Commercial Air Conditioner
Model: heat pump, 10SEER UNITS
12
automatically when pressure value becomes normal
.
Fig.1-10
RELAYS
Relays provide control switching .The voltages controlled may be either low(24V.A.C.)or line voltage. It is
usually 24 volts. Contact voltage may be either low or line voltage.
COMPREESSOR CONTACTOR
The compressor contactor is a large relay. The coil uses 24 volts but the contacts carry line voltage .The
contactor controls compressor and the outdoor fan operation. Some contactor use single pole
contacts ,while others use 2-pole or 3-pole contacts.
Single-pole contacts break power to only one side of the compressor and outdoor fan .The other side
remains hot with voltage. The 2-pole or 3-pole contactor breaks power to all sides of the compressor and
outdoor fan.
CAUTION:WITH A SINGLE POLE CONTACTOR,ONE SIDE OF A 240 V.A.C.CIRCUIT IS ALWAYS
HOT.THIS MEANS ALL WIRING IN THE HIGH VOLTAGE CIRCUIT MAY HAVE A POTENTIAL OF 120
V.A.C.TO GROUD.BEFORE SERVICING THE UNIT ALWAYS TURN OFF POWDER AT THE UNIT
DISCONNECT SWITCH.
OPTIONAL RELAYS AND KITS
A Time-Delay in the compressor contactor low-voltage circuit allows time for system pressure to equalize
before re-starting the compressor.
This relay user solid state circuitry to measure the time since the power was interrupted. It is set for up to
3 minutes .It is not field adjustable. It is a delay on break timer.
Compressor relay PCB
Fig.5-1
START KITS(OPTIONAL)
This special relay uses the EMF generated by
the compressor start windings to take a start capacitor
out of the circuit. The relay and its companion capacitor can start the compressor at low voltages and
against higher pressure, such as those caused by non-bleed port expansion valves.
Start kits are not normally required with scroll compressors. The operating characteristics of the scroll
compressor make a start kit unnecessary.
6.APPLICATION
Before specifying any air conditioning equipment, a survey of the structure and a heat gain calculation
must be made. A heat gain calculation involves identifying all surfaces and openings that gain heat
from the surrounding air and quantifying that heat gain. It also calculates the extra heat load caused by
sunlight and by humidity removal. These factors must be considered before selecting an air conditioning
system to provide year round comfort. The Air Conditioning Contractors of America (ACCA) J Manual
method of load calculation is one recognized procedure for determining the cooling load.
