How to Troubleshoot the A/C in Vehicles

by Contributing Writer; Updated June 12, 2017

Keep the A/C system in your Vehicles up and running through regular troubleshooting. A trip to the shop can be an expensive proposition, so arriving armed with a few tips can help save you money. Usually, the problems are fairly easy to remedy, whether it be a faulty compressor or a blown fuse. Before taking your Vehicles to a mechanic, there are a few basic troubleshooting steps you can run through on your own.

Under The Hood:

 How to Troubleshoot the A/C in a Mercedes E320

Check to see that the AC controls are operating correctly. Start the engine and turn on the fan and air conditioner. If the controls are difficult to move or loose, have them replaced. If the fan does not switch on, a fuse might have blown or the fan motor could have blown. Replace the fan.

Inspect the fuse box for blown fuses. The fuse box in a Mercedes E320 is on the end of the driver's side dashboard. Open the door to access the panel. Consult the diagram on the inside of the fuse box cover to identify the fuse that corresponds to the AC system. If the fuse is damaged, replace it with another of the same amperage rating.

Ensure that the valve control is operating correctly by checking the two AC/heater hoses under the hood while the engine is running. The hoses protrude from the firewall. The firewall divides the engine and passenger compartments.The hoses are similar to the thickness of a garden hose. Place your hand on the two hoses. Both should be warm to the touch. However, one should be noticeably cooler than the other. If not, this could mean that the valve control needs to be replaced. Have a qualified mechanic investigate further.

Turn up the air conditioner to its highest setting with the engine running. Check under the hood to see whether the magnetic clutch connected to the AC compressor engages. If you do not see or hear the clutch turn over, the system might be low on refrigerant. Have a mechanic refill the system. An excessively noisy compressor could mean that it is close to failing.

Check all the AC hoses for leaks. If you notice a green, oily residue on them, they could be damaged and may need to be replaced.

Use the AC compression test gauge (with the engine off) to check for sufficient pressure in the AC system. The test gauge has red and blue hoses attached to red and blue monitors to calculate the pressure. Remove the black caps from the service ports on the E320's AC unit. Screw the blue hose to the low-side service port and the red hose to the high-side port. Check the pressure readings on the monitors. If the reading is not between 50 psi and 80 psi, have a qualified mechanic investigate further as this could mean there is a leak in the system.

Items you will need

  • AC compression test gauge

 How to Troubleshoot the AC on a 1996 Chevy S10 2.2 Liter

Open the hood on your S10.

Find the AC compressor in front of the engine. The AC compressor has a belt attached to the engine so that it turns when running.

Ask your friend to start the engine while you look and listen to the engine. Have your friend turn on the AC. Listen for the car engine's RPMs to change. A working AC compressor will make a clicking sound when it turns on and will change the RPM of the engine because of the load of power. If you do not notice a change in the engine RPM and no clicking sound, then check the electrical connections to the compressor. If you are working on an AC system where the belt has been removed from the AC compressor, then make sure that the AC compressor is not frozen. You can turn the pulley on the AC compressor to make sure it moves. If it does not move, then you need a new compressor before moving on.

Find the AC inlet filler located on one of the AC lines entering the AC compressor. Sometimes there is a protective black cap that you can turn counterclockwise to remove.

Open your UV kit. In it you will find special Freon, sealant, UV glasses and UV light.

Press the Freon can onto the inlet connection and squeeze the trigger to fill the AC system.

Drive the car for a while with the AC on.

Park the vehicle and open the hood again. Put on your glasses and shine the UV light all around the AC lines and compressor. Try to see if you can find a leak in the system. You will be able to see the leak with the special glasses and light. If there is a major leak, then you will need to replace that part. If it is a pinhole leak, then proceed to the next step.

Press the can of sealer over the inlet connection and pull the trigger. Let the can fill the AC system. This sealant should stop a pinhole leak and get your AC system blowing cool air again.

Items you will need

  • Ignition key

  • UV leak and sealer kit

 How to Troubleshoot the AC in a 1998 GMC 1500

Turn on your truck and turn on the air conditioner. Then open the hood and look at the fan near the front of your engine compartment that blows air over your compressor. If this fan is off, it may cause your A/C to perform badly when your truck is not moving and will need replacing.

Touch the air conditioning system's low pressure line. This will be the larger line coming out of your truck's compressor. If this line is not very cold after you have left your A/C on for a few minutes, then the pressure in your lines may be too low.

Connect a set of A/C pressure gauges to your air conditioning system. This connects to the service ports that are clearly visible on both the low and high pressure lines of the truck's A/C system. Connect it to the low pressure side and take a reading. On a 70-degree day, the pressure for your GMC truck should be at 45 PSI. If the pressure is too low, the system needs more refrigerant. Your owner's manual will have more information on the recommended pressure of your system.

