System Checking With the Manifold Gauge Set

System checking with the Manifold Gauge Set

Evacuating the Manifold Gauge Set
1. Attach the center (service) hose to a vacuum pump and start the pump. Open fully both high and low valves and allow the vacuum to remove air and moisture from the manifold set for at least five minutes.


CAUTION: It is imperative that the vacuum pump is not subjected to a positive pressure of any degree. Therefore the pump must be fitted with an isolation valve at the center (service hose) connection and this valve must be closed before the pump is switched oft. This operation replaces the 'purge' procedure used on previous systems. Observe the manufacturer's recommendation with regard to vacuum pump oil changes.


Turn the vacuum pump off and isolate it from the center service hose but do not open the hose to atmosphere.

Connecting the Manifold Gauge Set


CAUTION: Only use hoses with connectors which are dedicated to HFC 134A charge ports.


1. Attachment of the hose quick release connectors to the high and low side system ports is straightforward, provided that the high and low valves are closed and the system is NOT operational.


WARNING: UNDER NO CIRCUMSTANCES SHOULD THE CONNECTIONS BE MADE WITH THE SYSTEM IN OPERATION OR THE VALVES OPEN. SHOULD THE VALVES BE OPEN AND A VACUUM PUMP OR REFRIGERANT CONTAINER ATTACHED, AN EXPLOSION COULD OCCUR AS A RESULT OF HIGH PRESSURE REFRIGERANT BEING FORCED BACK INTO THE VACUUM PUMP OR CONTAINER.


Assessment of system operating efficiency and fault classification may be achieved by using the facilities on your Recovery/Recharging/Recycling station, follow the manufacturer's instructions implicitly and observe all safety considerations.

Stabilizing the System
1. Accurate test gauge data will only be attained if the system temperatures and pressures are stabilized.
Ensure that equipment and hoses cannot come into contact with engine moving parts or sources of heat.
It is recommended that a free standing air mover is placed in front of the vehicle to provide air flow through the condenser/cooling system.
Start the engine, allow it to attain normal working temperature and set at fast idle (typically 1200 to 1500 rpm).
Select full air conditioning performance.
With all temperatures and pressures stable, or displaying symptoms of faults; begin relevant test procedures.

Graph-High Side Pressure Against Ambient Temperature:

7. The 'Normal' condition is that which is relevant to the prevailing ambient temperature.

Graph-Low Side Pressure against Evaporator Temperature:

8. (To obtain lbf/in2 from bar, multiply the figure by 14.5)
Probable causes of faults may be found by comparing actual system pressures, registered on your manifold gauge set or recovery/recharge/recycle station, and the relevant pressure to temperature relationship graph. The following chart shows the interpretation that may be made by this difference.


NOTE: The A/CCM will disengage the compressor clutch should the evaporator temperature fall to 0 °C.


NOTE: Graphs are typical for HFC 134A


The 'Normal' condition is that which is relevant to the prevailing evaporator temperature.

System Pressure Fault Classification


1. NOTE: If erratic or unusual gauge movements occur, check the equipment against a known (calibrated) manifold gauge set.





This table should be used in conjunction with the graphical representations of 'High side' pressure/ambient temperature and 'Low side' pressure/evaporator temperature.