Determine the type of system to be charged. In the US only equipment that has been converted to or came from the factory with 134a can be legally charged with 134 replacement refrigerants. In Canada and most other countries our refrigerants can be installed with no retrofit or conversions needed for either system type.
After determining the system type, make sure you have the proper equipment to do the job. If it’s a 134 system it will have the larger caps on the service ports. 134 systems use a larger quick disconnect coupler for the high side than the low. Always charge into the smaller one. That is the suction or low-pressure coupler. Equipment needed can be a simple can tap and hose combination to a complete set of manifold gauges and charging hoses used by service technicians. Smaller single gauge hoses can be used to monitor low side or suction pressure while charging. This works well for the guys that just need to add a can once or twice a year but for larger users, the full gauge sets are best, especially if using from a refrigerant cylinder.
Connect charging hoses to the proper ports and see if any pressure is seen on the gauge. If none or very little, it should be all right to start the engine and turn on the AC. If the compressor clutch engages and runs intermittently at very short cycles, it is a sign that the system is low on refrigerant. With a can attached to the hose, pierce the top of can by turning in the knob or thumb screw clockwise all the way, them back it out some until the gauge shows an increase in pressure. That means the refrigerant is being released from the can and the hose should become cold as the contents are drawn into the system. It is best to invert the can during this process. The compressor should run at longer intervals as the product is added or if the compressor wasn’t running at all, most of the time the pressure from the can will allow the low pressure switch that protects the compressor from running dry to close and the compressor may start cycling by itself. If this doesn’t occur then bypassing the switch with a jumper wire may be necessary.
Continue adding until the can goes empty or until the pressure reaches the desired level. Usually when the compressor stays on without cycling you should be near the proper level. When using a single gauge or gauge set, the suction pressure should be read only when the compressor is running or cycling and with the supply shut or the can empty. Other wise you will be reading can pressure and not system pressure. The exact suction pressure or low side pressure will vary with the outside air temperature. Usually charging works best at temperatures above 70 degrees F. Also the type of unit varies. Farm and heavy equipment will read lower pressures than cars and pickups. Usually most tractors and combines will be fully charged when the low side pressure reads in the low to mid twenties at about 1/3 throttle. When engine is fully advanced those pressures on the low side will drop some possibly into the low to mid teens. This in normal. The high side pressure can be read at the same time using a full gauge set. The high will usually run in the area of 150 to 200 when at full throttle again depending on the outside temperature. Autos can run with low pressures in the 30 to 45 area and the high can exceed 200 quite easily while sitting but usually when driving the pressure will drop.
When using our Industrial 12a, the pressures will run almost identical to the old R12 refrigerant. Our “Regular” refrigerant such as the product in the aerosol cans and the “Refrigerant with Dye” will operate at pressures slightly lower (about 10# to 12# less on the high side) than R12.
Remember, Do not overcharge. That only adds stress to all system components and will not make your system operate colder. Most systems hold a given amount of refrigerant when new. If the system is totally empty for service or some other reason, the proper amount needed can be determined by calculating the number of cans using the conversion on the label. When using from a cylinder, a refrigerant scale is best if doing a lot of recharging. They are extremely accurate and some can be pre-set to shut off the charge when the correct amount is drawn from the container. If this isn’t practical then go by the pressures until system is operation satisfactorily.
Remember too that sometimes there is something else wrong besides just being low on refrigerant. A good gauge set can help diagnose system problems if something else is wrong. Blockage can be determined and even poor expansion valve operation among other things.
All the necessary equipment needed to recharge is available in our equipment catalog on this site, all at the most reasonable prices anywhere.
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