The air-conditioning (A/C) system of a vehicle is a closed system for exchanging heat from the inside of the cabin to the outside. This is accomplished by circulating refrigerant gas though a circuit of tubes into two large surface areas that act as sinks either absorbing or giving off thermal energy.
Refrigerant gas is also known as Freon, a popular brand name for an older product. The refrigerant boils or evaporates into a gas as it absorbs the heat in the cabin via the evaporator located inside a fan or blower box. It then condenses or turns into a liquid state when it gives off that thermal energy into the surrounding air, in the condenser located in front of the radiator, which is ventilated by the auxiliary fans and the wind blast as the car moves forward.
The A/C’s efficiency thus depends on an accurate amount of this refrigerant gas inside the system, optimized for the size of the evaporator, the condenser, the tubes, and other ancillary components. Through an expansive closed system, the refrigerant gas makes its way from the cabin, out into the engine bay and back, passing through a maze of connectors and fittings as well as moving parts inside the compressor, all of which are sealed with rubber seals or O-rings. These could, in time, wear out and cause vacuum leaks in the system.
A small leak manifests as gradually warmer air from the A/C vents over a period of weeks to months. When the volume of refrigerant drops significantly, there won’t be enough refrigerant for efficient heat exchange to occur; the A/C won’t be blowing cold air out of the vents. As the refrigerant volume and pressure get lower, the compressor clutch won’t engage. Adding more Freon can temporarily bring it back to the recommended volume and pressure until the leak is found and mended.
Adding a sealer when refilling may help seal a small leak, but it will cause more problems down the line, like clogging up the expansion valve and drier. The sealer is meant to react with moisture in the system: It hardens as it contacts water to stop the leak, the same way it would plug up those parts.
The type of refrigerant used—commonly R-134a—and its volume by weight should be in the owner’s manual or in an information decal stuck on the engine bay. Older vehicles may still use the chlorofluorocarbon-containing, ozone-depleting R-12. For those systems, an A/C upgrade is the only fix, as R-12 is no longer available. Late-model cars will be using the new gas R-1234yf, which has a lower Global Warming Potential (GWP) rating than R-134a.
To add refrigerant, you’ll need the following: refrigerant recharge hose with gauge, the specified refrigerant gas, and a thermometer. Borrow a recharge hose from the A/C supply shop you purchase your refrigerant from. Gas costs about P500 per kilo, and in a small car, the air-conditioner’s total capacity is only 0.5kg. Larger vans may require 1.2-1.5kg. There are commercially available refrigerants in aerosol cans with a hose connector and gauge meant for topping up.
Precautions before proceeding: Refrigerant gas is hazardous when it comes in contact with the skin, and may cause blindness if sprayed into the eyes. Wear appropriate protective goggles and a long-sleeved shirt. If direct physical contact is made, wash the affected area with liberal amounts of cold water and avoid rubbing it. Frostbite can flake off skin when rubbed, and fingers can get stiff and brittle if not rewarmed early. Inhaling refrigerant gas directly can cause suffocation.
If that didn’t scare you enough, read the rest of the instructions.
You’ll want to see what you’re doing and avoid inhaling gas leaks if they occur.
Turn it all the way up to maximum coldness. Stick the thermometer on a vent and get a reading. If you put the back of your hand directly on the vents, it should be biting cold. If you have a thermometer in there, the temperature reading is going to be 18-21 degrees Celsius.
If the temperature is well above 21 degrees and the clutch is engaged, you may need to refill the refrigerant. If it is not engaged, it could mean the compressor is busted, or the clutch is not electrically activated, or the refrigerant level is too low. The next steps will determine which is the problem.
Find the low-pressure port—it will have a cap labeled L, or a black or dark-gray cap with no label. If you’re using a refill hose, it will only mate with the smaller, low-pressure port and won’t fit the larger, high-pressure one. Also, the low-pressure side of the system would be closer to the firewall as it exits the cabin, aft of the expansion valve. The high-pressure side is closer to the front of the vehicle where the condenser sits in front of the radiator.
A full-to-capacity A/C will read approximately 40psi when the clutch is on. If it’s less, it is undercharged. Over 50psi means it’s overcharged and the refrigerant won’t have room to expand inside the system, so it will also result in poor cooling as heat cannot be exchanged. If it’s overcharged, don’t vent the excess gas out into the atmosphere; recover it in an empty tank. If the clutch won’t hook up, check the fuses and electrical connections for the clutch.
If it’s undercharged, you can fill up with refrigerant gas only when the clutch is engaged and the system vacuum is on. Verify that the clutch is spinning with the compressor, then open up the tank tap, or pull the aerosol-can trigger, a few seconds at a time until the gauge reads 40psi. Draining an overcharged system into an empty tank with a vacuum inside it will be similar to refilling the system with a tank of gas.
It should now read 18 degrees Celsius. Verify that after reaching its lowest temperature, the clutch disengages and engages again as the vent temperature rises.
These steps should be pretty straightforward to follow. If your car’s A/C still doesn’t cool the cabin afterwards, then that might be another problem in itself—I suggest you take it to a specialist and have it checked.