AC Compressor Running But No Pressure Change: 8 Root Causes

It’s a daunting feeling when you are left with an AC compressor running but no pressure change. This is a clear indication that something is not right in your car AC.

This may stem from multiple culprits, such as a refrigerant leak, a faulty compressor, a fluid leak, an AC clutch, or a clogged expansion valve.

Whatever the cause, it’s core to address the issue promptly to avoid further damage to your AC system.

Here comes a list of reasons and viable measures for your reference, besides some precious tips. Let us get your back!

Why Is The AC Compressor Running But No Pressure Change? The Solutions

ac compressor running but no pressure change
What Causes AC Compressor Running But No Pressure Change

There are eight triggers leading to the AC compressor not building pressure, including bad compressor clutch, faulty gasket, failed pump, expansion valve blockage, compressor pulley bearing, ac compressor speed sensor, compressor clutch relay, and compressor with an internal leak.

Compressor Clutch Failure

When the AC compressor engages but no pressure change, check to see if the compressor is indeed operating.

The compressor clutch will click and spin when you switch on the air conditioning. If it doesn’t and leaves a whining or screeching sound, repair it soon.

When the AC’s clutch is broken, it can be fixed without new buying. Yet, once the compressor clutch isn’t functioning, it implies the compressor is also in poor shape.

Replace the entire unit at once.

Faulty Gasket

If the AC compressor doesn’t turn on or it just produces meager pressure, perhaps your compressor gasket is wrong.

The gasket (between high-pressure and low-pressure compartments) regulates the compressor’s airflow pressure.

Change the gasket in that case. That can cost you a bit, so it’s wise to consider the expense before getting the replacement.

Failed Heat Pump

Inspect whether you get a defective pump. When the compressor sometimes kicks on with a faulty pump, it primarily results in the AC compressor not starting.

Also, examine manually to see if any air is escaping from it. Remember to wear safety gloves, as this air intake pump can be overly hot.

Change another one if needed to make your AC work again.

Expansion Valve Blockage

Have a look at the valve. Is it clogged with debris? This can lead to the AC compressor not running.

Inside your dashboard, adjacent to the evaporator, is the expansion valve. It’s conveniently located inside the glove box.

Switch to a new one once it ceases functioning.

Compressor Issues With Wrong Pulley Bearing

The pulley may slow down or lock up due to a failed or worn-out compressor pulley bearing. The pulley may be hardly moving though turning on the AC will force your clutch into position.

It leads to the A/C compressor not turning on since the pulley won’t have access to adequate energy from the serpentine belt.

Just change this bearing to resolve the hurdle. With a satisfactory bearing, the serpentine belt spins the pulley more efficiently.

Failed AC Compressor Speed Sensor

The AC amplifier or ECU (Engine Control Unit) will receive information from the compressor speed sensor about the compressor’s speed.

This sensor is located behind or at the compressor’s bottom.

The AC amplifier compares the engine and compressor’s speeds. The ratio between these two values should be constant.

There are two possible meanings for a change in the engine and compressor’s RPM.

Firstly, it can indicate that the serpentine belt has slipped. A deteriorated serpentine belt may begin to slip and lose stability.

To solve this matter, change the defective one to help your compressor back to normal function.

Secondly, it can hint at sliding in your compressor clutch. This issue may result from a bearing failure or lack of a power source.

Based on the situation, change your bearing and fix or change the battery if needed.

Broken Compressor Clutch Relay

A relay enables modest current circuits to switch huge currents. As such, the AC controller can activate the current powering your electromagnet to activate your compressor clutch.

The compressor clutch may not respond to the controls inside the automobile, and the AC compressor does not turn on if the relay malfunctions, halting the AC compressor from working.

Thankfully, changing a relay is relatively easy. Just unplug the defective relay and plug in the working one.

Compressor Leak

It’s problematic in case of the AC compressor not coming on with unusual noises. You can hear the leaking, metallic, or rattling sounds while using a compressor.

Check this component for any apparent leaks. Replace your leaking part or use leak sealers if possible.

