1999 DODGE RAM Service Repair Manual

Because R-134a is not interchangeable with R-12, separate
sets of hoses, gauges, and recovery/recycling equipment are required
to service vehicles. This is necessary to avoid cross-contamination
and damaging system.
All equipment used to service systems using R-134a must meet
SAE standard J2210. The service hoses on the manifold gauge set must
have manual (turn wheel) or automatic back-flow valves at the service
port connector ends. This will prevent refrigerant from being released
into the atmosphere.
For identification purposes, R-134a service hoses must have a
Black stripe along their length and be clearly labeled SAE J2196/134a.
The low pressure test hose is Blue with a Black stripe. The high-side
test hose is Red with a Black stripe. The center test hose is Yellow,
or White, with a Black stripe.
NOTE: Refrigerant R-12 service hoses will ONLY be labeled SAE
J2196.
All R-134a manifold gauge sets can be identified by one or
all of the following:
* Labeled FOR USE WITH R-134a on set.
* Labeled HFC-134 or R-134a on gauge face.
* Light Blue color on gauge face. In addition,
pressure/temperature scales on R-134a gauge sets are
different from R-12 manifold gauge sets.
MANIFOLD GAUGE SET
A manifold gauge set is used to determine the system's high-
side and low-side pressures, correct refrigerant charge, and operating
efficiency. High (discharge) and low (suction) pressures must be
compared to determine system operation. Manifold gauge sets for the 2
refrigerant types are basically the same except for fittings at ends
of hoses. Fittings are different to ensure connection only to
appropriate refrigerant system.
Low-Side Gauge
Low-side gauge, which may have a Blue identifying feature, is
used to measure low-side (suction) pressure. Low-side gauge is also
called a compound gauge because it can measure pressure and vacuum.
Pressure scale ranges from 0 to 150 psi; vacuum scale ranges from 0 to
30 in. Hg.
High-Side Gauge
High-side gauge, which may have a Red identifying feature, is
used to measure high-side (discharge) pressure. Gauge scale ranges
from 0 to 500 psi.
CONNECTING GAUGE SET
NOTE: R-134a quick disconnect service couplings are connected in
the same sequence as Schrader-type service valves.
Schrader-Type Valves
1) Put on safety goggles, and cover vehicle's fender. Slowly
remove protective caps from Schrader valves to check for leaky valves.
CAUTION: Ensure hand valves on manifold gauge set and the hose-end
shutoff valves are closed before attaching test hoses to
Schrader valves.

2) Ensure service hoses are equipped with valve core
depressor to match Schrader valve. If not, install special adapters
for this purpose. If the high-side service hose connector will not fit
on high-side Schrader valve, a special adapter must be used. See
SPECIAL VALVE CONNECTORS.
3) Ensure both manifold gauge set hand valves are closed.
Connect low-side service hose to low-side (suction) service valve, and\
finger tighten connections. Connect high-side service hose to high-
side (discharge) service valve, and finger-tighten connections.
NOTE: After test gauges are installed, test hoses must be purged of
all air before proceeding with testing.
PURGING TEST HOSES
1) Ensure high-side and low-side hoses are properly connected
to service valves, and all hose connections are tight. Place a clean
shop towel over end of center service hose.
2) Purge high-side test hose by opening hand valve on high-
side gauge for 3-5 seconds. This allows the system's refrigerant to
force air through test hoses and out of center service hose into the
shop towel. Immediately close high-side gauge hand valve.
3) Purge low-side test hose in the same manner using hand
valve of low-side gauge. Close hand valve after 3-5 seconds. Purging
of test hoses is now complete, and system is ready for testing.
NOTE: If manifold gauge set is to be used in conjunction with
refrigerant recovery/recycling equipment, use instructions
provided with the recovery/recycling equipment to properly
purge test hoses.
STABILIZING A/C SYSTEM
1) Once manifold gauge set is attached to system and test
hoses have been purged, the system is ready for testing. Place all
test hoses, gauge set and other equipment away from all moving parts
of engine.
2) Start engine, and turn A/C controls to maximum cooling
position (full cold or MAX A/C). Set blower on high speed. Open doors
and/or windows. Operate system for 5-10 minutes. System should now be
stabilized and ready for test readings.
PRESSURE-TEMPERATURE RELATIONSHIP
A refrigerant, when confined in an enclosed space, increases
in pressure as the temperature increases. Conversely, if the
temperature is lowered, the pressure also decreases.
Depending on temperature, a corresponding pressure will exist
in such an enclosed space. For example, at 70
F (21.1C) a gauge will
indicate about 71.0 psi (5.0 kg/cm). The R-134a PRESSURE- TEMPERATURE
RELATIONSHIP table shows this relationship.
R-134a PRESSURE-TEMPERATURE RELATIONSHIP









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Temperature F (C) ( 1) psi (kg/cm)
20 (-6.7) ................................................. 18 (1.3\
)
30 (-1.1) ................................................. 26 (1.8\
)
40 (4.4) .................................................. 35 (2.5\
)
50 (10.0) ................................................. 45 (3.2\
)
60 (15.6) ................................................. 57 (4.0\
)

70 (21.1) ................................................. 71 (5.0\
)
80 (26.7) ................................................. 87 (6.1\
)
90 (32.2) ................................................ 104 (7.3\
)
100 (37.8) ............................................... 124 (8.7\
)
110 (43.3) .............................................. 147 (10.3\
)
120 (48.9) .............................................. 171 (12.0\
)
130 (54.4) .............................................. 199 (14.0\
)
140 (60.0) .............................................. 229 (16.1\
)
150 (65.6) .............................................. 263 (18.5\
)
160 (71.1) .............................................. 300 (21.1\
)
(1) - Pressure readings are provided as a general guideline and may
not represent actual readings.









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PRESSURE GAUGE READINGS
The pressure gauge readings shown represent an expansion
valve type system using a Nippondenso 10-cylinder compressor. See
Figs. 9 -17. Gauge indications will vary depending on system
configuration and compressor application.
Temperature and humidity, as well as other factors, affect
pressure gauge readings. Compared to R-12 systems, pressure readings
on R-134a systems are generally lower for low-side pressure and higher
for high-side pressure. Pressure gauge readings should be used only as
a guide.
NOTE: For additional information, see latest MITCHELL AUTOMOTIVE
AIR CONDITIONING BASIC SERVICE TRAINING MANUAL.
Fig. 9: Normally Functioning R-134a A/C System

Fig. 10: Some Moisture In R-134a System
Fig. 11: Low R-134a Charge

Fig. 12: Poor R-134a Refrigerant Circulation
Fig. 13: No R-134a Refrigerant Circulation

Fig. 14: Insufficient Cooling Of Condenser Or R-134a Refrigerant
Overcharge

Fig. 15: Air In R-134a System

Fig. 16: Expansion Valve Improperly Mounted Or Heat Sensing Tube
Defective (Opening Too Wide)
Fig. 17: Compressor Malfunction