate the bell where it will be more
easily heard in the event of a safety failure. There are leads for
connection of the bell inside a junction box which is located in the
unit control center. All that is necessary is that the bell be
mounted in a preferred location and wired to the leads in the junc-
tion box.
The bell is wired into the control circuit so that it will sound
whenever there is a failure due to low oil pressure, motor overload,
or excessive condenser pressure.
Hot Gas Bypass - Optional
Hot gas bypass is a system for maintaining evaporator pressure at or
above a minimum value. The purpose for doing this is to keep the ve-
locity of the refrigerant as it passes through the evaporator high
enough for proper oil return to the compressor when cooling load con-
ditions are light.
The system usually consists of a solenoid valve piped in series with
a pressure regulating valve as shown. Units are available with op-
tional hot gas connection with a manual shutoff valve and capped stub.
A hot gas bypass kit consisting of a 115 volt solenoid valve and a
pressure regulating valve is available from McQuay under ordering
number 886-321262B-02 for ALP units 067AS/D through 159AD.
The solenoid valve should be wired to open whenever the unit t h e r m o -
stat calls for the first stage of cooling (see Figure 10). The pres-
sure regulating valve that McQuay offers is factory set to begin
opening at 58 PSIG (32F for R-22) when the air charged bulb is in
an 80F ambient temperature. The bulb can be mounted anywhere as
long as it senses a fairly constant temperature at various load con-
ditions. The compressor suction line is one such mounting location.
It is generally in the 50F to 60F range. The chart on page 50 indicates
that when the bulb is sensing 50F to 60F temperatures, the valve will
begin opening at 54 to 56 PSIG. This setting can be changed as in-
dicated above, by changing the pressure of the air charge in the
adjustable bulb. To raise the pressure setting, remove the cap on
the bulb and turn the adjustment screw clockwise. To lower the set-
ting, turn the screw counter-clockwise. Do not force the adjustment
beyond the range it is designed for as this will damage the adjust-
ment assembly.
The regulating valve opening point can be determined by slowly reduc-
ing the system load while observing the suction pressure. When the
bypass valve starts to open, the refrigerant line on the evaporator
side of the valve will begin to feel warm to the touch.
CAUTION: The hot gas line may become hot enough to cause injury in
a very short time so care should be taken during valve
checkout.
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