Turn off your A/C for a minute, and then have someone else turn it on as you stand over the engine and listen to the compressor. Have the person in the car turn on the A/C and listen for the compressor to start up; if it does not switch on, your compressor is broken and may need replacing.

Check to see if there are any leaks in the A/C hoses. You can do this by either purchasing a leak detection kit (which will color the refrigerant and provide you with a light that will help reveal where refrigerant is leaking from) or by rubbing soapy water on the pipes and checking to see if the water will bubble. If so, there is a leak and the hose will need to be replaced. This is most likely the problem if your system slowly gets warmer after you have refilled it with refrigerant.

Items you will need

  • A/C gauges

 How to Troubleshoot the AC in a Dodge Caravan

Turn on the A/C controls (with the motor running) on the vehicle dashboard to test for any switches that may be loose or damaged. Ensure that the A/C is turned on as well as the electric fan.

Start the engine and turn the A/C controls to the highest setting. Listen under the hood for the magnetic clutch attached to the compressor to turn over. You will be able to both hear and see the clutch kick on. The system may be low on refrigerant if the magnetic clutch does not work. There could also be a leak in the compressor itself.

Inspect all the hoses related to the A/C system for kinks or leaks. If you notice oily residue on the hoses, or any A/C component, you may need to have those parts replaced. Ensure that the drive belt is securely connected to the compressor. If the compressor is excessively noisy, it may be time to have it replaced.

Check the fuses. Open the driver's side door and remove the side panel next to the steering wheel to access the fuse box. Look at the instructions on the inside of the fuse panel to locate the fuse corresponding to the A/C system. If the thin metal strip inside the glass fuse is broken, replace it with another of the exact same amperage rating.

Check the pressure in the A/C system. Turn off the engine and attach the air conditioner compression gauge to the system. A normal reading should be between 50 PSI (Pound Per Square Inch) and 80 PSI. If the pressure is lower than this, have a qualified mechanic investigate this further for you. The A/C gauge has color-coded hoses; the blue color-coded hose has a connection that fits on the low-side service port, and the red hose has a connection that fits onto the high-side.

Start the engine and open the hood. Locate the two hoses near the firewall (about the thickness of a garden hose) and check to see if there is a difference in heat. One should be slightly cooler than the other. If they are both hot to the touch, the problem may lie with the valve control. Have a mechanic check this over for you.

 How to Troubleshoot the AC in a Toyota Highlander

FUSES

Inspect the fuse box for any blown fuses. The fuse box in the Toyota Highlander is to the left of the instrument panel, behind the small storage compartment.

Pop the compartment out and read the schematic on the inside of the panel door for instructions on how to locate the fuse corresponding to the AC system.

Replace the fuse with another of the same amperage rating if the metal strip inside the fuse is broken.

AC Controls

Turn on the engine, the AC and the blower fan.

Check if the controls are functioning correctly. Replace the controls If they are loose or hard to move.

Listen for the fan to switch on. If the fan does not begin to spin, a fuse may have blown, or the fan may be faulty.

AC Pressure

Test for sufficient pressure in the AC system. To do this, remove the black caps from the low and high side service ports on the AC unit.

Screw the blue hose from the AC test gauge to the low-side service port and the red hose to the high-side service port.

Take a pressure reading. The pressure reading should be between 50 and 80 PSI. Have a qualified AC mechanic investigate further if the readings are out of this range. The AC compression test gauge will automatically take the reading and has a window that displays the result.

AC Compressor

Check under the hood to see if the magnetic clutch connected to the AC compressor engages. You will be able to see and hear the clutch turn over. If it does not, the system may be low on refrigerant. Have a mechanic refill the system. The AC compressor is to the right of the engine block and resembles the alternator with a drive belt attached to it.

Take the car to a mechanic for clutch repair. The clutch will need to be replaced if it is receiving voltage but still not engaging the compressor.

Take the car to a mechanic for a compresser shaft repair. If you notice leakage around the compressor shaft seal, it will need to be replaced.

AC Hoses

Start the engine and check the two AC hoses near the firewall. The AC hoses protrude from the firewall and are roughly the thickness of a regular garden hose. The firewall is the metal divider between the engine and passenger compartments.

Place your hand on the AC hoses. They should both be warm to the touch; however, one should be noticeably cooler than the other.

Replace the valve control if the two hoses are the same temperature. Have a qualified mechanic do this for you.

Items you will need

  • Air conditioner compression test gauge