Expansion Valve

Another common refrigerant regulator is the thermal expansion valve, or TXV. Commonly used on import and aftermarket systems. This type of valve can sense both temperature and pressure, and is very efficient at regulating refrigerant flow to the evaporator. Several variations of this valve are commonly found. Another example of a thermal expansion valve is Chrysler's "H block" type. This type of valve is usually located at the firewall, between the evaporator inlet and outlet tubes and the liquid and suction lines. These types of valves, although efficient, have some disadvantages over orifice tube systems. Like orifice tubes these valves can become clogged with debris, but also have small moving parts that may stick and malfunction due to corrosion.

Orifice Tube

The orifice tube, probably the most commonly used, can be found in most GM and Ford models. It is located in the inlet tube of the evaporator, or in the liquid line, somewhere between the outlet of the condenser and the inlet of the evaporator. This point can be found in a properly functioning system by locating the area between the outlet of the condenser and the inlet of the evaporator that suddenly makes the change from hot to cold. You should then see small dimples placed in the line that keep the orifice tube from moving. Most of the orifice tubes in use today measure approximately three inches in length and consist of a small brass tube, surrounded by plastic, and covered with a filter screen at each end. It is not uncommon for these tubes to become clogged with small debris. While inexpensive, usually between three to five dollars, the labor to replace one involves recovering the refrigerant, opening the system up, replacing the orifice tube, evacuating and then recharging. With this in mind, it might make sense to install a larger pre filter in front of the orifice tube to minimize the risk of of this problem reoccurring. Some Ford models have a permanently affixed orifice tube in the liquid line. These can be cut out and replaced with a combination filter/orifice assembly.

Retofit Procedure

1. Evacuate the R-12, if there is any left in the system. By law, this must be done without venting (releasing the gas into the atmosphere) by a certified mechanic using approved R-12 Recovery equipment. Many installers will do this without charge, because the R-12 they recover from your system is valuable
	2. Attach Adaptor to the low-pressure port: The low-pressure port usually has a blue or black dust cap and is located on the larger diameter tubing that runs between the evaporator (in the dashboard) and the compressor (see FAQ, "How do I find the low-pressure port?"). Remove the dust cap . Attach the adapter to the low-pressure port.
	3. Charge the System & Measure Pressure: Assemble the hose and refrigerant can. Be sure the engine is operating and the A/C is set to maximum cooling. Connect the hose to the low-pressure port and preceed to charge the system. Measure the system pressure at any time by closing the can valve. Refer to the pressure gauge chart for refrigerant level and stop charging when you reach proper pressure.
	4. Attach Label: Confirm proper pressure, disconnect charging hose, reattach blue dust cap and attach retrofit label

Accumulator

Accumulators are used on systems that accommodate an orifice tube to meter refrigerants into the evaporator. It is connected directly to the evaporator outlet and stores excess liquid refrigerant. Introduction of liquid refrigerant into a compressor can do serious damage. Compressors are designed to compress gas not liquid. The chief role of the accumulator is to isolate the compressor from any damaging liquid refrigerant. Accumulators, like receiver-driers, also remove debris and moisture from a system. It is a good idea to replace the accumulator each time the system is opened up for major repair and anytime moisture and/or debris is of concern. Moisture is enemy number one for your A/C system. Moisture in a system mixes with refrigerant and forms a corrosive acid. When in doubt, it may be to your advantage to change the Accumulator or receiver in your system

Receiver-Drier

The receiver-drier is used on the high side of systems that use a thermal expansion valve. This type of metering valve requires liquid refrigerant. To ensure that the valve gets liquid refrigerant, a receiver is used. The primary function of the receiver-drier is to separate gas and liquid. The secondary purpose is to remove moisture and filter out dirt. The receiver-drier usually has a sight glass in the top. This sight glass is often used to charge the system. Under normal operating conditions, vapor bubbles should not be visible in the sight glass. The use of the sight glass to charge the system is not recommended in R-134a systems as cloudiness and oil that has separated from the refrigerant can be mistaken for bubbles. This type of mistake can lead to a dangerous overcharged condition. There are variations of receiver-driers and several different desiccant materials are in use. Some of the moisture removing desiccants found within are not compatible with R-134a. The desiccant type is usually identified on a sticker that is affixed to the receiver-drier. Newer receiver-driers use desiccant type XH-7 and are compatible with both R-12 and R-134a refrigerants.

