Carrier 25HCD Instruction Manual download pdf (Page 8)

Units with Indoor Pistons

Units installed with indoor pistons require charging by the

superheat method.

The following procedure is valid when indoor airflow is within

21 percent of its rated CFM.

1. Operate unit a minimum of 10 minutes before checking

charge.

2. Measure suction pressure by attaching an accurate gage to

suction valve service port.

3. Measure suction temperature by attaching an accurate ther-

mistor type or electronic thermometer to suction line at ser-

vice valve.

4. Measure outdoor air dry–bulb temperature with thermomet-

er.

5. Measure indoor air (entering indoor coil) wet–bulb temper-

ature with a sling psychrometer.

6. Refer to Table 8. Find outdoor temperature and evaporator

entering air wet–bulb temperature. At this intersection, note

superheat. Where a dash (––) appears on the table, do not

attempt to charge system under these conditions or refriger-

ant slugging may occur. Charge must be weighted in,

adding or removing 0.6 oz/ft of 3/8 liquid line above or be-

low 15 ft (4.57 m) respectively.

7. Refer to Table 9. Find superheat temperature located in item

6 and suction pressure. At this intersection, note suction line

temperature.

8. If unit has a higher suction line temperature than charted

temperature, add refrigerant until charted temperature is

reached.

9. If unit has a lower suction line temperature than charted

temperature, reclaim refrigerant until charted temperature is

reached.

10. When adding refrigerant, charge in liquid form into suction

service port using a flow–restricting device.

11. If outdoor air temperature or pressure at suction valve

changes, charge to new suction line temperature indicated

on chart.

12. Optimum performance will be achieved when the operating

charge produces 5_ to 6_F suction superheat at suction

service valve with 82_F outdoor ambient and 80_F

(26.7_C) dry bulb (67_F / 19.4_C) wet bulb) indoor

temperature (DOE “B” test conditions) at rated airflow.

Heating Check Chart Procedure

To check system operation during heating cycle, refer to the

Heating Check Chart on outdoor unit. This chart indicates whether

a correct relationship exists between system operating pressure and

air temperature entering indoor and outdoor units. If pressure and

temperature do not match on chart, system refrigerant charge may

not be correct. Do not use chart to adjust refrigerant charge.

25HBB / 25HBC / 25HCD

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Carrier 25HCD Instruction Manual Page 8

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