Diagnostic Tips When Air Conditioning Isn’t Working

When summertime hits, repairs to your car’s A/C system get moved up the to-do list, fast. Here are some tips to guide you through the diagnostic process, along with information about when to replace the A/C compressor or recharge the A/C system.

A/C button in carSource | Mattes/Wikimedia Commons

Troubleshooting the A/C compressor

First, you need to eliminate the clutch in your A/C compressor as the culprit. Turn on your A/C and fans to the max setting. Is the clutch engaging? If not, use a voltmeter to see if the compressor is receiving voltage.

If there's voltage, the clutch may be bad. Replacement of the clutch and/or compressor may be necessary. If there's no voltage, there may not be sufficient refrigerant in the system to engage the low pressure cut-off switch that cycles the compressor. If it seems likely that there isn’t enough refrigerant in the system, the typical culprit is a leak. Use a UV A/C leak detector kit to check for leaks, including in the condenser and evaporator.

Next, use a manifold gauge to check the high and low side pressures in the system. Are they set within the recommended ranges provided in your owner’s/repair manual? Also, check the following for a tight and secure fit:

  • Front seal of compressor
  • All system fittings
  • Hose manifolds on compressor
  • All system hose crimps
  • Schrader valves
  • O-rings found on compressor pressure switches

Important note about replacing an A/C compressor

If you need to replace your A/C compressor, you'll also need to replace your accumulator and/or dryer and expansion device. You'll also want to conduct a full flush of the system for optimal performance. (Here's how to do a radiator flush.) Some vehicles require a replacement of the condenser to eliminate all debris from the A/C system.

A/C recharging

The EPA provides detailed information about the process and regulations. You can read them in full or use the summary we’ve provided below.

When recharging, there are two main options:

  1. Top off with refrigerant
  2. Empty/evacuate the system and recharge/refill the system

Although each can be effective, they are both temporary fixes if any A/C leaks still exist. And, if you have an older vehicle, what’s leaking is CFC-12 (Freon), an expensive refrigerant that is no longer manufactured in the United States because of concerns about the ozone layer. The cost of replacing CFC-12 will make it more economical, in most cases, to fix any leaks first.

Top-off versus evacuation and recharge

A top-off is cheaper, faster and simpler. However, any impurities in the refrigerant remain unless you choose the recharge process, which involves:

  • Removing any remaining refrigerant
  • Purifying the refrigerant using recycling equipment, recharging it into the vehicle and then topping if off, as necessary

Plus, the recharging allows you to be more precise. When topping off refrigerant, you can determine the optimal amount (say, 2.2 pounds) by looking in your owner’s manual. However, there is no precise way to know how much refrigerant is currently in a vehicle, making topping off an estimate at best. If the A/C system is accidentally overcharged, newer cars usually have a feature that causes the system to shut down in hot weather. With a recharge, you can be precise.

How to find a refrigerant leak

If only a small amount of refrigerant appears to be left, you'll need to add up to a few ounces. If the refrigerant has less pressure than 50 pounds per square inch, the EPA says more refrigerant is needed. (Note that at least 1 to 1.5 pounds of refrigerant is needed to test cooling capabilities.) The EPA recommends the use of an electronic leak detector that is Society of Automotive Engineers (SAE) J1627 certified.

It's possible to have pinpoint-sized leaks that are very difficult to find, even with the best equipment. These tiny leaks cause slow leakage but the A/C system may seem to lose its cooling capabilities virtually all at once. If that's the case, it’s likely that your vehicle has a system that shuts off once refrigerant drops below a certain level.

The EPA doesn't require that refrigerant be removed and cleaned before car air conditioning recharging takes place. To get more information, you can call them at 800-296-1996. The EPA also does not require that leak repairs be done before refrigerant is added, although states and/or localities can require this so it's good to check.

State-level agencies

Here are listings of state-level environmental agencies in alphabetical order. You can search the appropriate agency to find information for your state and/or contact them to ask them a specific question. Another useful tool is the Gateway to State Resource Locators, where you can narrow down your questions by broad type and then enter your zip code and further filter down the type of information you need.

Streamlined option

If you decide to just add refrigerant, A/C Pro is a solution to consider. It contains a sealant that helps stop leaks on hoses, gaskets and o-rings.

Here are the basic steps to use it correctly:

  • Locate the low-pressure connection point
  • Use the A/C Pro gauge to measure the system’s pressure
  • If low, refill by pulling the trigger on the product’s nozzle and monitor pressure via the pressure gauge device, making sure that you don’t overfill

Troubleshooting your vehicle's A/C? Share your tips and stories for other readers.

Last updated July 11, 2017

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