米切尔-空调压力测试

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Condenser Temperature
The dial thermometer has been placed to measure the air temperature going to the condenser. At this 95o F temperature, the high side pressure should be between 210 and 290 psi.
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R-12 Service Ports
R-12 service ports use a flare fitting with external threads. The smaller high side port requires an adapter to connect to the service hose. The Schrader valve keeps these ports closed.
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Low side Service Port
This low side port is on the line connecting the orifice tube (at the condenser outlet) to the evaporator. It can be anywhere between the expansion device, orifice tube or TXV, and the compressor inlet.
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Static Pressure
R-134a should have a pressure of 79 psi at 75o F (24o C). The gauges should show the pressure that is related to the temperature of the refrigerant in the system. An odd or different pressure indicates a probable fault in the system.
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Connect Gauges
The low and high side hoses have been connected to the service ports (blue and red arrows). Both hand valves are closed, and the static pressure can be read on the gauges.
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A/C Service Units
This service unit has two pressure gauges and service hoses, high and low side. It also has the ability to recover and recycle refrigerant as well as evacuate and recharge a system. The control pad and display control the various operations.
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Gauge Sets
A portable gauge set has: •two gauges to read the high and low side pressures, •two hand valves to control the flow through the inner passages, and •three hoses to connect to the service ports and vacuum pump or refrigerant supply.
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Operating Pressure
The low side gauge reads a pressure of about 30 psi indicating that the actual evaporator temperature should be about 35o F. The high side gauge reads about 205 psi indicating the refrigerant in the condenser should be about 130o F.
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R-134a Service Ports
R-134a service ports are a quick-connect fitting with the high side port a larger diameter. These ports also use a Schrader valve to close the port and prevent refrigerant leakage.
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Start the System
•Make sure that the service hoses are routed so they will not contact the fan, drive belts, pulleys, or exhaust manifold. •Start the engine, and turn the system on: A/C at full cold with low blower speed (We want to see if the clutch will cycle). •Run the engine at a speed of about 1,000 to 1,500 rpm.
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Determine Condition
Are the pressures good; did they fall within the pressure ranges for proper operation? If so, the HVAC system should operate properly. If not, determine whether the high side and low side pressures were low, normal, or high. Record the pressures as they can help you determine what fault is in the A/C system. Low Side: Low, Normal, High, Actual pressure _____ High Side: Low, Normal, High, Actual pressure _____
A/C Pressure Test
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A/C Tests


Pressure Tests, show system high and low side operating pressures Temperature Checks, confirm proper refrigerant action, and Pressure-Temperature relationship
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Disconnecting Gauges
When you finish, shut off the system and the engine. Many technicians will disconnect the low side service hose immediately after shut down while the pressure is the lowest. They will disconnect the high side hose a little later, after the high side pressure drops. Be sure to replace the caps on the service ports.
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Pressure Change
When the compressor starts operating, the low side pressure should drop, and the high side pressure should increase.
Animation: Gauge Pressures
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Electronic Gauges
An electronic gauge can be used to read system pressures. It can also be used to measure temperature and vacuum as well as compute superheat and subcooling. Transducers are connected to the service ports and convert the pressures to electrical signals. This type of gauge is used for diagnosis only.
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High Side Service Port
This high side port is at the compressor discharge outlet. It can be anywhere between this point and the expansion device. Note that the cap has been removed from this port.
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Service Ports
Most systems will have a service port in both the high and low side portions of the system. Each port should have a cap to keep the internal valve clean and to serve as a refrigerant seal.
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Pressure Tests
Low side pressures (Blue lines) should relate to low evaporator temperatures, about 30 psi. High side pressures (Red & pink lines) should relate to ambient temperature at the condenser, about 150 to 250 psi.
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High Side Pressure
High side pressures for many vehicles is model specific; the best policy is to use the specifications for that particular vehicle. The pressure relates to the temperature and amount of air going through the condenser. Warmer air or restricted air flow produces higher pressures.
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Low Side Pressure
The low side pressure should drop until a point where the clutch cycles, a variable displacement compressor cuts back, or a suction throttling valve starts throttling. This depends on the type of A/C system. This pressure of 30 psi indicates an evaporator refrigerant temperature of 35o F (1o C) which should produce an air temperature of about 45o F (7o C).