Environmental control unit for harsh conditions

Abstract

A method of controlling an air conditioning system of the type having a variable capacity compressor circulating refrigerant through a condenser, an expander, an evaporator and returning to the compressor. Sensors are disposed to sense a refrigerant condition selected from one of pressure and temperature on one or both the compressor high pressure and low pressure side; and, in the event of an overload condition, the sensors generate a control signal that effects operation of an actuator for moving a member in the compressor to vary the compressor capacity to the lowest capacity output. Alternatively, the generated control signal may vary the compressor speed.

1 . An environmental control unit comprising:
 a variable output compressor;   an outdoor coil connected to said variable output compressor via a first conduit;   an indoor coil connected to said variable output compressor via a second conduit; and,   a controller for said variable output compressor compressor, said controller comprising:
 a first sensor connected to said first conduit for sensing a compressor high side condition and generating a first signal; and, 
 a control circuit for generating a control signal in response to said first signal in order to reduce a capacity of said variable output compressor, wherein said control circuit includes one of a fixed resistor with a shunt switch and a thermistor responsive to the first signal. 
   
     
     
         2 . The unit of  claim 1 , further comprising:
 a second sensor connected to said second conduit for sensing a compressor low side condition and generating a second signal;   wherein said control circuit generates a control signal in response to said second signal and includes a fixed resistor with a shunt switch responsive to said second signal.   
     
     
         3 . The unit of  claim 1 , wherein said first and second sensors comprise one of a pressure sensor and a temperature sensor. 
     
     
         4 . The unit of  claim 1 , wherein said first and second sensors are positioned in series. 
     
     
         5 . The control unit defined in  claim 1 , wherein the control circuit includes a first thermistor and a second thermistor. 
     
     
         6 . An environmental control unit comprising:
 (a) a variable output compressor;   (b) an outdoor coil connected to said variable output compressor via a first conduit;   (c) an indoor coil connected to the variable compressor via a second conduit;   (d) a controller for the variable output compressor, the controller including:
 a first sensor connected to said first conduit for sensing a compressor high side condition and generating a first condition signal, 
 a control circuit operative for generating a discrete control signal in response to said first condition signal in order to reduce a pumping capacity of the variable output compressor. 
   
     
     
         7 . The unit described in  claim 6  wherein the control circuit includes a fixed resistor with a shunt switch operative in response to the first condition signal. 
     
     
         8 . The control unit of  claim 6 , further comprising:
 a second sensor connected to said second conduit operative to sense a compressor low side condition and generate a second condition signal, wherein said control circuit is operative for generating a different discrete control signal in response to said second condition signal.   
     
     
         9 . The unit defined in  claim 8 , wherein said control circuit includes a fixed resistor, with a shunt switch operative in response to the second condition signal. 
     
     
         10 . The unit defined in  claim 6 , wherein the control circuit includes a thermistor operating in response to the first condition signal.