17-08-2012, 03:43 PM
Air-Conditioning Control Systems
Air-Conditioning.ppt (Size: 656.5 KB / Downloads: 160)
Understand the electrical circuitry of a residential condensing unit
Make all electrical connections to install a condensing unit in a residential application
Troubleshoot a residential condensing unit
Understand the basic control systems used in residential air-conditioning control systems
Understand the control systems used in light commercial air-cooled and water-cooled packaged units
Make all electrical connections for a complete residential installation
Understand the control systems used In gas heat electric air-conditioning packaged units
Troubleshoot residential air conditioning system
Key Terms
Air-Cooled Package Unit
Condensing Unit
Factory-Installed Wiring
Field Wiring
Gas Pack
Indoor Fan Relay Package
Internal Pressure Relief Valve
Packaged Air-Conditioning Unit
Short-cycling
Water-Cooled Packaged Unit
Basic Condensing Units
A condensing unit is the portion of a split air-conditioning system that is mounted outside and contains the compressor, the condenser, the condenser fan motor, and the necessary devices to control these components.
A split system is one that is divided into two parts, usually a condensing unit (outside) with a fan coil unit (inside).
In most cases, the condensing unit is used with some type of equipment that will produce the air flow, and a coil must be mounted in the air flow.
Most condensing units used in the industry today are air-cooled condensing units.
Condensing Unit Components for a Simple Control System
Most modem condensing units pick up their 24-volt power supply to operate the control system from the furnace transformer or from an indoor fan relay package.
The evaporator fan motor usually is controlled by a relay when the system contains a furnace or fan coil unit and the condensing unit.
The compressor and condenser fan motor in a condensing unit are usually controlled by a contactor.
The simplest control system used on condensing units today is a contactor that controls the operation of the entire condensing unit with the exception of the internal overloads in the compressor and condenser fan motor.
Most condensing units without a high-pressure switch will have an internal pressure relief valve in the compressor that opens if the discharge pressure exceeds an unsafe level.
Condensing Unit Components for Complex Control Systems
The more complex systems incorporate a high-pressure and a low-pressure switch.
If any of the safety controls open, the compressor and condenser fan motor stop.
Several manufacturers also use a device that protects the system from short-cycling.
This device maintains a certain period of time between the cycles of the equipment so the system does not cut on and off in rapid succession (short-cycling).
This control system adds a relay and a time clock mechanism for this purpose.
Wiring
All condensing units come from the manufacturers with a wiring diagram and, in some cases, with an installation wiring diagram.
Usually it is not difficult to follow the installation instructions and wire the condensing unit correctly.