54 Auto Heating & Air Conditioning
Air Pressure Pumps
The air pressure evacuation pump, Figure 3-31, uses
what is known as a venturi effect to operate. The fl ow of
compressed air through an air pressure operated pump
creates a small vacuum that is used to draw air from the
refrigeration system. Air pressure operated pumps are
cheaper but less effective than electrically operated models.
Most air-operated pumps produce less vacuum than an
electric pump, anywhere from one half to one inch less.
This type of pump must be allowed to operate for longer
periods than an electric model.
Recharging Equipment
Once all repairs are completed, the refrigeration system
must be recharged. The simplest method of recharging the
system is to use a gauge manifold, discussed earlier in this
chapter. Remember from Chapter 2 that R-134a containers
are always blue, while R-12 containers are white. Be care-
ful not to mix refrigerants.
Charging Scale
The charging scale allows the technician to charge a
refrigeration system with the proper amount of refrigerant
by weight. Charging by weight is the most accurate way to
recharge a system. The charging scale somewhat resembles
a bathroom scale, Figure 3-32. Most charging scales have
digital readouts. To use a charging scale, place the refriger-
ant container on the scale platform and record its weight.
Then add refrigerant to the system until the weight loss
equals the amount of refrigerant to be added to the system.
Some charging scales allow you to program the amount
of refrigerant to be added to a system. Once the scale is
activated, it will signal when the proper weight of refriger-
ant has been added.
Charging Stations
A charging station combines the features of other
refrigeration service equipment into a single unit. The typical
charging station has gauges and connecting hoses, a stor-
age area for refrigerant cylinders, and a weighing scale or
other device for ensuring the proper amount of refrig erant is
installed. Figure 3-33 shows a typical charging station.
Air Purging Equipment
Most air purging equipment is built into refrigeration
service devices such as recovery/recycling machines and
charging stations. Purging is done automatically by the
internal circuits of the device.
A few charging stations are equipped with a manual
purging device. This device consists of a dual needle gauge,
Figure 3-34. When both needles are in the same position,
all air has been purged. When the needles are in different
positions, the refrigerant cylinder must be purged. To purge
the cylinder, open the cylinder valve until the needles are
in the same position.
Engine Cooling System Test
Equipment
The cooling system is sometimes a source of HVAC
problems. Cooling system test equipment is used to check
the condition of the cooling system and the coolant. Typical
cooling system test equipment is discussed in the following
paragraphs.
Figure 3-31. An air pressure operated vacuum pump is cheaper
but less effi cient than an electric pump. (Snap-On)
Figure 3-32. A simple charging scale enables the technician to
charge the refrigeration system by weight. (TIF Instruments)