5- 



The operation and the interrelationships between these control 

 instruments are described in the section on Control Sequence. 



At the side of the main panel is the electric panel (fig. 4) housed in 

 a heavy metal cabinet with lock door. On this electric panel are fuse 

 blocks, a # two- speed magnetic starter for the compressor, a time clock 

 for the air-conditioning unit cycle change, relays, and an interval timer 

 for operating the refrigeration solenoid- valve controls. At the bottom 

 are two timer-delay relays to control the blowers on cycling of units, 

 two blower magnetic starters, an evaporative condenser magnetic 

 starter, and a defrost timer. On the forward end of the panel, so as to 

 be viewed from the front of the cabinet, are indicator lights that show 

 which air -handling unit is in operation, how many refrigeration circuits 

 are on, and when moisture is being introduced into the cabinet. Below 

 these lights are switches to control the cycling of the units, operation 

 of the defrost coil, and an on-off switch for the compressor. An addi- 

 tional safety switch to control the operation of the compressor is 

 mounted on the panel. Above the panel is a Modutrol motor with four 

 mercury switches to control operation of the refrigerant solenoid valves. 



Control Sequence 



One time-pattern transmitter, located on the control panel, has an 

 arm which follows the curvature of a cam shaped to give the desired 

 temperature to be maintained in the cabinet. This transmitter produces 

 an air signal ranging from 2 to 14 p.s.i. over the range of the instrument, 

 which is from -50° to +150° F. This signal is passed to the temperature 

 controller-recorder installed above it. 



If the temperature in the cabinet is below that desired, the air- 

 pressure signal is built up by the recorder and is passed through a 

 pneumatic motor to the variable transformer, which passes current to 

 the electric air heaters to bring the conditions back to the control point. 

 If the cabinet is warmer than indicated by the index on the instrument 

 dial, the transmitted -air signal decreases, and when it falls below 

 6 p.s.i. refrigeration is turned on. The temperature' can be raised or 

 lowered as much as 40° F. in 60 minutes. 



A 6:1 pneumatic relay is provided in the refrigeration- control air 

 line to transmit air to the compressor-capacity-control device. As the 

 output-air signals from the controller-recorders drop, the air pressure 

 of this pneumatic relay also drops, giving a lower pressure to the 

 capacity- control device to bring more cylinders into operation. 



Since the compressor has this control providing for four" steps of 

 capacity by cylinder loading, as well as a control for operation at two 

 speeds, and since five steps of capacity are provided by selection of 

 the refrigeration- coil areas, it may be seen that by various combinations 

 refrigeration capacity in forty steps may be obtained. 



