Car AC Low Side Pressure Zero – Explained

Car AC Low Side Pressure Zero – Explained

Driving on a hot summer’s day in your car without an air conditioner can be inconvenient and even severe in some circumstances.

Knowing the exact reason why it doesn’t work can be a handful and can cost you less than going to a repair shop.

Car AC Low Side Pressure Zero GÇô Causes and Solutions

But what can you do if you end up with a car AC low side pressure zero after your diagnosis?

There are several reasons why you are experiencing a car AC low side pressure zero.

Correcting it might be tricky because you need to go through each air conditioning component one by one.

Here’s a guide that can help you with this problem.

7 Causes Of Car AC Low Side Pressure Zero

1. Bad AC Compressor

The compressor is the component of your AC system that generates the pressure that your car’s coolant or refrigerant is subjected to.

Usually, this would be the first to investigate if you have problems concerning a pressure issue in your AC system.

If you have been experiencing a noisy compressor before the total shutdown of your air conditioner, then you may have issues with the AC compressor in the first place.

A bad thermal limiter on the compressor can also be the reason, and possibly it is due to the heat of the alternator.


The first thing you would do to determine the problem is pressure test your AC system.

After checking everything and everything else fails, you need to replace the compressor to fix the unit entirely.

2. Clogged AC System

The temperature of your AC system can produce cold air is directly tied to the entire system’s pressure.

The refrigeration portion of your air conditioner must be operating at the proper pressure to generate the needed temperature to cool the car.

It is worth noting that if you have a car AC with low side pressure zero, it strongly indicates that the side is in a vacuum, and the primary cause is a blocked component in your AC system.

You may also want to check your expansion valve located against the firewall inside your car for something could be stuck in it.


Flush everything out to remove the blockage. You may use a suction vacuum pump to pressure the system and remove all the moisture in its components.

Make sure that you have flushed every area that you can find to make your AC work again.

3. Expansion Valve

This tube acts to control the quantity of refrigerant to flow into the evaporator.

More refrigerant is sent to the evaporator when its aperture is enlarged above its standard size, resulting in pressure discrepancies such as car AC low side pressure zero.

In such cases, you may encounter that your compressor is still good while having a car AC low side pressure zero.

It means that it is still attempting to extract the refrigerant gas from the evaporator.

However, a clogged expansion valve will prevent the high-pressure refrigerant liquid from dispensing into the coil resulting in a car AC low side pressure zero.

Your expansion valve could not have been opened due to recent changes in the components.

If you have recently changed it, it may be the culprit of a car AC Low side pressure zero. Or it may be the sealants clogging some area of the valve.


Check your expansion valve and ensure it is in place. Clean everything up from the bottom to top to ensure no clogged components in between.

Replace your dryer/receiver to make it work again. Nonetheless, this component should need to be changed and replaced every time your AC system has been opened.

It also increases refrigerant flow to make things icy cold on your car’s inside.

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4. Damaged Condenser

One of the common reasons for a car AC low side pressure zero is a damaged condenser. It may have a leak to which the refrigerant is located.

In some cases, when a compressor is damaged, it does not cycle naturally. Similarly, this issue will also occur when the seal of the o-ring on the exterior of the orifice expansion tube fails.


You will need a thorough pressure check to see if you have a damaged condenser. You can also check if leaks are using a UV penlight.

A better option to check leaks is to use a dye, and when you find one, you need to reinstall the evaporator and put new o-rings on both ends.

Adding to that, you need to change the valve cores.

5. Low Refrigerant Charge

If your car’s engine is running and you found that the gauges indicate a very low to zero pressure and felt warm air escaping through the vents, then your AC system is running short on refrigerant charge.

Remember that running on a half or the low charge will eventually destroy the compressor, and that will cause more problems in the long run.


Make a thorough clean-up and evacuate the AC system to check any blockage, then have the proper amount of refrigerant to recharge the whole system fully.

6. Bad Connection To The Gauge Hose


To check if you have a bad connection, you can do this method. First, connect the manifold to your car, attach the yellow line to the suction pump, and start it.

Initially, the high side valve should be opened, and you can observe the low side gauge enter vacuum.

It will indicate that the pump is sucking air through the high side hose from the car. It means that it detects a growing vacuum via the low side hose.

As a result, you’ll know that both valves are open. Once that is correct, open the low side valve to finish the evacuation.

This method is recommended at each evacuation to ensure that you are really linked to the car’s AC system and not just draw a vacuum in each of the hoses.

7. Fan Problems

It is conceivable that something like debris has obstructed the airflow coming from one of your condenser fans’ motors, or in some instances, it has been damaged entirely.

It reduces the airflow via the condenser, which means it will not cool the AC system unit. The reduced airflow might indicate the cause of having a car ac low side pressure zero.

If the condenser fan is subjected to excessive pressure, it might deform the aluminum component, thus resulting in evaporator coil leakage.

It has the potential to ruin your AC system completely.


First, you need to go inside your AC system and check the circuit breaker, for it might be that your compressor comes to a halt because there is no electricity for it to run.

Next is to look at the contactor’s voltage to see if the compressor is getting power. If the problem persists, you need to check the air filter to investigate clogs in the system.

If everything fails, you might need to call a technician to fix you.

Final Thoughts

In every automobile, the air conditioning system is one of the most complex components.

Various issues might arise when air conditioning fails to operate correctly or operates at a reduced capacity.

And for many drivers, this is something they may overlook for the time being since air conditioning is not necessary for a car to operate well.

That’s why you need to schedule a maintenance check-up once in a while to avoid the expensive cost that any problem may bring, such as a car AC low side pressure zero.