Part number 8900 supplied without service hoses.
Part number 8904 supplied with 1-36" Red, 1-36" Blue, 1-60" Yellow service hoses.

The manifold gauge set is the most important tool used to service air conditioning systems. The manifold set is used to determine the system's high and low side gauge pressures, the correct refrigerant charge, system diagnosis and operating efficiency. It is designed to read both the high and low sides at the same time, because pressures must be compare to determine system operation. All gauges are explained in detail in the following pages.

Low side Gauge: This gauge, is used to measure low side pressure and vacuum readings at service ports. It reads from 0 to 150 psi (pressure scale) in a clockwise direction, and from 0 to 30 inches of Mercury (vacuum scale) in a counterclockwise direction

A test hose (normally blue) connected to the fitting directly under the low side gauge is used to connect the low side of the test manifold into the low side of the system. A similar connection (normally red) is used on the high side. The center fitting on the manifold is used to connect a service hose to charge or evacuate the system. The service hose is normally a neutral color such as Yellow or White.

1.    Before starting turn both control valves on the Manifold Gauge Set to the closed position.
2.    Attach one hose (red) to the high pressure gauge fitting on the Manifold Gauge Set or charging station. 
       Connect a second hose (blue) to the low pressure gauge. A third hose  (yellow) is the auxiliary hose.
3.    After connecting the hoses to the gauges move the service caps that protect the fittings on the air
       conditioning system and connect each hose to the correct fitting.
       The high pressure gauge hose (red) goes to the fitting in the high pressure portion of the system.
      The low pressure gauge hose (blue) goes to the fitting in the low pressure portion of 
       the system.  The second low pressure gauge hose (yellow) is the auxiliary hose.
4.    Purge all hoses of air (to prevent incorrect gauge readings and system contamination) by
       opening the low pressure gauge shut off valve on the manifold set slightly for a second, then
       close the valve. Repeat the process on the high pressure gauge. The hose can now be purge
       by loosening the fitting at the hose slightly until you can detect the air escaping.
       Retighten the fittings before actual operation.
 

Pressure gauge readings are the primary means of locating and identifying malfunctions in the refrigeration system. Gauge readings alone, however may not provide enough information to pinpoint a problem since different types of problems frequently produce similar readings. As a result, problems can best be pinpointed by combining the information provided by the gauges with other clues provided by other signals being given off the system.
When taking gauge readings remember that the readings will be affected by changes in temperature, humidity and altitude. Both high and low pressure gauges readings will increase as the ambient temperature and humidity increase. Increases in the altitude have the opposite effect. A system tested at sea level will produce higher readings than it would when tested under exactly the same conditions at higher altitude

When trying to diagnose a problem look for gauge readings tat differ greatly from those consider "Normal" and disregard those that are slightly higher or lower than "normal".
 
 

Normal Range if ambient temperature is	Normal Low side Gauge reading is	High Side gauge reading is
70 F 75 F 80 F 85 F 90 F 100 F 110 F 115 F 120 F	12 P.S.I. 14 PS.I. 16 PS.I. 18 PS.I. 20 PS.I. 24 PS.I. 26 PS.I. 28 PS.I. 30 PS.I.	115-135 130-150 150-170 165-185 175-195 210-230 230-250 250-270 265-285

CAUTION: Always connect hoses to the manifold gauge set before connecting hose to service valves in the system to prevent refrigerant from escaping from unmated fittings and to prevent air from entering an evacuated system.  Never open the high pressure hand valve when the A/C System is operating.  Change with gas only, not liquid. (CONSULT OEM SPECIFICATIONS)

After all connections have been made the refrigerant can be added by the Low Side Method on most systems. (consult OEM specifications.)

    1. Make certain that the dispensing valve on the refrigerant source is in the closed position.
    2. Make certain that both the high pressure and the low pressure valve on the manifold gauge set are in their
        closed positions.  If Hand Shut-Off Valve are used in the system they can be left  in the open position.
    3. Turn on vehicle engine and set idle speed at 1500 rpm.  A large electric fan can be located in front of the 
        vehicle to insure a steady flow of fresh air to the air conditioner condenser and radiator. (Fan optional)
    4. Turn on air conditioner.  Set controls at maximum cooling and high fan speed.  Open vehicle doors and
         windows to permit good air flow though interior of vehicle.
    5. When ready to begin adding refrigerant (with the system running) open the control valve on the low
         pressure gauge side of the Manifold Gauge Set.
    6. Open the dispensing valve on the refrigerant source.  Keep the refrigerant source upright at all times so
         that refrigerant can only enter the hose as gas.  Allow the gas to flow into the system until the desired
         amount has been added or until the source container is empty.  Refrigerant will continue to flow as gas 
         as long as the pressure in the can is greater then the pressure in the system.  Getting all possible
         refrigerant into the system may take several minutes.
         NOTE: When changing refrigerant source the low pressure valve on the manifold gauge must be returned
         to its closed position.
    7. When charging function is complete disconnect all hoses.  In cases where Hand Shut-Off Valves are used
         turn valves in the closed position before disconnecting hoses.
    8. To evacuate the A/C System connect the yellow hose to the vacuum pump and open both hand valves on
        the gauge set them turn on the vacuum pump.  Operate the vacuum pump for at least 30 minutes. 
        (Consult OEM Specifications)