[TxGreaseMonkey]

Wear safety goggles and gloves when working with refrigerant. Very important: Only add refrigerant to the low side port.


1. Fuse Testing. Test all under hood and under dash fuses with a test light or multi-meter.

2. Relay Testing. Verify that the compressor clutch relay and the condenser fan relay are operating properly.

3. Leak Testing. Look for obvious signs of refrigerant oil and dirt accumulation, especially around the compressor. With the A/C system on, apply Snoop or soap and water to fittings and look for bubbles. There are a host of more sophisticated dye injection kits, ultra-violet LED inspection lights, and sophisticated refrigerant sensors available to locate leaks. If it's more than just tightening a connector, the refrigerant will need to be recovered and the component replaced. Once the system is opened, it's best to replace the accumulator and orifice tube found on most GM and Ford models. Similarly, it's best to replace the receiver-drier and thermal expansion valve (TXV) found on most imports, when the system is opened. Replace O-rings on all new components and leaking connections, coating them with PAG oil. Afterwards, the system will need to be evacuated (vacuum pumped for 40 minutes at 28 in-Hg) and recharged. The static pressure test, below, will help assess whether there is a leak--it won't help you locate it, however.

4. Pressure Testing. A manifold gauge set (U.S. General, $40, Harbor Freight) is essential to troubleshooting and maintaining air conditioning systems. Never attempt to add refrigerant without using a manifold gauge set. It’s imperative to obtain information about what’s happening inside the system first. Without a manifold gauge set, you don’t know how much refrigerant, if any, that needs to be added. By using the proper equipment, you prevent overfilling the system and destroying the compressor, by monitoring the high and low system pressures. Here’s how to attach the hoses:

. Connect the low side (blue) hose to the low side port on the A/C unit.

. Connect the high side (red) hose to the high side port on the A/C unit.

. Connect the center service (yellow) hose to the refrigerant cylinder, while charging, or to the vacuum pump, while evacuating air and moisture.

• Static Pressure Test. An initial pressure reading indicates if the system has enough pressure to satisfy the low pressure switch and enable the compressor to operate. Most low pressure cut off switches turn the system off at approximately 20 psi. Compressors will not normally function until the pressure reaches 45 psi. Therefore, you need a static pressure of at least 45 psi, before the compressor will normally operate. Open both hand valves so that the gauges register the A/C system pressure. Static pressure is also used to determine if a system has enough pressure to begin leak testing (50 psi minimum).

• Low Side and High Side Pressure Test. Start the engine and allow it to reach normal operating temperature. Turn the A/C system on and set it to “max/high” output. With an engine speed of around 1,000 rpm, check the low side reading, which should be 25 to 35 psi. Next, check the high side reading, which should be about 200 to 350 psi. It’s best to consult a manual for the recommended pressures for your vehicle. On my 1993 Civic, for example, the low side pressure is 36 psi and the high side pressure is 320 psi. On my 2000 Ford Taurus (FFOT), depending upon the clutch cycle switch, the low side pressure is 22 to 45 psi, while the high side is 125 to 230 psi.

If the readings are lower than normal, close both hand valves to the manifold, attach a can of refrigerant to the yellow service hose, loosen the center hose at the manifold gauge set and allow a small amount of refrigerant to escape to purge air and moisture from the center hose, retighten the center hose connection, open the hand valve to the low side of the manifold, and add enough refrigerant to bring the readings up to the normal ranges. Warning: If the low side service port isn’t on the accumulator, keep the refrigerant container in an upright position, permitting charging with refrigerant vapor only. Afterwards, close the manifold gauge set low side hand valve and the refrigerant supply valve.

• Compressor Test. A bad compressor will normally show the inability to generate enough suction and pressure at idle speeds. If the engine speed needs to be increased substantially to bring pressures in range, it's a sign the compressor is weak. The typical complaint is, "It only cools when the engine is revved or when driving down the road." It's often simple. If we hook, for example, the gauges up and see 80 psi on the low and high sides and the compressor hub is spinning, the compressor is shot. It's not producing suction or pressure. We could add more refrigerant and nothing would change. Compressors must be able to pull a vacuum and create pressure.

• Final Performance Test. Place a thermometer in the far right air conditioning outlet, with the air conditioning controls set to their maximum cooling position. Adjust the blower speed to low and allow the system 5-minutes to stabilize. The thermometer should read 35 to 45 degrees F, at approximately 75 to 80 degrees F outside temperature. If you notice, after driving the vehicle for a while, that air stops coming out of the vents, the A/C clutch cycling switch may be bad. The cycling switch is supposed to control the evaporator core pressure at a point where the plate/fin surface temperature will be maintained slightly above freezing. Instead, it may be energizing the clutch too much and the system is icing up. In this situation, simply unscrew the old cycling switch from the Schrader valve-type fitting on the accumulator, coat the threads and O-ring with PAG oil, and install the proper cycling switch. It is not necessary to discharge the refrigerant system to remove the switch. The cycling switch's cut-on and cut-off pressures are readily available in manuals; therefore, its operation can be monitored by the manifold gauge set and you can tell whether its working properly or not.

[r.a.c]

When performance testing a air-con system,both hand valves are in what position?

[TxGreaseMonkey]

The manifold gauge set is not even connected to the A/C system, during performance testing.