An inline switch such as this may be used to monitor line pressure. Should the system pressure drop below some point where there is insufficient refrigerant for safe operation of the compressor, this switch will signal the A/C controller to shut down compressor operation to avoid compressor damage. On occasion, these switches can fail and prevent the compressor from turning on, even though the system is adequately charged. The system has to be purged and recharged for switch replacement. However, you can jumper a failed switch so it is ignored. This will allow you to continue to operate the A/C system, but you won’t have the safety of the low-pressure switch to protect the compressor should you have a refrigerant leak.