Leak sealers also work in solving immediate or temporary situations. Yet replacing is always preferable in the long run.

Feel free to seek expert assistance or head to the authorized service center while you have trouble.

Try to sort the problem out soon to impede potential damage to other vehicle parts, like the intake filter, electrical fuse, suction hose, internal service ports, piston rod, pressure valve, and O2 sensor.

How To Understand Pressure Readings?

ac compressor not building pressure
Ways To Read Pressure

To identify the issues inside your AC compressor and entire AC system, always compare your AC’s pressure readings with a pressure chart.

To begin with, take the ambient temperature (ambient temps) before examining the chart. Take note of both the low-pressure and high-pressure gauge’s pressure ranges.

These values can tell you what triggers the malfunctioning air-conditioning system. Compare the findings to the chart’s corresponding range of values.

Only 2 possible results can come out:

1. The values for the high-pressure and low-pressure sides go below their standard ranges. It implies that the air conditioner is running low on liquid refrigerant pressure.

Contact a well-trained mechanic or technician. He must look for potential air leaks before recharging the refrigerant.

The leak needs fixing soon to avoid experiencing the same issue and losing refrigerant someday.

2. A low-pressure side value is greater than the provided range, and a high-pressure side value gets lower. In this case, you may get an erroneous compressor.

You have to conduct its upkeep or replacement at once to avoid your car AC from ceasing work in hot weather or in any harsh conditions.

What Are Tips To Prevent AC Compressor Not Cooling In The Future?

ac air compressor not turning on
Tips To Prevent AC Compressor Not Cooling

Let’s look at some tips to minimize visible damage to the AC compressor motor and halt it from malfunctioning:

  • Run your AC for around 10 mins once a week.
  • Use the defrost mode for 5-10 mins to eliminate extra moisture and prevent mildew.
  • Check frequently to ensure there is enough compressor oil inside the component.
  • Every two years, refresh the cooling system’s lubricant and gas supply.
  • Clean the radiator every 3 months. An overheated radiator can ruin your AC condenser.
  • Ensure your AC compressor is in good working order by performing regular inspections. Likewise, perform any necessary upkeep.


How Long Does It Take For An Air Compressor To Build Pressure?

In most cases, it shouldn’t take more than 2 to 5 minutes.

Still, since no two air compressor types are identical, the time it takes for the pressure to be built will vary. A compressor tank can be filled with air faster with a better CFM.

Also, the bigger the tank is, the more air must be compressed to fill a tank, taking more time to complete.

How Can I Test My Air Compressor Pump?

Pressurize your system until it reaches its normal working pressure by turning on the compressor. Your compressor should be left unloaded and not reloaded.

Observe how your compressor operates. If there is a leak inside, it creates no pressure.

What Happens If The AC Pressure Switch Goes Bad?

AC’s rapidly switching on and off

With the defective switch, the AC unit can turn on and off randomly – too frequently or more quickly than usual.

The car cannot be cooled

The system will have trouble keeping the pressures at the compressor necessary for regular operation once your pressure switches fail.

It’s unable to cool your car accordingly. You must go for the replacement switch in this case.

The compressor won’t turn on

Since the pressure switches regulate the compressor’s on/off functionality, a power switch failure could render the compressor inoperable.

What To Tell If My AC Compressor Is Dying Out?

Here are some sure signs of a bad AC compressor:

  • Chattering, rattling, rumbling, or ticking sounds
  • There is no airflow or just warm air is produced
  • A refrigerant leak from the compressor
  • The circuit breaker keeps tripping
  • The entire car vibrates when it cranks up

Once you notice these symptoms, bring your car to a repair shop to diagnose and tackle the problems timely. It helps to halt further grave hassles later on.


Have you ever experienced a situation of the AC compressor running but no pressure change? It can leave you feeling helpless and low on the go, notably if you live in a hot climate.

There could be several reasons, as stated. Each trigger has its resolution to tackle it all. Follow the steps to handle the hurdles and get your AC compressor back in working order soon!

Do not hesitate to share this post with other car owners; they can avoid the issue better.

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