2. INSPECT REFRIGERAT PRESSURE WITH MANIFOLD
GAUGE SET
This is a method in which the trouble is located by using a manifold
gauge set. Read the manifold gauge pressure when the
these conditions are established:
Test conditions:
Temperature at the air inlet with the switch set at RECIRC
is 30 – 35°C (86 – 95°F)
Engine running at 1,500 rpm
Blower speed control switch set at high
Temperature control set at max. cool
HINT:
It should be noted that the gauge indications may vary slightly
due to ambient temperature conditions.
(1) Normally functioning refrigeration system.
Gauge reading:
Low pressure side:
0.15 – 0.25 MPa (1.5 – 2.5 kgf/cm2)
High pressure side:
1.37 – 1.57 MPa (14 – 15 kgf/cm2)
From
http://www.onlineconversion.com/pressure.htm
1.5 kilogram-force/square centimeter = 21.335015 pound/square inch [absolute]
2.5 kilogram-force/square centimeter = 35.5583583 pound/square inch [absolute]
Same as what R2 said,
14 kilogram-force/square centimeter = 199.1268067 pound/square inch [absolute]
15 kilogram-force/square centimeter = 213.35015 pound/square inch [absolute]
We are reading gauge pressure here not absolute pressure but the absolute should not skew the results as we are converting from another gauge pressure, not something like:
1 atmosphere [standard] = 14.6959503 pound/square inch [absolute]
Here is some info on reading the sight glass, IMO it is only for troubleshooting purposes not servicing the system. Note the test conditions.
ON–VEHICLE INSPECTION
1. INSPECT REFRIGERANT VOLUME
Observe the sight glass on the liquid tube.
Test conditions:
Running engine at 1,500 rpm
Blower speed control switch set at ”HI”
A/C switch ON
Temperature control set at ”MAX. COOL”
Fully open doors
Item Symptom Amount of refrigerant Remedy
1 Bubbles present in sight glass Insufficient*
1. Check for gas leakage with gas leak
tester and repair if necessary
2. Add refrigerant until bubbles disappear
2 No bubbles present in sight glass None, sufficient or too much Refer to items 3 and 4
3
No temperature difference between
compressor inlet and outlet
Empty or nearly empty
1. Check for gas leakage with gas leak
tester and repair if necessary
2. Add refrigerant until bubbles disappear
4
Temperature between compressor inlet and
outlet is noticeably different
Correct or too much Refer to items 5 and 6
5
Immediately after air conditioning is turned
off, refrigerant in sight glass stays clear
Too much
1. Discharge refrigerant
2. Evacuate air and charge proper
amount of purified refrigerant
6
When air conditioning is turned off,
refrigerant foams and then stays clear
Correct –
*: Bubbles in the sight glass with ambient temperatures higher
than usual can be considered normal if cooling is sufficient.
“higher than usual” for GA? ID? or Tokyo?
And IMO the most accurate way to service the system is by weight, it does not change with ambient conditions (temperature, pressure, altitude, humidity ) and vehicle state (door open/closed, AC control setting, RPM, engine bay temperature etc) also this is the only spec given under SERVICE DATA, servicing by weight does require removing all the old refrigerant and vacuuming down the system and has not been popular with those on this forum in the past.
Refrigerant charge volume 850 +/- 50 g (59.98 +/- 1.76 oz.)
Edit, incorrect see post #15 and #17 below.
Failing that service it by pressure with a full gauge set. Remember to purge the lines to prevent introduction of air into the system.
I have a coworker that has charged his system by temperature of the outlet air, he slowly adds refrigerant until the temperature bottoms and just starts to come back up, he has added a different compressor and therefore changed the volume of the system.
Seams to be it would be best to watch all 4 indicators when servicing, in descending order of importance: weight, pressure, outlet temperature, and sight glass.
