Signs Your A/C System Is Low on Refrigerant

Mia Bevacqua
August 30, 2018

Air conditioning is based on thermodynamics — heat always moves to a cooler state when possible. It’s simple science that keeps you cool when driving on a scorching afternoon.

In your car, the refrigerant actually removes heat from a vehicle’s cabin. Because it has such a frigid boiling point (below 0 degrees Fahrenheit), refrigerant is able to absorb heat at low temperatures.

Symptoms of a refrigerant problem

When the refrigerant level is low, it can cause several problems. You can always get an AC diagnosis at a shop, but these are the most common symptoms:

1. Lack of cooling

The primary symptom associated with a low refrigerant charge is that the air blowing from the vents isn’t cold. Instead of that cold blast, the A/C system spews warm or hot air.

2. Rapid cycling of the compressor clutch

This can be heard as a clicking noise followed by high-speed radiator fan operation and surges in engine idle speed.

3. A/C warning lights

In some vehicles, an A/C warning light will come on when there’s a problem with the system. For example, some Toyota vehicles will flash the A/C button on and off to indicate an issue.

4. Signs of refrigerant leaks

You may be able to spot a refrigerant leak — look for traces of oil on A/C components, especially near the crimped ends of the rubber AC lines, and around the compressor. In most cases, however, leaks are hard to spot with the naked eye. Professionals use an ultraviolet light and goggles to spot dye leaking from the system. An electronic leak detector can also be used.

Get it diagnosed by a professional

Book an appointment at a shop in your area

What are some common types of refrigerant?

In the past, A/C systems used a type of refrigerant called R12, or Freon. Although many technicians still incorrectly refer to refrigerant by this name, Freon hasn’t been in circulation for years — it’s bad for the Earth’s ozone layer.

Most cars made starting around 1995 use R134a, which is better than Freon but is still classified as a global warming gas. Because of this, automakers are starting to make the transition to R1234yf, which is touted as being more environmentally friendly. Another option, R152a is slightly less dense than R134a, so it can result in better fuel economy.

Every type of refrigerant has oil mixed in to lubricate the air conditioning compressor. The kind of oil used depends on the type of refrigerant. On cars made in the last couple decades, trace dye is also added to the refrigerant to allow for easy leak detection.

» LEARN MORE: Get an estimate for your refrigerant problem

How to fix the problem

The air conditioning is a sealed system. If the refrigerant is low, it means there’s a leak somewhere, even if it’s minuscule.

The best way to fix it is to have a professional evacuate and then recharge the system. This process involves using specialized equipment to remove old refrigerant, moisture and air from the system — this is called evacuation. Then the system is recharged with new refrigerant by adding the exact volume specified by the manufacturer.

A technician will check the orifice tube or expansion valve, then check for system leaks and other problems before recharging the refrigerant.

How refrigerant works

To better understand the role of refrigerant, it's helpful to have an overview of A/C system operation.

  1. Refrigerant first starts out as a high-pressure liquid that is sprayed through a metering device and then allowed to rapidly expand into a low-pressure vapor as it enters the evaporator core — kind of like a small radiator located in your dash. A blower motor pushes air through the evaporator fins, causing the refrigerant to boil as it absorbs heat from the cabin, and turn into a vapor. This portion of the system is known as the “low side,” but is still under pressure.
  2. As a vaporized, low-pressure gas, the refrigerant leaves the evaporator and enters the receiver-drier before it heads to the compressor. The compressor pressurizes the vaporized refrigerant and increases its temperature. Because it had already boiled in the evaporator, the heat of compression has turned it into a superheated gas. This section is known as the “high side” and is under very high pressure.
  3. The refrigerant then leaves the compressor and enters the condenser, another radiator-style component that sits behind the vehicle’s grille, in front of the engine radiator. When the car is moving down the road, cool air is pushed through the condenser. This removes the heat and causes the refrigerant to turn back into a liquid.
  4. On the final leg of its journey, the refrigerant travels through a metal tube back to Step 1 above, where it enters either an orifice tube or thermostatic expansion valve. Both of these components create a restriction that reduces the refrigerant pressure as it rapidly expands into the evaporator core. It then enters either the receiver-drier or accumulator before restarting the process.
Mia Bevacqua

About the Author

Mia Bevacqua is an automotive expert with ASE Master, L1, L2 and L3 Advanced Level Specialist certification. With 13-plus years of experience in the field, she applies her skills toward writing, consulting and automotive software engineering.

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