Troubleshooting Defective Pressure Switches in Air Conditioners

By Fix4U Team
Air Conditioners, Appliances

Air conditioning systems rely on pressure switches to monitor and control the flow of refrigerant. If these switches malfunction, it can lead to a variety of problems – from reduced cooling capacity to complete AC failure.

Pressure switches act as a safety mechanism to cycle the compressor on and off based on internal refrigerant pressures. When they fail, refrigerant pressures can rise to dangerous levels or cause components like the compressor to cycle erratically.

In this guide, we’ll cover the role of AC pressure switches, trouble signs of defective switches, and steps DIYers can take to test and replace faulty switches.

How AC Pressure Switches Work

Air conditioners have two pressure activated switches – a high pressure switch and a low pressure switch:

High Pressure Switch – This switch is located on the discharge line leading from the compressor to the condenser. It monitors for high pressure conditions that could damage the compressor or indicate blocked airflow. If refrigerant pressures get too high, it shuts off the compressor.

Low Pressure Switch – This switch sits on the suction line between the evaporator and compressor. It monitors for low refrigerant pressure and shuts off the compressor if pressure drops due to leaks or other issues.

Both switches are normally closed. They open the electrical control circuit when abnormal refrigerant pressures are detected, shutting down the compressor to prevent damage.

Signs of a Defective Pressure Switch

Fix4U Repairs' Technicians Fixing Defective Pressure Switches In Air Conditioners Problem In Gta

Some common symptoms that point to a faulty AC pressure switch include:

  • Compressor repeatedly cycles on and off
  • Compressor won’t turn on at all
  • AC blows warm air or lacks cooling power
  • Higher energy bills from short cycling
  • Frosted evaporator coils indicate low refrigerant
  • Error codes or fault lights on AC control panel

If you notice these issues, testing the pressure switches should be your next troubleshooting step.

Dangers of Faulty Pressure Switches

When pressure switches fail, they can no longer perform their vital safety function of regulating refrigerant pressures. The impacts of unchecked pressure buildup include:

  • Compressor damage – With no high pressure cut-off, discharge pressures can rise high enough to destroy compressor bearings, valves, pistons, etc.
  • Burst refrigerant lines or coils – Extreme pressures place major strain on lines and coils, which can rupture and leak refrigerant.
  • Safety hazards – Excessive pressure buildup can potentially cause explosions or releases of hazardous refrigerant gases.
  • Higher operating costs – Refrigerant pressures outside the ideal range lead to reduced efficiency and shorter equipment lifespan.

Replacing faulty switches promptly is critical to avoid catastrophic and costly AC damage.

Testing Pressure Switches

You can conduct some basic checks to determine if your AC pressure switches are functioning properly:

1. Check electrical continuity

  • Use a multimeter to check continuity between the terminals on each pressure switch when the compressor is off.
  • You should get a closed circuit reading on both low and high pressure switches. If not, the switch may be stuck open.

2. Monitor cut-in and cut-out pressures

  • Using AC gauges, observe the refrigerant pressures at which each switch opens and closes as the system runs.
  • Compare to the manufacturer’s pressure specifications. Switches operating outside the cut-in/cut-out range may be defective.

3. Watch for rapid ON/OFF cycling 

  • If the compressor turns on and off every few minutes, a faulty switch may be causing short cycling. Rapid cycling strains the system.

4. Conduct voltage tests

  • Check voltage to each pressure switch while operating to confirm 24V power is supplied. Lack of voltage indicates a wiring problem versus faulty switch.

How to Replace Pressure Switches

If testing confirms defective operation, the pressure switches will need replacement. Here are the basic steps:

  • Turn off power to AC: Locate the disconnect switch near the condenser and turn off power to the AC before starting any repairs.
  • Remove switch cover: Remove any covers or panels to access the faulty pressure switch.
  • Disconnect wiring: Label wires and disconnect the electrical connector leading to the pressure switch terminals.
  • Remove pressure switch: Use a wrench to detach the faulty pressure switch from the refrigerant line. Cap the open refrigerant line immediately to contain any refrigerant.
  • Replace pressure switch: Install the new, properly rated pressure switch on the same refrigerant line in the same orientation. Follow manufacturer torque specs.
  • Reconnect wiring: Attach wiring to the correct terminals on the new pressure switch. Ensure tight, secure connections.
  • Check for leaks: Turn on power and check switch connections for any refrigerant leaks using leak detector spray. Repair any leaks before operating AC.
  • Verify operation: Run the AC system and use gauges to confirm the new switch is cycling on/off at the correct refrigerant pressures.

When to Call a Professional

DIYers comfortable working with electrical, refrigerant systems, and AC diagnostics can replace pressure switches on their own. However, if any of below are true, contact a licensed HVAC technician for pressure switch replacement:

  • You are unsure how to safely recover refrigerant from the AC system
  • The AC unit uses R-410A refrigerant which requires special handling
  • The switch failure caused other compressor or refrigerant line damage
  • You lack the tools, skills, or confidence for the repair

At Fix4U Repairs, our expert techs have extensive experience diagnosing and replacing faulty pressure switches in all AC system types. Call (647) 363-5205 for fast and proper pressure switch repairs.

Pressure switch issues? Call Now and Fix your AC!

Preventative Maintenance

To maximize the lifespan of your AC pressure switches and avoid unexpected failures, be sure to:

  • Have an HVAC technician annually check switch cut-in/cut-out pressures
  • Properly size the AC system to avoid extreme operating pressures
  • Keep condenser and evaporator coils clean to facilitate proper airflow
  • Promptly repair refrigerant leaks causing low pressure switch issues
  • Address any sources of condenser airflow blockage triggering the high pressure switch

With proper installation, maintenance, and cleaning, most AC pressure switches provide years of reliable service.

The Importance of Functional Pressure Switches

Allowing defective pressure switches to go unchecked is asking for catastrophic compressor failure, not to mention very uncomfortable conditions as cooling performance declines.

While pressure switch problems can stem from other issues like dirty coils or refrigerant leaks, the switches themselves are relatively inexpensive fixes that pay major dividends in system protection and energy savings.

Don’t wait until you have no cooling at all – replace suspect pressure switches at the first sign of abnormal operation.

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