The low-pressure control switch is critical for many commercial refrigeration systems, including walk-in coolers and freezers. This switch usually contains two separate settings adjustable by an HVAC technician. The first setting determines the system pressure that allows the compressor to cut in, and the other setting determines when the system should shut down for a low-pressure condition.
An undercharged system can result in compressor damage just as easily as an overcharged system, so it's essential for the low-pressure cut-off to function correctly and accurately. Understanding how this safety device works and how it can affect your refrigerator may help you avoid more substantial forms of damage.
What Are the Dangers of Low Pressure?
Refrigeration systems share many qualities in common with air conditioning systems. Like air conditioning systems, they rely heavily on maintaining correct refrigerant pressure levels throughout the system. When operating normally, the evaporator coils will contain a saturated mix of vapor and liquid that turn wholly to vapor before reaching the compressor.
If refrigerant pressure falls too low, the temperature in the evaporator can drop. This condition leads to freezing on the coils and may prevent the refrigerant from cycling into a vapor. Liquid refrigerant can then reach the compressor, a situation commonly known as "slugging." Slugging will rapidly overheat, wear out, and even destroy the compressor or compressors in your system.
Note that pressure follows temperature, so some systems use the low-pressure control switch to set temperature and protect the compressor. Using the control in this way requires care and knowledge of the refrigerant in this system, so you should leave any adjustments to an expert.
What Causes Your Low-Pressure Control to Trigger?
Many low-pressure controls include an automatic reset feature. As a result, a triggered low-pressure control may result in short-cycling behavior. Your refrigeration unit will run until the pressure drops below the cut-off, at which point the system will shut down until pressure returns to the appropriate level. Obstructions or contamination in the refrigerant lines can cause these problems.
The low-pressure control can also trigger due to refrigerant leaks or an undercharge. Without enough refrigerant in the system, the pressure control will shut down the system to prevent damage to the compressor. If your refrigerant charge is low enough, the system may not start at all since the refrigerant pressure will never reach the cut-in setpoint.
However, it's crucial never to condemn any single component if you experience a low-pressure shutoff. Instead, allow an HVAC technician to perform a thorough diagnosis on your refrigeration system. In many cases, the problem may not be what you expect, and a complete inspection will allow a technician from a place like North Texas Climate Control to find the actual cause for the most cost-effective repair.