14-17. AIR-CONDITIONING SYSTEM SERVICING (R-12) (Cont'd)
Never mix R-134a and R-12 refrigerants. They are incompatible
and will cause severe damage to system components if mixed.
Whenever any air-conditioning vapor system component needs
replacement, the system must be discharged, flushed, and a new
The following procedure applies to vehicles with R-12 refrigerant
only. Refer to para. 14-27.1 for vehicles with R-134a refrigerant.
a. Manifold Gauge Set Installation
Turn high pressure gauge valve (2) and low pressure gauge valve (1) on gauge set (3) clockwise to
their front-seated (closed) positions.
Remove two dust caps (9) from service valves (6) and (7).
Ensure both service valve shafts (11) are moved fully counterclockwise until in back-seated
Remove two cap nuts (8) from service valve ports (10) and (12).
Make sure hand valves on manifold gauge set are in closed
position during connection, and hoses are clear of any moving
parts in engine compartment. Injury to personnel or damage to
equipment may result.
Connect low pressure gauge hose (5) on manifold gauge set (3) to suction (low side) service valve
Connect high pressure gauge hose (4) on manifold gauge set (3) to discharge (high side) service
Hang manifold gauge set (3) so that hoses (5) and (4) are well away from moving engine parts.
Service valve mid-seated position is used for discharging, flushing,
evacuating, charging, and testing.
Do not perform step 9 if system is already evacuated. High and
low pressure hoses must be purged with R-12 for charging
purposes (refer to task f.)
Turn both service valve shafts (11) to mid-seated position.
Loosen low pressure gauge hose (5) and high pressure gauge hose (4) at manifold gauge set slightly
for a second to purge air from hoses, and then tighten.