Air Conditioning

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.

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


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.  Some vehicles require a replacement of the condenser to eliminate all debris from the A/C system.


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:

  • Top off with refrigerant
  • 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.


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.



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.