How to Perform AC Pressure Test?

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The AC pressure testing is As follows :----

Pressure Testing

A pressure gauge set is used to measure pressures in the system. One of the gauges is for high side pressure and the other is for low side pressure.

A pressure gauge set is used to measure pressures in the system. Courtesy of Ford Motor Company.

The gauges and hoses are of a standard color code:

• Red is the high side.
• Blue is the low side.
• Yellow is for charging and discharging equipment.

This is the same color code that plumbing follows for hot and cold water. The gauges are connected to one manifold with another hose fitting for performing service procedures. Evacuation and recharging of the system can be done through this port.

Before connecting the gauges to the service ports, close the manifold hand valves and any valves on the service hoses at a refrigerant tank or vacuum pump. Be careful that the hoses do not hang in the fan or on an exhaust manifold. Then, connect the gauges.

Connect the gauges to the service ports. Courtesy of Ford Motor Company.

The low pressure gauge is a compound gauge. It reads in either low pressure or vacuum. This is because it is in the suction side of the system. There is a hand-operated valve that opens and closes the suction line to the service hose used to charge the system. The gauge is always open to the suction line and registers that side's pressure.

The high side gauge registers pressure only. The gauge usually reads to 500 psi. Most high side gauges have a small orifice in the inlet. This keeps the needle from fluctuating rapidly as the system pulses. Many gauges have a zero calibration adjustment screw on the gauge face also. Sometimes gauges have a scale to convert pressure readings to relative temperature.

The hand control valve for the high side opens and closes the line to the high pressure service hose, used for discharging the system. The gauge always measures pressure in the high pressure side.

With manual service valves, use a special wrench to mid-seat the valve by turning the stem one or two turns. It must be back-seated before removing the hoses. Modern service hoses have a check valve in the end of the line to prevent refrigerant from escaping when the line is disconnected. A small amount can still get out. When removing a hose from a connection, put a shop rag around it to prevent oil and refrigerant from spraying. Disconnecting the low side while the system is running results in the lowest pressure at that connection.

The pressure reading in the system when it is not operating is called the static pressure. This will be at least 50 psi if there is enough refrigerant in the system. High and low side pressures will be equal when there is no movement through the system.

When you start the engine and turn on the AC system, the low side pressure will drop and the high side will increase. Pressure on the low side will change according to the temperature in the evaporator. The high side will reflect the temperature of the liquid refrigerant leaving the condenser. The pressures will continue to change until the system stabilizes (reaches its normal operating temperature). The system pressures are stabilized when maximum high side pressure when the system cycles off does not change from cycle to cycle.

The pressures will vary with humidity because high humidity puts a higher load on the system. Adequate air flow over the condenser is also required. A portable fan might be necessary to blow additional air through the grill on a car with a belt driven fan. Expected low side pressures differ between expansion valve and orifice tube systems. Troubleshooting charts in manufacturers' service manuals will help pinpoint the causes of pressure problems. The following are rules of thumb for the pressure test:

• The higher the high side pressure, the more heat there is.
• The lower the low side pressure is, the lower the temperature will be at the outlet.
• High side pressure affects low side. When you squirt water on the condenser, the high and low pressures both drop at once.

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This details will help you.

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