Armstrong Air Conditioning 4HP13 Istruzioni per l'installazione e l'avvio - Pagina 8

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Compressor Delay

The defrost board has a field-selectable function to

reduce occasional sounds that may occur while the unit is

cycling in and out of the defrost mode. The compressor will

be cycled "off" for 30 seconds going in and out of the defrost

mode when the compressor delay jumper is removed.

NOTE: The 30 second "off" cycle is not functional when

jumpering the TEST pins.

Time Delay

The timed-off delay is 5 minutes long. The delay help to

protect the compressor from short-cycling in case the power

to the unit is interrupted or a pressure switch opens. The

delay is bypassed by placing the timer select jumper across

the TEST pins for 0.5 seconds.

Pressure Switch Circuit

The defrost control incorporates 2 pressure switch

circuits. The optional high pressure switch connects to the

boards HI PS terminals. The low pressure switch is factory

installed.

During a single demand cycle, the defrost control will

lock out the unit after the fifth time that the circuit is

interrupted by any pressure switch wired to the control board.

In addition, the diagnostic LEDs will indicate a locked-out

pressure switch after the fifth occurrence of an open

pressure switch. The unit will remain locked out until power

to the board is interrupted, then re-established or until the

jumper is applied to the TEST pins for 0.5 seconds.

NOTE: The defrost control board ignores input from the

low-pressure switch terminals as follows:

! During the TEST mode,

! During the defrost cycle,

! During the 90 second start-up period,

! and for the first 90 seconds each time the reversing

valve switches heat/cool modes. If the TEST pins

are jumpered and the 5 minute delay is being by-

passed, the LO PS terminal signal is not ignored

during the 90 second start-up period.

Page 8 of 17

DEMAND DEFROST SYSTEM DESCRIPTION

The demand defrost controller measures differential

temperatures to detect when the system is performing poorly

because of ice build-up on the outdoor coil. The controller

"self-calibrates" when the defrost system starts and after

each system defrost cycle. The defrost control board

components are shown below.

The control monitors ambient temperature, outdoor coil

temperature, and total run time to determine when a defrost

cycle is required. The coil temperature probe is designed

with a spring clip to allow mounting to the outside coil tubing.

The location of the coil sensor is important for proper defrost

operation.

NOTE - The demand defrost board accurately measures

the performance of the system as frost accumulates

on the outdoor coil. This typically will translate into

longer running time between defrost cycles as more

frost accumulates on the outdoor coil before the board

initiates defrost cycles.

DIAGNOSTIC LEDS

The state (Off, On, Flashing) of two LEDs on the defrost

board (DS1 [Red] and DS2 [Green]) indicate diagnostics

conditions that are described in table.

Mode

No power to control

Normal operation/

power to control

Anti-short cycle

lockout

Low pressure switch

fault (Optional)

Low pressure switch

lockout (Optional)

High presssure switch

fault (Optional)

High pressure switch

lockout (Optional)

Issue 0946

Green Led (DS2)

Red Led (DS1)

OFF

Simultaneous Slow Flash

Alternating Slow Flash

Slow FLASH

OFF

Slow FLASH

OFF

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