What Causes High Pressure Lockout on a Heat Pump?

Heat pumps are an excellent alternative to traditional HVAC systems, but they can also experience issues. One particular issue is high-pressure lockout. A high pressure lockout is a safety feature that can prevent you from using your heat pumps correctly. But what causes high pressure lockout on a heat pump, and how can you avoid it? Our experts can answer this question and more. Contact JC Mechanical to speak to Denver’s reliable heat pump maintenance team!

Denver’s reliable heat pump maintenance

What Is High Pressure Lockout on Heat Pumps?

High pressure lockout is a safety feature on modern heat pumps in which the system automatically shuts off if internal pressures rise too high. The point of high pressure lockout is to prevent your heat pump from sustaining damage by operating outside of normal pressure parameters. High pressure lockout is a built-in safety feature, so it is not a malfunction of your air source heat pump

High pressure lockout switches work by shutting off the compressor — the main unit that pressurizes coolant fluid. Shutting off the compressor keeps pressures from rising and damaging refrigerant and drain lines. The system shuts off the compressor when internal static pressures exceed the relief pressure — that is, the rate at which the system can relieve pressure. 

Most heat pumps use two specific types of high pressure lockout switches:

  • Wall-mounted pressure switches attach to a separate pressure pipe and have a mechanical arm that moves when pressure exceeds a certain threshold. You can modify these kinds of switches to allow for higher pressures. 
  • Cartridge pressure switches attach to the coolant line and have a fixed internal design. The fixed design means you cannot modify pressure settings to allow for higher pressure.

In addition to the high pressure switch, most heat pumps have a low-pressure switch that serves a similar function. 

How to Tell Your Heat Pump Is Locked Out

Similar to car engines, modern heat pumps have internal computers that keep track of components. When something goes wrong, the system sends an error code to denote the problem. For example, Carrier heat pumps and HVAC systems use Error Code 84 to denote high pressure lockouts. 

More generally, most heat pumps and HVACs display error codes through flashing LED lights. The lights might be located inside the unit or on the outside of the casing. You can cross reference flashing LED patterns with the heat pump’s user manual to determine what error code the system is sending. 

If you can’t decipher the flashing error code message, you can call a professional HVAC technician to diagnose the issue. Technicians have equipment specifically for detecting and looking up heat pump error codes. 

What Causes High Pressure Lockout?

High pressure lockout occurs when internal pressure rises too high. This could be due to a number of reasons, such as the following.

Clogged Condenser Coil

Perhaps the most common cause of a high pressure lockout is a clogged condenser coil. Condensing coils are components that transfer heat from refrigerant to the outside air, removing it from your house. When the coil becomes clogged, that heat and pressure have nowhere to go. The pressure rises, tripping the lockout switch. 

You can fix the issue by cleaning your coils regularly. You can clean coil arrays using a soft-bristled brush with a simple mixture of detergent and water. Afterward, leave the coil to dry in the air before turning the heat pump back on. 

Dirty Air Filter

Clogged air filters can also cause pressure levels to rise too high and trigger an automatic lockout. The dirt and debris in a filter restrict airflow, which means the system can’t vent excess heat adequately. Moreover, a dirty air filter can be a fire hazard if heat levels get too high. 

Replacing the filter should reduce the pressure back to adequate levels. We recommend you change your heat pump air filters at least once every year or once every six months. Doing so will keep airflow high and prevent the system from overheating. 

Blocked Refrigerant Tube

Your refrigerant system has capillary tubes that regulate coolant fluid flow. These tubes can become clogged by sediment and debris, which stops the flow of refrigerant and raises the pressure in the lines. If the pressure in the capillary tubes is too high, they can crack and cause coolant fluid leaks. 

You can keep your refrigerant lines clean by flushing them with nitrogen-based cleaner. You can also hire a professional to clean your drain lines while they are performing general heat pump maintenance. 

Incorrect Refrigerant Amount

Another malfunction that causes high pressure lockout on a heat pump is having too much or too little coolant fluid. When fluid is too low, the compressor can create too much pressure and shut the system down. You should never have to change the level of coolant fluid, so if levels are too low, it means you have a leak somewhere in the coolant lines. 

Bad Pressure Switch

Alternatively, a high pressure lockout could be due to a bad pressure switch. Normally, the switch is set to a specific pressure level. If it’s broken, it could be the pressure switch tripped at a lower pressure level than it should. The result is a high pressure lockout, but there is nothing actually wrong with pressure levels. 

The solution here is to regularly service and test your pressure switches. Pressure switch testing is usually part of a typical heat pump maintenance session. If your technician discovers a problem, they can replace the switch. 

Resetting a High Pressure Switch

The high pressure switch is supposed to shut down the compressor when pressure gets too high. If your system shuts down, one possible solution is to reset the pressure switch. You can reset the switch by pressing the reset button on the heat pump control panel. Most of the time, the reset button is underneath a plastic cover you’ll have to remove to press it. You may have to use a flashlight to locate the button. 

Can I Bypass a High Pressure Lockout?

Technically yes, you can bypass a high pressure lockout by adjusting the pressure switch or removing it. However, you should never try to bypass a lockout, as it can be extremely dangerous. Bypassing the switch means the pressure in the unit can rise so high it can cause permanent damage. High pressure can also pose a safety hazard. 

Heat Pump Lockout FAQ

Below are some of the most common questions we receive about high pressure heat pump lockouts. 

How Can I Prevent Heat Pump Lockouts?

The best way to avoid high pressure heat pump lockouts is to get regular maintenance. Maintenance will handle all the problem areas that can cause a lockout, like changing air filters and flushing out drain lines. Maintenance will also help identify issues before they can cause a lockout. 

What Should I Do If My Heat Pump Is Locked?

If your heat pump is locked, you should call a professional HVAC contractor as soon as possible. Your HVAC contractor can diagnose the issue and fix it to get your system back in working order. 

How Does High Pressure Lockout Affect the Heat Pump?

The main side effect of a high pressure lockout is your system will effectively lock itself, so you can’t heat or cool your home. You need to get internal pressures back to normal operational levels before you’ll be able to use it again. 

Denver’s Top Mechanical Experts

Now that you know what causes high pressure lockout on a heat pump, read our blog to learn more about common heat pump problems. Fill out a contact form, or call JC Mechanical at (720) 594-5588.

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