Timberline Blog

Why Compressor Safety Switches Are Essential in HVAC Systems

May 25, 2022 by Timberline

It goes without saying that the HVAC system in your home or business is complex. Of course, you don’t need to know all the details about how it functions to enjoy the benefits of properly cooled or heated air. But many of our customers enjoy learning a little bit about the different components of the system and their functions.

air conditioning unit on the roof of building

They find the information interesting and like that gaining some insight makes them a more well-informed consumer of HVAC services. With that in mind, this blog addresses a specific type of component in your air conditioning system: Compressor safety switches.

What’s the Purpose of a Compressor Safety Switch?

Compressor safety switches are also called pressure switches. Seeing “safety” and “pressure” in the previous sentence gives you a clue about their purpose.

As refrigerant travels through the refrigeration cycle, pressures and temperatures vary drastically at different points. For every point, there are normal, safe pressures and temperatures. Checking them is a way to measure and evaluate the charge or condition of your system.

For instance, on the low end of the temperature/pressure spectrum—the so-called “suction line,” where refrigerant has captured heat at the indoor coil and brought it back to the compressor—you’ll find the low-side pressure tap, usually with a low-pressure safety switch.

This switch monitors the refrigerant pressure coming back to the compressor. If it drops too low (for example, due to a frozen coil resulting from a low system charge or lack of airflow that causes the system to capture too much heat at once), the switch disengages the compressor to ensure the system doesn’t bring liquid (rather than gas) refrigerant back to the compressor and damage it.

On the other side of the compressor (the discharge line), you’ll typically find a high-pressure safety switch. Picture a scenario where the outdoor coil is plugged with material from a cottonwood tree (a common occurrence in some areas of Colorado) or other debris. That can lead to the system being unable to reject the heat to the atmosphere.

If that occurs, the discharge pressure increases and the high-pressure safety switch may kick in to ensure the compressor doesn’t start working too hard. (Cars get similar protection from what’s called a revolution limiter.)

Another instance where the high-pressure safety switch might activate is one where your air conditioner is off all day and the temperature at your home or business increases significantly, to 85-90+ degrees. The “load” or amount of captured heat coming back to the compressor can lead to higher return pressures. When the compressor is in operation, it compresses refrigerant, therefore compounding the pressure at the discharge of the compressor. When the switch shuts down the process, it protects the unit’s components.

In short, safety switches are designed to “trip” if the pressure exceeds what technicians call the “cut-in” and “cut-out” pressures—in a similar manner to the circuit breakers in your business or home’s electrical system. That means you’ll need assistance from an HVAC technician. But the affordable cost of a service call beats the alternative of an expensive system repair.

What Conditions Can Cause a Compressor Safety Switch to Trip?

Compressor safety switches are vital to the operation of your HVAC system, as any of several conditions that could otherwise damage system components can trip them, including:

  • Clogged filter or plugged coil as a result of operating your system without a filter for an extended time.
  • Collapsed duct or too many closed registers/vents
  • Dust or “cotton”-covered outdoor coils
  • Excessively low blower speed due to incorrect settings or a loose belt (where equipped)
  • Broken blower motor or belt (if equipped)
  • Weakened or out-of-calibration safety switches due to excessive operation over their lifetime

If your HVAC system stops abruptly or won’t start when you expect it to, you should call Timberline Mechanical. We can help you diagnose the problem and recommend an intelligent solution.

How Do I Know if a Compressor Safety Switch Is Functioning Correctly?

Typically, our focus is on not overworking a safety switch. However, if our technician suspects that a safety switch is faulty, we can test all the switches on your air conditioning or refrigeration system to ensure they are operating correctly.

We can do this by manipulating conditions to safely and effectively create scenarios where the safety switch interrupts the operation of the component it’s protecting, like the compressor. Some safety switches have “auto-reset” capability, meaning they’ll return the system to normal operation once pressures and temperatures stabilize. Others are “manual-reset” switches, meaning the user must manually re-engage the safety switch to ensure normal operation.

When we discover that safety switches aren’t operating properly, we replace them immediately.

Staying Ahead of Failing Compressor Safety Switches

Having our skilled technicians regularly inspect and service your HVAC system helps ensure that it’s working optimally. Regular assessments also keep you from getting caught off guard by the types of preventable system failures that compressor safety switches initiate to protect your system.

Contact us at your convenience to learn more.

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