Condenser (Small A/C); Adding Vapor State Refrigerant - PREVOST H3-41 Maintenance Manual

SECTION 22: HEATING AND AIR CONDITIONING
NOTE
During this operation, care must be taken not
to fill the receiver tank over the upper sight
glass. If so, stop process immediately. Always
allow refrigerant piping and units to warm up
to the ambient air temperature before opening
system or sweating will take place inside the
lines.
6.5.5

Adding Vapor State Refrigerant

Addition of vapor state refrigerant is carried-out
to compensate for hose permeation and shaft
seal losses over a long period and is done from
the suction side while compressor is in
operation.
A typical sign of refrigerant low charge would be
A/C lower performance experienced by the user.
Perform the usual leak inspection and correct
any leaks before adding refrigerant.
Verification
Perform the following verifications:
1- A vehicle stopped for more than 4 hours
should show the lower receiver tank sight
glass full at room temperature or with some
level if ambient temperature is high. This
method is less accurate when ambient
temperature gets high.
2- With the AC on for at least 10 minutes, the
moisture indicator sight glass (FIGURE 82)
should be clear, not milky, without bubbles
in the stream of refrigerant. Bubbles in the
moisture indicator sight glass are sign of
refrigerant low charge. The filter-dryer
nearby should
temperature, less than 5°F differential
between inlet and outlet. A partially blocked
filter will make some flash gas and give a
"milky" sight glass.
66 PA1621 Maintenance Manual All Series | Revised February 2019
be near constant
FIGURE 82: MOISTURE INDICATOR SIGHT GLASS
3- At fast idle, the high side pressure should
be near the following calculation: add 30° F
to the ambient temperature in Fahrenheit.
In the refrigerant chart (see paragraph 5.8),
find this temperature and the corresponding
saturation pressure and add 10 psi for the
pressure drop between compressor and
condenser.
Calculation example:
At 70°F outside, add 30°F. In the chart
(paragraph 5.8 ), find the pressure value for a
temperature of 100°F. For 134a refrigerant
gas, you will find a value of 124 psi. Add 10
psi to this value for the compressor to
condenser line, this result gives 134 psi. So a
high side pressure value between 129 to 139
psi should be OK.
Refrigerant addition
NOTE
Use a bottle that is more than half full.
Always charge the system with the cylinder
upright and the valve on top to avoid drawing
liquid out of the cylinder.
1. Install a heated refrigerant bottle at the
back of the vehicle, on a scale, straight up.
Refer to section "Precautions in Handling
Refrigerant" for the proper heating method.
2. Connect the yellow hose of your manifold
gage set to the red (vapor) valve on the
bottle. Connect the blue valve of the gage
set on the suction shutoff valve service port
of the compressor. Connect the red valve of
the gage set to the discharge shutoff valve
service port. Hoses should be purged of air
at installation (evacuated).