Amana ASH13018 Service Manual download pdf (Page 53)

SERVICING

5.0 Defrost Operation

On heat pump units, when the room thermostat is set to the

heating mode, the reversing valve is not energized. As long

as the thermostat is set for heating, the reversing valve will be

in the de-energized position for heating except during a

defrost cycle.

5.1 The heat pump will be on and operating in the heating

mode as described the Heating Operation in section 4.

5.2 The defrost control in the heat pump unit checks to see

if a defrost is needed every 30, 60 or 90 minutes of heat

pump operation depending on the selectable setting by

monitoring the state of the defrost thermostat attached to

the outdoor coil.

5.3 If the temperature of the outdoor coil is low enough to

cause the defrost thermostat to be closed when the

defrost board checks it, the board will initiate a defrost

cycle.

5.4 When a defrost cycle is initiated, the contacts of the

HVDR relay on the defrost board open and turns off the

outdoor fan. The contacts of the LVDR relay on the

defrost board closes and supplies 24Vac to “O” and “W2”.

The reversing valve is energized and the contacts on HR1

close and turns on the electric heater(s). The unit will

continue to run in this mode until the defrost cycle is

completed.

a. For models with defrost control PCBDM133, a 30

second compressor delay at defrost initiation/termina-

tion is optional. As shipped from the factory, the

control is set for the delay (“DLY”), which will turn the

compressor off for 30 seconds while the reversing valve

shifts to/from the cooling mode position. To bypass

the delay, which typically reduces sound levels during

defrost mode, change the pin settings from “DLY” to

“NORM”.

5.5 When the temperature of the outdoor coil rises high

enough to causes the defrost thermostat to open, the

defrost cycle will be terminated. If at the end of the

programmed 10 minute override time the defrost thermo-

stat is still closed, the defrost board will automatically

terminate the defrost cycle.

5.6 When the defrost cycle is terminated, the contacts of the

HVDR relay on the defrost board will close to start the

outdoor fan and the contacts of the LVDR relay will open

and turn off the reversing valve and electric heater(s). The

unit will now be back in a normal heating mode with a heat

pump demand for heating as described in the Heating

Operation in section 4. See section 5.4a.

S-60 ELECTRIC HEATER (OPTIONAL ITEM)

Optional electric heaters may be added, in the quantities

shown in the specifications section, to provide electric

resistance heating. Under no condition shall more heaters

than the quantity shown be installed.

The low voltage circuit in the air handler is factory wired and

terminates at the location provided for the electric heater(s). A

minimum of field wiring is required to complete the installation.

Other components such as a Heating/Cooling Thermostat

and Outdoor Thermostats are available to complete the

installation.

The system CFM can be determined by measuring the static

pressure external to the unit. The installation manual

supplied with the blower coil, or the blower performance table

in the service manual, shows the CFM for the static mea-

sured.

Alternately, the system CFM can be determined by operating

the electric heaters and indoor blower WITHOUT having the

compressor in operation. Measure the temperature rise as

close to the blower inlet and outlet as possible.

If other than a 240V power supply is used, refer to the BTUH

CAPACITY CORRECTION FACTOR chart below.

BTUH CAPACITY CORRECTION FACTOR

SUPPLY VOLTAGE 250 230 220 208

MULTIPLICATION FACTOR 1.08 .92 .84 .75

EXAMPLE: Five (5) heaters provide 24.0 KW at the rated

240V. Our actual measured voltage is 220V, and our

measured temperature rise is 42°F. Find the actual CFM:

Answer: 24.0KW, 42°F Rise, 240 V = 1800 CFM from the

TEMPERATURE RISE CHART, Table 5.

Heating output at 220 V = 24.0KW x 3.413 x .84 = 68.8

MBH.

Actual CFM = 1800 x .84 Corr. Factor = 1400 CFM.

NOTE: The temperature rise table is for sea level installa-

tions. The temperature rise at a particular KW and CFM will

be greater at high altitudes, while the external static pressure

at a particular CFM will be less.

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Amana ASH13018 Service Manual Page 53

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