27-06-2012, 01:49 PM
Heating, Ventilating, Air-Conditioning & Refrigeration Technology
Heating, Ventilating, Air-Conditioning.ppt (Size: 250 KB / Downloads: 58)
CONTROLS FOR AIR CONDITIONING
Must correctly control the indoor fan, outdoor fan, and compressor
Indoor fan must be on when the compressor is operating
Outdoor fan is often on when compressor operates
Indoor fan may operate continuously
Thermostat – Operating control
High-pressure switch – Safety control
PRIME MOVERS – COMPRESSORS AND FANS
Consume the most power
Operate at high voltage
Control circuits are usually 24 V
Electronic controls more economical than before
Controls for convenience, comfort, and efficiency
LOW-VOLTAGE CONTROLS
Low voltage provided by a transformer
Controls the operation of devices that, in turn, control the system compressor and fans
Example: When a low-voltage contactor coil is energized, contacts close, energizing the system compressor
OPERATING CONTROLS FOR OLDER AIR-COOLED SYSTEMS
Thermostat controls space temperature
Fan relay starts and stops the indoor fan
Compressor contactor starts and stops the compressor and outdoor fan
Compressor starting and running circuits
OPERATING CONTROLS FOR MODERN EQUIPMENT
Electronic programmable thermostats
Fan relays are smaller than older ones
Starting circuit
Fewer components
Run capacitor in series with the start winding
PTC-Positive temperature coefficient
SUMMARY
Air conditioning system controls cycle the compressor, condenser fan motor and indoor fan motor on and off at the proper time
Typically, the outdoor fan motor and indoor fan motor are operating whenever the compressor is in operation
The thermostat controls the operation of the major system components based on space temperature
Typical residential systems are controlled by low voltage circuits.
Newer systems use motor protection controls in the event of dirty condensers, short cycling, overcurrent conditions or low charge protection
New electronic thermostats provide more accurate temperature control
Electronic controls can protect systems from both high and low voltage conditions
Solid-state controls often have self-diagnosing features.