Hillphoenix Adaptapak ADP-M0000-L0032, Инструкция по установке и эксплуатации

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AdaptaPAK® Maintenance and Troubleshooting
The T-Stat senses the changes in temperature that cause the control to open and close through a device called
a sensing bulb. The sensing bulb is mounted so that it reacts to the evaporator inlet air. Due to the continuous
operation of the evaporator fan, the temperature of the recirculating air in the cooler is an average of the product
temperature, the wall temperature, and any infiltrated air and any other loads such as those caused by a person
entering the cooler. When the air temperature reaches the cut-in point of the control it calls for refrigeration.
In most medium temperature applications, the on-cycle set point at which the system calls for refrigeration is
40 ºF. This set point is usually referred to as the cut-in point. In most medium temperature applications, the system
will continue running until the lower, or cut-out, set point is reached; 37 ºF is typically used for the cut-out point. The
difference between the set points allows the compressor to cycle on and off without short cycling. Each compressor
start causes wear. Too much starting and stopping (short cycling) shortens the life of the compressor and increases
the maintenance required to keep it running. The best way to avoid short cycling is to spread the set points wide
enough apart that the system is not continuously calling for refrigeration.
The upper set point, the Cut-in, in this example is 40 ºF. Above 40 ºF, bacterial growth rates increase dramatically,
and below 40 ºF, they decline. So a basic product safety check for any system should always be that the Cut-out and
Cut-in points are properly set.
In addition to temperature controls, refrigeration systems also commonly rely on pressure control schemes.
These work in basically the same manner as the temperature differential controls except that the set points are
determined in psig instead of degrees F. To imagine how such a system would work, in the example described above,
substitute pressure in psig for temperature in ºF, and 68 psig and 64 psig, respectively, for the Cut-in and Cut-out
points (on R-22 systems).
Low Pressure Control
A device called a Low Pressure Control (LPC) monitors the pressure in the system.
Besides controlling the set points in the system, pressure controls also almost always work as safety controls. In
some systems, both T-Stats and LPCs are used.
In these cases, the LPCs protect the system from a loss of refrigerant charge by being set to cut-out at a pressure
that is lower than anticipated low-side operating pressure.
Any time the compressor operates with an undercharge, the windings on the motor are apt to overheat and
significant damage can then occur. As long as the system operates above the minimum pressure, the LPC remains
in what is called the normally closed (NC) position. Small leaks that cause a gradual loss of refrigerant, and
minute drops in pressure, initially trip the LPC to the open position which briefly stops the compressor. As the leak
increases, the LPC trips more and more frequently until it eventually gets to the point where the system only runs for
a few seconds before cutting out. At that point the high and low side pressures will equalize and the system will try
starting once again. This again results in short cycling. As already noted, short cycling is not good, but destroying the
compressor by operating indefinitely with an undercharge is worse.