A/C Pressure Drops When Compressor Turns On: What to Do?

A/C Pressure Drops When Compressor Turns On

Introduction to the topic

The failure of the air conditioner’s pressure switch can result in the failure of the entire cooling system. How to recognize a faulty air conditioning pressure switch

Most drivers don’t give their air conditioner’s pressure switch a second thought until something goes wrong, and if you’re unlucky, fixing it may be a major hassle.

Identifying the location of a faulty ac pressure switch is our focus today, and we’ll take a look at the indicators that indicate a problem. Furthermore, we cover the potential replacement cost and how to test for a faulty ac pressure switch.

The diagnosis of some of these symptoms will be simpler than others. There are also a few error codes that can be found in an air conditioning system that may help you figure out what’s wrong. Let’s check out the most typical symptoms.

Why is my car ac blowing warm air?

When a car’s air conditioner breaks down, the most common complaint is that warm air is being blown. Several factors may contribute to this condition:

  • Low refrigerant levels in an air conditioning system
  • The compressor won’t start due to an electrical issue.
  • Inefficiency within the system
  • Issues with the climate regulation system

To begin, we will focus on the most prevalent issue, which is a deficiency of refrigerant, and explain how to utilise pressure measurements to determine the amount of refrigerant present and its location. After that, we’ll discuss other potential system issues.

When does a faulty ac pressure switch show itself?

A faulty ac pressure switch will typically exhibit the following symptoms:

  • The ac only works intermittently
  • The ac has stopped working.
  • The wind is warm
  • Noises from the ac unit that don’t make sense

Take a look at this more in-depth list of the most common indicators of a malfunctioning ac pressure switch to figure out what’s wrong and how to fix it:

1. Temporary AC units

This sign of a failing air conditioning system might manifest itself in a number of different ways. It’s possible that during startup, you’ll experience a brief system shutdown. On the other hand, it may not operate at all or only intermittently, leaving you sweaty and uncomfortable.

In any case, sporadic use of the air conditioner is indicative of a defective ac pressure switch. You’ll need a new switch installed to restore your ease and convenience.

2. A/C won’t turn on

What could be worse than ac that doesn’t operate consistently? When does it completely stop working? The sensor for the refrigerant pressure switch could be broken if your air conditioner won’t turn on.

Although there are numerous potential causes for ac issues due to the system’s complexity, yours may be unique.

3. AC is blowing warm air

A cool blast of air is what you anticipate when you flip the switch on the air conditioner. But if the ac pressure switch fails, you might only get warm air.

But low refrigerant levels, which should be checked routinely, are another common cause of this issue.

4. Weird noises from the AC

If the compressor is intermittently turning on and off, you may hear some unusual noises coming from the engine and the area beneath the dashboard. There will be a clicking sound, similar to when the compressor normally engages, but no air will be produced.

To identify if the switch is turning the compressor on or off, pay attention to the clicking sounds coming from under the dashboard and the engine bay.

What to do when taking your pressure readings?

This condition is brought on by a confluence of factors. Specifically, there is a one-to-one relationship between the pressure and temperature in the system. The pressure of the refrigerant at a specific temperature can be determined. One can look up an online refrigerant pressure temperature chart.

Connect a pressure gauge set to the ac system and take readings from both the low- and high-pressure settings. See if the pressure readings you took coincide with the readings on the pressure chart by checking the surrounding temperature.

If the readings are consistent, you know the freon content is safe. If the gauge’s reading is higher than the chart’s, the system is overcharged, and if it’s lower, the refrigerant level is low, suggesting a leak. On the other side, when the pressure is zero, there may be a massive leak.

How to analyzing an ac pressure switch?

A multimeter can be used to check the functionality of an ac pressure switch. Measure the resistance between the signal pin and the ground pin using the ohm setting on your multimeter. When the switch is closed, there should be no open circuit and the ohm reading should be 0. However, the proper values for your vehicle model can be found in a repair manual.

Additional procedures for checking an ac pressure switch are as follows.

First, activate the air conditioner

Don’t switch off the engine, but crank up the air conditioner. Keep the windows open so the air doesn’t just keep recirculating inside.

Inconsistent shutoffs are the first symptom of a failing air conditioner pressure switch. In no world does this occur with the windows wide open.

Look for error messages

You can use a code scanner to look for dtcs if your car has an obdii port. When the issue has been resolved, the codes can be removed using the code scanner.

