No Pressure On High Side Of AC: What Happened?

The compressor is responsible for creating pressure for several parts of the car AC, including the high and low sides.

Similar to AC low side pressure high, what happens if there is no pressure on high side of AC?

This situation can cause this part to stop working, or worse, damage, spark fire, and spread to some other components. So let’s solve it now!

How Does Car AC Compressor Work? 

no pressure on high side of ac

What Is A Car AC Compressor?

The most important component of the air-conditioning system is the AC compressor.

The air conditioning system’s power unit pushes the refrigerant under intense pressure before being pumped to the condenser then transforms from gas to liquid.

An accessory belt drives most auto air conditioning compressors. If the belt slips or is worn-out, the compressor won’t operate as efficiently.

Compressor refrigerant leaks might also lessen the volume of cool air entering the interior.

If internal parts break down, there might not be any cold air. Low AC refrigerant levels in the system do not always result in AC problems.

Sometimes, it’s due to the failure in related parts, like the compressor.

How Does It Work?

Freon is a widely used refrigerant that turns hot air into cold air.

The primary function of the AC compressor, which is to compress the refrigerant used to absorb warm air inside the car’s cabin, is driven by your vehicle’s engine.

An electromagnetic clutch initiates the belt drive when the A/C system is turned on. The swash plate oscillates six double-ended pistons that control both intake and compression.

The flow of refrigerant circulates and then mixes with a fine oil mist to properly lubricate the moving parts.

No Pressure On High Side Of AC: Causes & How To Fix

Why is my high-side ac pressure low?

In fact, there are many reasons for this issue, such as the bad pressure switch, evaporator coil, etc..

You should also pay attention to the faulty compressor clutch relay, compressor pulley bearings, and AC compressor speed sensor.

What Causes Low Pressure On High Side Of AC

The compressor typically malfunctions when the clutch is at fault. The serpentine belt in your car supplies power to the AC compressor.

Your car’s various components receive the power they require from the serpentine belt. If your engine is running, the compressor will have power from the engine.

However, the pulley on the compressor continues to turn even if you don’t use the air conditioner.

The compressor features a clutch system that releases the compressor from its pulley if your AC is turned off, reducing wear on the AC.

The compressor won’t function properly if the clutch doesn’t engage when the system needs it to. And this can cause AC high side pressure too low and vice versa.

Besides, I also notice that when there is something wrong with the compressor speed sensor or the compressor pulley bearings, the no-pressure situation also happens.

I sometimes even have trouble with the compressor shutting off after a few seconds.

How To Fix It?

To handle the low high-side pressure, you can fix these three main components:

Compressor Clutch Relay

The compressor clutch relay is the first thing you may examine. It is often located in the engine bay’s fuse block. This leads to car AC high side pressure too low.

An electrical device called a relay enables modest current circuits to switch huge currents.

This allows the compressor clutch to be activated by the AC controller in the car by supplying current to the magnetic that powers it.

A diagram of the many relays and fuses inside the engine block should be on the lid. If the relay malfunctions, the compressor clutch won’t respond to the car’s interior controls.

Fortunately, changing a relay is comparable to changing a fuse. Unplug the defective relay and plug in the working one.

Compressor Pulley Bearing

The compressor pulley may seize up or move more slowly due to a worn compressor pulley bearing. When this occurs, the pulley hardly moves. 

As a result, the pulley won’t be able to drive the compressor with enough force from the serpentine belt, and it leads to AC high low-side pressure and vice versa.

This problem can be resolved by replacing the compressor’s bearing. When the serpentine belt rotates the pulley, it moves more freely, thanks to the bearing.

When a bearing is worn, it is more difficult for the pulley to turn.

And this situation can affect the AC’s balance. It results in low pressure on high side of AC and high pressure on low side AC.

AC Compressor Speed Sensor

When facing high side AC pressure low, check its speed sensor. The AC amplifier or the ECU will get information about the compressor’s speed from the compressor speed sensor.

The AC amplifier will compare the engine and compressor speeds. Its speed-to-compressor speed ratio should remain consistent.

Variations in the engine and compressor RPMs can indicate two things. First, it can signal that the serpentine belt has slipped.

A deteriorated serpentine belt may begin to sag and lose stability. This problem can be resolved by changing the belt.

Second, it can represent sliding in the compressor clutch. A bearing issue may bring on this issue.