A/C Recharging Method

Push-Button Dispensing

With Measure & Charge (MAC-134) and EZ Charge (SD-134), dispensing refrigerant is as simple as pressing a button. You just connect the hose to the low-pressure port, press the button on the can to fill (to "charge") and release to stop. With Measure & Charge, releasing the button will automatically give you a pressure measurement on the in-line gauge (which is re-usable). Both let you store unused refrigerant for later. Both contain the appropriate proportions of refrigerant and oil, as well as System-Safe leak sealer. See full instructions on this site or on the can.

Trigger Dispensing

With the Quick Charge charging gun (QC-1CS and QCK-2CS), you simply connect the hose to the low-pressure port, screw a can of refrigerant into the Quick Charge, squeeze the trigger to dispense and release to stop. Quick Charge will automatically give you a pressure reading on the built-in gauge. Quick Charge is completely re-usable. See full instructions on this site or on the package.

Direct Charge Dispensing

With High Mileage Top-Off (HMT-1DC), you simply press the direct charge fitting onto the low-pressure port to fill 6oz. of refrigerant & oil (in the proper proportion). Great when all you need is a small amount of refrigerant to top off your system. We recommend using our EZ Gauge (GEZ-1) to measure pressure before and after charging to ensure proper pressure for peak cooling. See full instructions on this site or on the can.

Screw-in Can Tap Dispensing

Several of our recharging kits use the traditional method of dispensing, tapping a can. These kits are models RKR-7, RKR-5, RGM-134, GBM-134, and MB-134. This method involves screwing a can tap with hose onto a can of refrigerant, partly unscrewing to dispense, and screwing in again to stop. With the RKR-7, RGM-134 and GBM-134, you can check pressure with the in-line gauge. The RKR-7 and RKR-5 can be used in two ways: to either retrofit (convert) an A/C system using R-12 refrigerant to a system that can use R-134a refrigerant, or to recharge a system that already uses R-134a. See full instructions on this site or on the package.

Refrigerants

Regardless of the type, all air conditioning systems function according to a basic law of physics that states ‘a fluid absorbs heat as it changes from a liquid to a gas, and a vapor releases heat as it changes from a gas to a liquid.’ In an A/C system, refrigerant is the transfer medium used to absorb the heat inside the passenger compartment and release it to the outside air. Refrigerant is a tasteless, odorless gas with an ability to change state rapidly within a specific temperature range. It is also oil soluble and non-corrosive. While there are scores of refrigerants on the market, there are only two types approved by vehicle manufacturers: R-12 and R-134a.

R-12, commonly referred to as Freon, has long been used as the refrigerant in all automotive A/C systems. However, R-12 contains chlorine, which is the primary cause of ozone layer damage. Consequently, legislation was passed calling for a halt in R-12 production by 1996. Long before the phase-out of R-12 began however, the automotive industry conducted extensive research and development to find an environmentally friendly alternative. They ultimately selected R-134a as the new refrigerant, and began using it in vehicles as early as 1992.

R-134a is similar to R-12, in that it absorbs, transfers, and releases heat efficiently. It is also non-flammable, and mixes well with oil, just like R-12. However, R-134a does have some unique characteristics.

• R-134a requires a special synthetic lubricant since it does not mix with mineral oil (standard R-12 lubricant).
• R-134a operates at higher discharge pressures than R-12. Therefore, systems using R-134a may not cool as well as R-12 when the vehicle is idling for extended periods (e.g. heavy traffic).
• R-134a and R-12 cannot be mixed, which is why separate equipment is needed to service vehicles using either refrigerant.

Depending on the vehicle, refrigerant capacity can range anywhere from about 28 ounces (1.75 lbs.) to as much as 64 ounces (4.00 lbs.) or more. To avoid an improper charge, always consult the manufacturer's specifications for refrigerant capacity. An improper charge will cause reduced system performance, and may even result in system damage.

Refrigerant Oil

In order to function properly, an A/C system requires the appropriate type and amount of oil. In addition to lubricating the compressor, refrigerant oil also maintains the operation of the expansion valve on systems so equipped. Since the oil is transported through the system by the refrigerant, it has to be compatible with the type of refrigerant being used. Mineral oil is the lubricant used for all R-12 systems, while R-134a systems use synthetic oils such as PAG (polyalkylene glycol) and POE (polyolester).