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 TM 55-1905-219-14-8
4-28.
AIR CONDITIONING SYSTEM-MAINTENANCE INSTRUCTIONS (Continued).
(18) King Solenoid Valve.
The king solenoid valve is a solenoid valve located in the main liquid line leaving the receiver. The king
solenoid valve is energized from the compressor motor controller to remain open when the compressor is
operating normally under control of the low pressure control switch. The valve is de-energized and will close
when the compressor is stopped by any other device, i.e., high pressure control switch, low voltage or overload
relay, oil pressure failure switch, stop button or other safety device. The function of the king solenoid valve is
to prevent excessive flooding of the low pressure side of the system with consequent danger of liquid
refrigerant return to the compressor upon restarting.
(19) Temperature Control Switches (Thermostats).
(a)
Operating thermostat.
The operating thermostat has a temperature sensing bulb in the space or medium being cooled
and is electrically connected to the solenoid valve. The thermostat controls the flow of liquid refrigerant to the
evaporator by opening or closing the solenoid valve. The thermostat closes and completes the electrical circuit
to the solenoid valve, thus energizing and opening the valve, when the space or other medium being cooled
rises above the desired temperature (thermostat cut-in setting). When the desired temperature is obtained
(thermostat cut-out setting), the thermostat opens, de-energizing and closing the solenoid valve.
(b)
Safety or low limit thermostat.
When there is danger of freezing the medium being cooled, such as the case of water in a chiller,
a safety or low limit thermostat is employed. The low limit thermostat is a safety device which has a
temperature sensing bulb in the medium being cooled and is wired to the compressor motor controller. The
thermostat stops the compressor when the medium being cooled drops to a dangerously low temperature
(thermostat cut-out setting). When the temperature of the medium being cooled rises to a safe level
(thermostat cut-in setting), the compressor may be restarted by pressing the motor controller START button.
(c)
The temperature control switch is wired to the cooling coil solenoid valve and functions as an
operating thermostat. The switch bulb is located in the return air stream to the cooling coil. Automatic control
sequence is described in paragraph 4-28a(22). Recommended settings and other data are tabulated below.
4-819
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