Why Is My Compressor Shutting Off? Temperature Sensors and Switches

July 18, 2023
VMAC air compressors  are equipped with a switch that includes an oil temperature sensor. If the compressor oil gets too hot, the switch signals the on-off controller to disengage the air compressor, which shuts down the system to prevent temperature-related damage.

If your compressor has shut down due to going over temperature, it could be for any of the following reasons:

  • Ambient temperature too high or not enough ventilation
  • Too low oil level
  • Wrong type of oil is being used
  • Dirty oil cooler
  • Thermostatic valve not working (if applicable)
  • Dirt/obstruction in oil lines
  • Plugged oil filter
  • Restricted air flow over the air-to-liquid cooler
  • Engine coolant is too hot when entering the liquid-to-liquid heat exchanger
  • Faulty temperature switch

Why Does My Air Compressor Automatically Shut Off?

Excessive oil temperatures can cause damage to your air compressor and is one of the most common causes of failure. Overheating can result in premature lubricant degradation, high oil and moisture carryover, varnishing of the compressor internals, and heat damage to other system components such as the oil filter, cooler, and separator filter. Lubricant flash points also present a fire hazard.

The costs of rectifying these issues through temperature switches and controllers can result in significant cost savings, minimized downtime, and reduced risk of injury.

Types Of Over-Temperature Controls

VMAC air compressors are designed to handle over-temperature situations in different ways, but they will all use some sort of mechanism to detect when air compressor oil is too hot and automatically shut down the system.

Some VMAC systems use the control box to monitor system temperature and automatically turn fans on and off, as needed, to regulate the temperature. For example, this type of temperature control is used in the UNDERHOOD40, H40/H60 hydraulic, and D60 diesel air compressors. Meanwhile, the G30 air compressor has a fan that runs continuously and instead uses a switch to shut down the compressor if the temperature rises too high.

On-Off Controllers

An on-off controller is the simplest form of a temperature control device. The output from this type of device is either fully on or off, with no middle state. An on-off controller will cut power or disengage the clutch when the temperature passes the set point. On-off control is usually used when precise temperature control is not necessary.

Limit Controllers

A limit controller is an on-off controller used for alarm indication. This type of controller uses a latching relay, which must be manually reset, and is used to shut down a process when a certain temperature is reached.

Temperature Sensors & Switches

Temperature sensors and switches are relatively easy to set up, making them a popular option for temperature control. Temperature switches and sensors are typically used to monitor compressor coolant, oil and air inlet temperatures, discharge air temperatures, and log the variations.

Temperature switches are slightly more complex and include a sensor plus the ability to send signals. When the temperature passes a set point, the switch sends a signal to a controller to do something to the application, like cut the power, sound an alarm, turn on a light, or disengage the clutch.

Some immersion temperature switches are appropriate for applications that require an inexpensive solution to simple temperature control. These switches activate with a specific rise in temperature. They are available with a wide range of temperature pre-set values and a set point range, set point tolerance, maximum temperature cut-out setting, and probe length.

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