A shortage of power supply may be the root of this problem. Low electrical energy may compromise the electromagnet’s ability to hold the compressor clutch in place.

AC High Side And Low Side

car ac high side pressure too low

High-Pressure Side

The warm air that the refrigerant draws in from your car’s interior won’t be dissipated if the air outside is hotter than the refrigerant’s temperature.

The refrigerant will lose its effectiveness as a result of this.

The condenser receives high-temperature gas from the compressor and spreads the refrigerant’s high temperature across its fins.

As you drive your car, outside air rushes through the condenser’s fins and passes through. The warm temperature is dissipated by passing the colder outside air through the condenser’s fins.

As the gaseous refrigerant moves through the condenser, it cools. The refrigerant transforms from a high-pressure gas to a liquid as a result of the release of heat.

As a high-pressure liquid, refrigerant exits the condenser and travels to the dryer.

Low-Pressure Side

The expansion valve is where the liquid refrigerant travels after leaving the dryer. It signals the beginning of the cooling system’s low side.

The service port for the AC system’s high side is between the dryer and the expansion valve. Here is where the refrigerant’s pressure on the high side is measured.

There is nothing else to pressurize the refrigerant between the compressor and the high-pressure service port.

Its expansion valve lowers the refrigerant pressure. This will guarantee that the liquid refrigerant at low side is frigid enough to cool the evaporator’s fins.

An expansion valve also regulates how much refrigerant is sent to the evaporator. Doing this lets you control the temperature in your car’s passenger compartment.

Then, the heat from the air flow is transferred to the cool evaporator fins by a blower, which forces warm cabin air through them.

The air becomes cold when it returns to the cabin because heat moves from the perspective to the evaporator.

How To Take The Pressure Readings

Always compare your AC system’s pressure measurements with a compression chart.

Remember to take the ambient air temperature before consulting the pressure chart. The low-pressure and high AC pressure gauge ranges should be noted.

You can determine the most likely cause of the issue from the results of both readings.

Next, compare the findings to the range of values on the chart after obtaining readings for both the two sides.

Only two possible outcomes are shown in the graph when the high side value is below the range of values.

The first result is when you obtain a value for both the high and low sides below the specified ranges. Your AC system has low refrigerant levels if these two conditions are present.

However, a mechanic must check for potential leaks before recharging your AC.

A low side value higher than the range and AC high-side low pressure combine to produce the second result. The compressor issue is to blame in this instance. It should be repaired or replaced.

Should you find the car AC pressure goes off, click here to remedy it soon.


high pressure on low side ac

How Much Does It Cost To Fix A Car AC Compressor?

The repair cost will be affected by many different factors. It will be the problem you are facing—labor cost, cost of materials and the service fee of the repair facility you choose.

Depending on the area, the price can vary from a few dozen to a few hundred dollars.

For repairs, you will expect to pay between $700 and over $1000. Of course, replacing a new one will cost much more.

The cost of fixing the AC compressor in your car spans from $800 to $1,500. You should prepare about $1,150 to replace this part.

The fees can be lower if you’re fortunate: the AC compressor is simple to access, the part is from an economical brand, and it’s offered as a refurbished or aftermarket part.

What Causes Low-Side Pressure Too High?

Contrary to no pressure on the high side, AC high pressure on low side will also give you a headache.

The transition between the two sides is likely where the issue is. Its condenser or condenser fan could be having a problem.

After the compressor, the condenser is the first part of the AC system. The temperature and compression should decrease as it ascends to the expansion valve.

Let’s say there is a problem with it or the fan. To this end, it can fail to cool the refrigerant, leaving the pressure after it has gone through the evaporator greater than expected.

An overcharged system is another reason for this circumstance. When the AC system is re-gassed, every car is built to take a specific amount of oil and refrigerant.

You must add the appropriate quantity, like all the other required fluids in a vehicle.

What If I Continue Driving With Abnormal AC Pressure?

In the least dangerous situation, your compressor could stop working suddenly at any time. This is extremely inconvenient, especially on long trips or deserted places, with few repairing tools.

The overloaded compressor can be more dangerous, causing severe damage to other components. The worst case can pose a fire risk.

Final Thoughts 

In general, no pressure on high side of AC is a common situation that you may have to face. As it’s complicated, this should be solved by professional mechanics

Last but not least, when you have to face the AC high side pressure low or vice versa, fix the bad compressor as soon as possible to avoid more serious damage to the system and other components.

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