You can check with your neighbourhood auto parts store to see if they will read your engine’s codes for free if you don’t have one.

If a fault code appears on the ac pressure switch circuit, you should check the continuity of the wires leading to the switch. If the pressure warning comes up, it could be due to a lack of refrigerant.

The results from the pressure sensors can be seen with the scanner, as many newer automobiles feature an electronically controlled ac system. Simply turn on the air conditioning, plug in your obd scanner, and examine the readings from the ac pressure switches.

Third, make sure all electrical connections are secure.

If your vehicle doesn’t have an ac system scanner, you’ll need to check the system yourself. It is recommended to start with a wiring diagram and repair manual tailored to your make and model of vehicle.

It’s important to know if your ac pressure switch has two or three wires. Typically, a two-wire setup consists of a signal line and a ground wire. If there are three, there will likely be a 5-volt line, a signal wire, and a ground wire. However, a wiring diagram is required to verify this.

Use a multimeter to verify the resistance (in ohms) between the signal pin and the ground pin. When the switch is closed, there should be no resistance and when it is open, there should be a complete circuit. When the ac pressure is correct and everything is running smoothly, the switch will normally be closed.

Checking the ac pressure switch connector for 5 v, ground, and an engine control module signal is also possible. You should inspect the wiring if the values seem off. The lack of a wiring diagram prevents this, though.

Verify the air conditioner’s pressures

If the pressure switch on your air conditioner looks to be working well, use a gauge set to ensure that the temperature and pressure within your home are both within safe ranges. The low-pressure gauge goes into the low-pressure fitting, and the high-pressure gauge goes into the high-pressure fitting.

At or below 90 degrees fahrenheit, low pressure readings should hover around 30 psi. The high-pressure side, where an extra 50 psi has been supplied to the atmosphere, should be about twice as hot as the surrounding area.

There may be a greater issue with the system, or you may need to refill the refrigerant, if the low or high pressures are off.

Estimated fee for replacing a faulty ac pressure switch

Alternating current (ac) pressure switches typically cost between $50 and $300 to replace. The cost of the ac pressure switch itself is probably going to be somewhere in the neighbourhood of $0 to $100, while labour may run you anywhere from $30 to $200, depending on how challenging it is to get to the sensors.

There is a check valve inside the ac pipe that prevents the refrigerant from pouring out, so in most situations you won’t need to empty and refill the coolant system while changing the ac pressure switch.

Carefully removing the air conditioner’s pressure switch can reveal if this is the situation for your vehicle.

Watch Symptoms of a bad AC pressure switch | Video

People also ask questions and answers related to A/C pressure drops when compressor turns on

Exactly what does the ac pressure switch regulate?

The low and high pressure sides of an ac system are constantly monitored via pressure switches. If the pressure on one side of the switch rises too high or falls too low, the compressor that powers the air conditioner won’t run.

Can an ac pressure switch be turned off manually?

If your car utilises an older style of ac push switch with two pins, you can simply run a wire between the pins in place of the switch to disable it. However, doing so is not advised because it could cause serious damage to the system. You should first consult a repair manual and a wiring diagram.

How to find out whether the pressure switch on my air conditioner is malfunctioning?

You should replace your ac pressure switch if the system cycles on and off frequently, does not effectively chill the interior, or does not activate the compressor.

How can i check the health of my air conditioner’s compressor?

Warning signs your ac compressor is failing
The air conditioner’s compressor is broken.
The heater is on and the air conditioner is on.
The circuit breaker keeps getting tripped because of the air conditioner.
When turned on, the external unit causes a trembling sensation.
Weird noises are coming from the ac unit.

Does the air conditioner need to be running when you check the pressure?

Not at all; it won’t give you an accurate reading. Measure the pressure in a vehicle after turning off the engine and turning off the air conditioning for at least an hour; this will allow the pressure to equalise (both high and low) and give you an accurate reading.


The air conditioner’s pressure switch is a crucial component. It’s crucial to get it fixed as soon as possible if it stops working correctly because the cost of fixing it could add up quickly.

Since releasing refrigerant into the air is very terrible for the environment and there are some dangers to handling the refrigerant, working with air conditioning systems can be difficult, and even illegal, in some countries. If you don’t feel confident repairing ac systems, it’s best to take your automobile to a professional.

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