Symptoms Of A Bad AC Pressure Switch (High Or Low Pressure)

Your car’s AC pressure switch monitors refrigerant pressure inside the air conditioning system and cycles the compressor (the part that “pumps” the refrigerant) off/on to adjust. Ultimately, the purpose of an AC pressure switch is to protect the compressor.

If pressure is too low, the AC compressor may not receive enough oil, and if it’s too high, it may overheat.

There are two halves to an AC system, the low-pressure side and the high—each has its own AC pressure switch. A faulty pressure switch may damage the AC compressor and halt the refrigerant flow, causing your AC to stop blowing cold air.

What are the symptoms of a bad AC pressure switch? 

The three most common signs include:

1. AC struggles to cool the cabin/blows warm air
2. AC makes excessive noise
3. AC stops working or cycles off/on

This guide provides more details on each of these symptoms. We’ll also answer some frequently asked questions about AC pressure switches, including:

• How long do AC pressure switches last?
• Where is the AC pressure switch located?
• How do I test an AC pressure switch?
• Can you drive with a bad AC pressure switch?
• How much does it cost to replace an AC switch in a car?

Learn more about how a car’s AC system works in our detailed guide. Prefer a visual explanation? Check out this video from YouTube’s Ratchets and Wrenches.

Symptoms Of A Bad AC Pressure Switch

1. AC Struggles To Cool The Cabin/Blows Warm Air

A healthy air conditioning system should quickly cool a car’s cabin after a few minutes. But if an AC pressure switch is failing (low- or high-pressure), it can harm the AC compressor.

A damaged compressor may struggle to cool the vehicle’s interior fully. You may even feel warm air blowing from the vents on scorching days.

2. AC Makes Excessive Noise

Another bad AC pressure switch symptom is hearing excessive noise while the air conditioner is running. Specifically, you may hear “clicking” sounds from the engine compartment and below the dashboard.

This stems from the compressor’s clutch not fully engaging. As the issue worsens, it may become more of a “rattling” or even “screaming” as the pump inside the compressor free spins.

3. AC Stops Working Or Cycles Off/On

Finally, if your car’s AC cycles off and on or stops working altogether, either the high- or low-side pressure switch may have failed.

You’ll notice other bad AC pressure switch symptoms first, like clicking sounds or the system struggling to keep the cabin cool. Unfortunately, if the problem gets this far, you’ll likely need to replace the compressor.

Bad AC Pressure Switch FAQ

How Long Do AC Pressure Switches Last?

AC pressure switches are rated for up to 50,000 cycles, with each cycle equal to roughly 15 to 20 minutes of air conditioning. For most drivers, this means AC pressure switches should last a vehicle’s lifetime—unless the AC is constantly running.

Where Is The AC Pressure Switch Located?

Cars have two AC pressure switches, one for the low-pressure side and one for the high-pressure side. To find your car’s AC pressure switches, follow the AC lines coming from the compressor. The smaller line leads to the low-pressure switch, while the larger line leads to the high-pressure switch.

How Do I Test An AC Pressure Switch?

Testing your car’s AC pressure switch entails plugging an OBD II code scanner into the OBD port and checking the system for error codes. Some of the most common error codes associated with a faulty AC pressure switch include P0530, P0531, P0532, P0533, P0745, P0746, P0747, P0748, and P0749.

Can You Drive With A Bad AC Pressure Switch?

Yes, you can drive a car with a bad AC pressure switch. The compressor is the only part directly affected by the AC pressure switches. So, if a switch fails, the compressor may also, but the rest of the car will run the same as usual—albeit without AC.

How Much Does It Cost To Replace An AC Switch In A Car?

To replace an AC pressure switch, repair shops usually charge for one hour at a rate of $75 to $130. Expect to spend between $15 to $50 on parts. Add parts and labor, and the total cost of replacing a bad AC switch (low- or high-pressure side) comes should range from $90 to $180.

Keep Repair Costs Low By Promptly Addressing Bad AC Pressure Switch Symptoms

There are many reasons your car’s AC might be blowing warm or hot air, and a bad AC switch is just one of many potential causes. The only way to tell for sure is to scan the system for error codes using an OBD II tool.

If you address any bad AC pressure switch symptoms as soon as they appear, repair costs shouldn’t exceed $200. However, if too much time passes, you may need to replace the AC compressor, a job that costs about $800 on average.