Last spring when my wife bought her new used car, a 2000 Chevy Cavalier, the A/C appeared to be working just fine but with the onset of hot weather things changed. It started blowing cool air instead of the ice cold air that she was use to in my vehicles. I was unaware of this because she didn’t mention it to me and I seldom ever rode in her car. Being the independent type she took it to a well known tire shop that also did auto A/C work to have it checked out. They ended up recharging the system with R134 Freon and it cost me $100. When I saw that charge on my credit card statement I had to take several deep breathes before asking my wife why she didn’t bring the problem to me because I could have recharged the system for less than $25. Her explanation was believable for her because she’s the impulsive type, “I was driving by and saw the sign ‘no appointment necessary’ so I pulled in and had it done.” My point is if your car’s A/C isn’t getting cold enough for you; don’t spend $100 or more to have done what you can do yourself for $25 or less. Actually, servicing the A/C system is something that should be done every spring as part of getting your vehicle ready for the long, hot summer months ahead.
First things first
The first thing that you need to do is check to be sure that your car’s A/C system uses the new R134 refrigerant and not the older R12 refrigerant. You can find this information in your car’s owner’s manual or in your service manual. What’s that? You don’t have a service manual for your car? Having a service manual for each of your vehicles is as important for the DIY mechanic as having a copy of the NEC (National Electric Code) is for the DIY electrician. Even professional mechanics have a complete set of Chilton or Motor’s auto repair manuals to refer to because every vehicle is different and there is no way anyone can remember all their different specifications. For the DIY mechanic there are two excellent repair manuals available for around $20 each- the Haynes Repair Manual and the Chilton Repair manuals. If you want to go hi-tech with an online service manual like many pro shops do so their techs can access the manual by wireless laptop connection, Chilton offers an excellent service for the DIY mechanic at a very affordable price of $19.95 per year per vehicle. You can also try the service for free to see if it’s something you want to subscribe to. Here’s the link http://www.chiltondiy.com/.
If your vehicle was manufactured after 1994 the odds are that your vehicle has a R134 system. R134 is the environmentally friendly refrigerant that doesn’t require special equipment to handle safely. If you have an older vehicle with an R12 system you will need to take it to a professional to have it converted to use the R134 refrigerant. You will have to bite the bullet and pay to have it done because unless you are certified by the EPA (Environmental Protection Agency) to work with refrigerants and have some very expensive equipment i.e. Freon recycling equipment that pumps out the old refrigerant into a recycling container without allowing it to escape into the atmosphere, you can’t do the job yourself. Actually you can’t even buy the older refrigerants anymore unless you are certified by and have a license from the EPA. From this point on I will assume that you have a R134 system and are ready to service it.
The auto A/C system-How it works
The basic auto A/C system consists of several major components-the evaporator coil, the condenser coil, the compressor, the expansion vale or orifice tube, accumulator, receiver/drier, pressure regulating device and the receiver.
· The compressor is considered to be the heart of the air conditioning system. It’s a belt driven unit that divides the system into a high pressure side, the discharge side and a low pressure side the suction side. The compressor is basically a pump that draws gas from the evaporator coil and compresses it before discharging it into the high pressure side of the system. Depending on the system design the gas is sometime sucked from the evaporator coil through an accumulator.
· An accumulator is basically a storage tank for liquid refrigerant and is connected directly to the suction side of the evaporator. Accumulators are used on systems that employ orifice tube to meter the refrigerant into the evaporator on the high pressure side. The purpose of the accumulator is twofold; it not only stores excess liquid refrigerant it isolates the compressor from the liquid refrigerant. Liquid refrigerant, if it was to enter the compressor would do serious damage to the compressor. The accumulator also acts similar to the drier by removing moisture and debris from the refrigerant before it enters the compressor. The accumulator should always be replaced anytime the A/C system is opened up for major repair but that type servicing is beyond this tutorial but I may do a series on major auto A/C repairs in the future if there’s interest.
· The evaporator is located in the passenger compartment as part of the heating/cooling system. The evaporator fan draws the warm cabin air through the evaporator where the heat is absorbed by the liquid refrigerant causing it to boil and change its state from liquid to gas. Refrigerants boil at a very low temperature which gives them the ability to absorb great amounts of heat from the air passing through the evaporator coil. The ideal operating temperature for the evaporator is 32°F or 0°C. The evaporator also serves as a dehumidifier by removing excess moisture from the air which accounts for the water you see dripping from under your car on really hot days. Evaporators have a tendency to become clogged with dirt so they need to be cleaned routinely as part of getting your vehicle ready for summer. If the evaporator runs colder it can freeze up and this will cause the A/C to stop producing cold air. If you’re A/C isn’t working properly it’s a good idea to check the evaporator before running out to buy a recharging kit. If there is an ice build up on the evaporator it’s a sign that there’s a problem with the pressure regulating device which is either an orifice tube or an expansion valve. Servicing the evaporator comes under major repairs and will be covered in a future factoid.
