Manifold Gauge Set Installation
3. Add refrigerant until the gauges read in the normal range and
the sight glass appears clear. The sight glass may not be clear
for a moment just before or after the clutch cycles on and off
but should generally be clear. Gauge readings will fluctuate
as the compressor cycles on and off.
Note:
Pressures within the air conditioning system vary with
ambient temperature. A normal pressure range is de-
fined as follows:
Low side
15--30 PSIG
High side
150--280 PSIG
If R-134a is used in place of R-12 the high side readings
will be about 20 PSI higher. For this reason many
OEMs are recommending an increase in condenser ca-
pacity when retrofitting to the new refrigerant, R-134a.
If the gauges show any abnormally high or low pres-
sures as you are adding refrigerant, stop and investi-
gate for probable cause. Never add more than one pound
of refrigerant. If the system is low enough on refrigerant
to require more than that amount you should stop and
check again for leaks. Then recover all of the refriger-
ant, repair, evacuate and recharge the air conditioner.
(See Chapter 9). You may want to add dry nitrogen gas
to the AC system instead of R-12 if pressures are below
normal and a leak is suspected. Nitrogen gas is sold in
cylinders under high pressure, 1800 to 2000 PSI. Be
sure the cylinder has a pressure regulating valve to
control the pressure when dispensing nitrogen gas. Dis-
pose the gas at no more than 200-250 psi, as this is
sufficient pressure to cause or indicate a leak point. See
note under Troubleshooting by Manifold Gauge Set
Readings in this chapter.
4. When the gauges show normal, close the hand valve on the
manifold, the hose end shutoff valve, and the valve on the
refrigerant container. You can now proceed with the perfor-
mance inspection.
3. Stabilizing The AC System
For reliable gauge readings as an aid in troubleshooting, the AC system
must be stabilized.
Be sure your tools and test equipment are clear of all
moving parts of the engine and air conditioner.
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