THERMOSTAT
A cross ambient thermostat is used to maintain the desired comfort level. The thermostat reacts only to a change in temperature at the bulb location. Important to the successful operation of the unit is the position of the sensing bulb in relation to the evaporator (see Figure 8).
FIGURE 8
SENSING
BULB LOCATION
RANGE: Thermostat
(Part No.
60° F ( ± 2° ) to 90° F( ± 4° )
TEST
Remove the wires from the thermostat. Turn the thermostat to its coldest position. Check to see if there is continuity between the two terminals. Turn the thermostat to its warmest position. Check continuity to see if the thermostat contacts open.
Note: The temperature must be within the range listed to check the thermostat. Refer to the troubleshooting section in this manual for additional information on thermostat testing.
LOW AMBIENT BYPASS VALVE (Figure 9)
The HazardGard unit is designed to operate at low outside ambient temperatures. This is accomplished by the use of a bypass valve installed in the refrigeration circuit. The valve is connected between the discharge line at the compressor and the suction process tube. The valve responds to suction pressure which, when reduced in the system, causes the valve to open and bypass hot gas from the high pressure side to the low pressure side of the system. The hot gas entering the compressor mixes with the cool gas returned through the suction line, thus increasing the suction pressure. The valve is preset to open when the suction pressure reaches 50 psig. This pressure setting cannot be altered. The system can be operated at outdoor temperatures as low as 45° F before the evaporator coil will begin to accumulate frost.
To determine if the valve operates, block the return air to the evaporator coil. Turn on the unit and touch the tube at the bypass valve outlet which connects to the suction process tube. When the low side pressure reaches approximately 50 psig, the valve will begin to open and the tube will get hot. This method will determine if the valve is responding to the suction pressure change.
FIGURE 9
LOW AMBIENT
Bypass VALVE
SEALED REFRIGERATION SYSTEM REPAIRS
Equipment Required:
1.Voltmeter
2.Ammeter
3.Ohmmeter
4.E.P.A Approved Refrigerant Recovery System
5.Vacuum Pump (capable of 200 microns or less vacuum).
6.Acetylene Welder
7.Electronic Halogen Leak Detector (G.E. Type
8.Accurate refrigerant charge measuring device such as:
a.Balance Scales - 1/2 oz. accuracy
b.Charging Board - 1/2 oz. accuracy
9.High Pressure Gauge -
10.Low Pressure Gauge - (30" - 150 lbs.)
11.Vacuum Gauge -
Equipment Must Be Capable of:
1.Recovering CFC’s as low as 5%.
2.Evacuation from both the high side and low side of the system simultaneously.
3.Introducing refrigerant charge into the high side of the system.
4.Accurately weighing the refrigerant charge actually intro- duced into the system.
5.Facilities for flowing nitrogen through the refrigeration tubing during all brazing processes.
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