· Orifice tubes are the most common pressure regulating devices and commonly found on GM and Ford products. It’s not uncommon for these tiny orifice tubes to become clogged with debris and cause the system to stop working. Orifice tubes themselves are relatively inexpensive, costing $3 to $5 but replacing them is labor intensive and beyond this factoid.
· Thermal expansion valves are another common pressure regulating device commonly found on foreign imports and on aftermarket systems. There are many variations in thermal expansion valve design including Chrysler’s “H-Block” design. Thermal expansion valves are even more problem prone than orifice tubes because they have tiny, moving parts which are prone to sticking.
· Receiver-driers are located on the high pressure side of systems employing thermal expansion valves because they require liquid refrigerant to work properly. The receiver-drier primary function is to separate the liquid refrigerant from the gaseous refrigerant. The receiver-drier’s secondary function is to capture moisture and other impurities and keep them from entering the thermal expansion valve.
· The condenser serves the same purpose for the A/C system that the radiator serves for the engine’s cooling system; it dissipates heat to the surrounding air. As a rule these condensers are located in front of the radiator but, on some vehicles, because of space constraints, it may be located elsewhere. No matter where it’s located air must be able to flow through it for the system to work so make sure you clean of obstructions on a regular basis.
Okay, now that you know a little bit about how the system works we are ready to learn how to recharge a system.
What you will need
There are a couple of routes you can go here-the professional route and the amateur route. If you have a lot of vehicles or if you want to offer the service to friends and neighbors you may want to go the pro route and buy a set of manifold gauges and a tank of R134 but it’s also a very expensive route to take. If you only have one or two vehicles I suggest buying the DIY all-in-one recharging kits that are available at any auto parts supplier as well as at many general merchandise stores like Wal-Marts, Sear, etc. The all-in-one kits come with everything you need-R134 refrigerant, pressure gauge, valve adapters, etc and they only cost around $25 per kit.
Preparing the kit
· A WORD OF WARNING: Refrigerants under pressure are extremely cold and can cause frost bite and burns to the skin very quickly as well as blind you if you get it in the eyes so wear protective goggles and gloves whenever you are working with refrigerants
· Each kit comes with everything that you will need. Before you assemble the kit, and this is very important, back the knob on the tang gauge all the way out by turning it counterclockwise. This is important because the valve contains a needle designed to pierce the top of the refrigerant container and you don’t want to pierce the container until everything is hooked up and you’re ready to charge the system.
· After screwing the hose to the gauge, you need to calibrate the gauge for the ambient temperature. Calibrating the gauge is simply a matter of turning the calibration ring until it matches the ambient temperature marks on the face of the dial.
· You will be charging your system from the low pressure side so your next step is to locate the low pressure port. Your service manual will tell you where this port is located but each port are covered with a cap marked “H” for the high pressure port and “L” for the low pressure port.
· Automotive A/C compressors like those in refrigerators and freezers are delicate contraptions. Any debris entering them can cause serious damage to their sensitive components so make sure that you clean the area around the low pressure port before you remove the port cap. This may seem silly to you but one grain of dirt can destroy a compressor
· Now, with the port cleaned turn the knob on the valve completely clockwise sealing the gauge off then attach the hose to the low pressure port by pulling the sleeve back and slipping the connector over the port before releasing the sleeve to lock it in place
· With the hose firmly attached to the low pressure port, start the engine and set the A/C controls to “high”. Allow the engine to idle for a few minutes giving the pressure an opportunity to equalize between the high and low sides of the system. Note how much pressure the system is registering.
· Shut the engine off and disconnect the hose from the port. Turn the valve completely counter clockwise to retract the piercing needle and then screw the valve/gauge assembly onto the refrigerant container. With the valve assembly tightly screwed onto the can turn the knob fully clockwise piercing the can. You will actually be able to hear it when the piercing takes place
· Reattach the hose to the low pressure port. Start the engine once again and set the system to high. After allowing the pressures to equalize slowly open the valve allowing the refrigerant to enter the system. As the refrigerant flows into the system rotate the can slowly assuring an even supply of refrigerant to the valve. As the pressure slowly builds up watch the temperature mark that you calibrated for. When the gauge reaches this point your system is fully charged. Most all-in-one kits come with pretty detailed instruction on the actual recharging process. Read them carefully.
· Once your system is fully charged, close the valve and recheck the pressure. If the reading is still low add more refrigerant. If you are only off by a couple of pounds don’t worry about it, it’s not that critical. When you are satisfied with the pressure reading shut off the engine, disconnect the hose and replace the port cap to keep the dirt out.
· Save the valve, gauge and hose even if the can is empty because it can be reused. The next time you want to check a system or recharge one all you will have buy is the R134 and that will save some money.
