4-3
©
2012 Mobile Climate Control
T-348 Rev. 07/2012
4.4 SUCTION AND DISCHARGE SERVICE VALVES
The suction and discharge service valves (Figure 4-3)
are provided with a double seat and a gauge port,
which allows servicing of the compressor and
refrigerant lines.
Turning the valve stem counterclockwise (all the way
out) will
backseat
the valve to open the line to the
compressor and close off the gauge port. In normal
operation, the valve is backseated to allow full flow
through the valve. The valve should always be
backseated before removing the gauge port cap.
Turning the valve stem clockwise (all the way
forward) will
frontseat
the valve to isolate the
compressor line and open the gauge port.
To measure suction or discharge pressure, midseat
the valve by opening the valve clockwise 1/4 to 1/2
turn. With the valve stem midway between
frontseated and backseated positions, the suction or
discharge gauge port is open to both the compressor
and the line.
SERVICE
PORT (R--22)
VALVE STEM CAP
VALVE
STEM
TO DISCHARGE OR
FROM SUCTION LINE
PORT TO
COMPRESSOR
Service Valve
Frontseated
(clockwise)
Service Valve
Backseated
(counterclockwise)
ACCESS VALVE
(R--134a)
ACCESS VALVE CAP
Figure 4-3 Suction or Discharge Service Valve
4.4.1 Installing R-134a Manifold Guage Set
A R-134a manifold gauge/hose set with self-sealing
hoses is required for service of models covered
within this manual. The manifold gauge/hose set is
available from Mobile Climate Control Transicold.
(Mobile Climate Control P/N 07-00294-00, which
includes items 1 through 6, Figure 4-4). To perform
service using the manifold gauge/hose set, do the
following:
a. Preparing Manifold Gauge/Hose Set For Use
1. If the manifold gauge/hose set is new or was
exposed to the atmosphere it will need to be eva
cuated to remove contaminants and air as follows:
2. Back seat (turn counterclockwise ) both field ser
vice couplers (see Figure 4-4) and midseat both
hand valves.
3. Connect the yellow hose to a vacuum pump and
an R-134a cylinder.
4. Evacuate to 10 inches of vacuum and then charge
with R-134a to a slightly positive pressure of 1.0
psig.
5. Front seat both manifold gauge set hand valves
and disconnect from cylinder. The gauge set is
now ready for use.
b. Connecting Manifold Gauge/Hose Set
To connect the manifold gauge/hose set for reading
pressures, do the following:
1. Remove service valve stem cap and check to make
sure it is backseated. Remove access valve cap.
2. Connect the field service coupler (see Figure 4-4)
to the access valve.
3. Turn the field service coupling knob clockwise,
which will open the system to the gauge set.
4. Read system pressures.
5. Repeat the procedure to connect the other side of
the gauge set.
c. Removing the Manifold Gauge Set
1. While the compressor is still ON, backseat the
high side service valve.
2. Midseat both hand valves on the manifold gauge
set and allow the pressure in the manifold gauge
set to be drawn down to low side pressure. This
returns any liquid that may be in the high side hose
to the system.
CAUTION
To prevent trapping liquid refrigerant in
the manifold gauge set be sure set is
brought to suction pressure before dis
connecting.
3. Backseat the low side service valve. Backseat both
field service couplers and frontseat both manifold
set hand valves. Remove the couplers from the
access valves.
4. Install both service valve stem caps and access
valve caps (finger-tight only).
