38MHRC: Service Manual
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
19
SYSTEM EVACUATION AND CHARGING
Refrigerant tubes and indoor coil should be evacuated using the
recommended deep vacuum method of 500 microns. Always break a
vacuum with dry nitrogen.
System Vacuum and Charge
Using Vacuum Pump
1. Completely tighten all flare nuts and connect manifold gage charge
hose to a charge port of the low side service valve (see Fig. 15).
2. Connect the charge hose to vacuum pump.
3. Fully open the low side of manifold gage (see Fig. 16).
4. Start the vacuum pump.
5. Evacuate using the triple evacuation method.
6. After evacuation is complete, fully close the low side of manifold
gage and stop operation of vacuum pump.
7. The factory charge contained in the outdoor unit is good for up to 25
ft. (8 m) of line length. For refrigerant lines longer than 25 ft. (8 m),
add refrigerant as specified in the Table 9 on page 18.
8. Disconnect the charge hose from the charge connection of the low
side service valve.
9. Fully open the B and A service valves.
10. Securely tighten the service valves caps.
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Fig. 15 —Service Valve
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Fig. 16 —Manifold
Deep Vacuum Method
The deep vacuum method requires a vacuum pump capable of pulling a
vacuum of 500 microns and a vacuum gage capable of accurately measuring
this vacuum depth. The deep vacuum method is the most positive way of
assuring a system is free of air and liquid water (see Fig. 17).
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Fig. 17 —Deep Vacuum Graph
Triple Evacuation Method
The triple evacuation method should be used. Refer to Fig. 18 and
proceed as follows:
1. Pump the system down to 500 MICRONS of mercury and allow the
pump to continue operating for an additional 15 minutes.
2. Close the service valves and shut off the vacuum pump.
3. Connect a nitrogen cylinder and regulator to the system and open
until the system pressure is 2 psig.
4. Close the service valve and allow the system to stand for 10 minutes.
During this time, dry nitrogen will be able to diffuse throughout the
system absorbing moisture.
5. Repeat this procedure as indicated in Fig. 18. The system is now free
of any contaminants and water vapor.
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Fig. 18 —Triple Evacuation Method
Final Tubing Check
IMPORTANT: Check to be certain factory tubing on both indoor
and outdoor unit has not shifted during shipment. Ensure tubes are
not rubbing against each other or any sheet metal. Pay close attention
to feeder tubes, making sure wire ties on feeder tubes are secure and
tight.
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment damage
or improper operation.
Never use the system compressor as a vacuum pump.
CAUTION
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