Carrier 30HH - Manual (Page 41)

Carrier
INSTALLATION
30HH,HJ
is the farthest to the right. The 30HH015 and
30HJ015 units are provided with two unloading
devices on its single compressor. Each unload­
ing device is the cylinder head bypass type and
unloads
two cylinders when the operating so­
lenoid is energized. Cylinder unloaders are en­
ergized
and de-energized by the cam operated
load switches in the step controller.
Chilled Water Temperature Controller - The
chilled
water temperature controller supplied
with each 30HH,HJ unit is the modulating re­
mote bulb type with set point and throttling range
adjustments.
The remote bulb, field-inserted in
the chilled water line, relays the chilled water
temperature
signal to the temperature controller
potentiometer which actuates the step controller.
To use the factory cam settings on the step con­
troller, the remote bulb of the temperature con­
troller
must be inserted in the return chilled
water line.
Control Bulb Location - It is generally required
with all liquid chilling package applications that
the
leaving chilled water temperature be con­
trolled. On liquid chilling packages where capac­
ity can be controlled by a throttling device, the
leaving
chilled water temperature is usually
controlled by placing the temperature control
bulb in the leaving chilled water line. However,
with
any reciprocating liquid chilling package,
where capacity is controlled by cylinder unload­
ing
or stopping and starting compressors, the
reliability and accuracy of control of the leaving
chilled
water temperature are inherently better
with the control bulb located in the return (en­
tering) chilled water line. For this reason, the
factory settings of the step controller cams on
all 30HH,HJ units are based on control from the
return
(entering) chilled water temperature. If
the unit is to be applied with the control bulb in
the leaving chilled water line, the cams must be
reset in the field. If this is required, contact
the local Minneapolis-Honeywell representative.
The use of return chilled water control and fac­
tory cam settings on the step controller apply
to
systems designed for constant chilled water
gpm thru the cooler.
SEQUENCE OF OPERATION
The sequence of control operation of the 30HH,HJ
packages may be followed by referring to the
control circuit diagram on the following page.
With power to the control circuit and the "OFF-
ON” switch in the "OFF" position, the com­
pressor
crankcase heaters are energized. When
the "OFF-ON" switch is put in the "ON" posi­
tion, the panel light goes on and, with the chilled
water
safety thermostat and the field-supplied
auxiliary interlocks satisfied, the low voltage
transformer is energized. The recycle relay
energizes the camshaft drive motor thru the
balancing relay so that the camshaft is recycled
to the no load position. When the unload direc­
tion
limit is reached, the recycle relay puts
power to the cam operated load switches and the
temperature controller takes control. By recy­
cling the controls at start-up or after a power
interruption, staggered starting of multiple com­
pressors is insured.
With the temperature controller in control the
position of the camshaft is regulated according
to the chilled water temperature. The cam oper­
ated
load switches start or stop compressors
and alternately load and unload cylinders of one
compressor to control the capacity of the unit
and balance it with the required load. During
operation a change in temperature causes an un­
balance in the temperature bridge circuit. This
causes the balancing relay to energize the cam­
shaft drive motor winding which turns the cam­
shaft to increase or decrease the unit capacity
as required.
All 30HH and HJ units are designed with Liquid
Line Solenoid Drop. The liquid line solenoid in
each refrigerant circuit is in parallel with the
holding coil for the compressor in that circuit.
The solenoid is energized when the compressor
starts and the liquid line valve opens. When the
compressor
stops, the solenoid is de-energized
and the valve closes. Where a refrigerant circuit
has more than one compressor, the liquid line
valve
opens when the first compressor starts
and closes when the last compressor stops.
The complete unit is stopped if the "OFF-ON"
switch is put in the "OFF" position; if the chilled
water safety thermostat contacts open; or if the
contacts
of any auxiliary interlock open. Indi­
vidual compressors are stopped if the motor
winding high temperature cutout contacts open
or if the high or low pressure switch of the re­
frigerant circuit cuts out.
The compressor crankcase heater is turned on
when the compressor is cycled off to prevent
dilution and crankcase refrigerant condensation.
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