Danfoss Thermostatic expansion valves Service guide

Fitters notes	Thermostatic expansion valves

Contents Page

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Superheat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Subcooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 External pressure equalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Charges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Universal charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	.	.6
MOP charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	.	. 6
MOP ballast charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	.	.7

Thermostatic expansion valve selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. . .9
Orifice assembly replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	10
Danfoss product range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 11

© Danfoss A/S (AC-DSL/MWA), 10 - 2006

DKRCC.PF.000.G1.02 / 520H1459

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Notes

DKRCC.PF.000.G1.02 / 520H1459

© Danfoss A/S (AC-DSL/MWA), 10 - 2006

Fitters notes	Thermostatic expansion valves
Introduction	A thermostatic expansion valve is built up around
	a thermostatic element (1) separated from the
	valve body by a diaphragm.
	A capillary tube connects the element to a bulb
	(2) and a valve body with valve seat (3) and a
	spring (4).
	A thermostatic expansion valve works like this:
	The function of a thermostatic expansion valve is
	determined by three fundamental pressures:
	P1: Bulb pressure which acts on the upper
	surface of the diaphragm, in the valve
	opening direction.
	P2: Evaporating pressure which acts on the
	underside of the diaphragm, in the valve
	closing direction.
	P3: Spring pressure which also acts on the
	underside of the diaphragm, in the valve
	closing direction.
	When the expansion valve regulates, balance is
	created between bulb pressure on one side of the
	diaphragm and evaporating pressure plus spring
	force on the other side.
	The spring is used to set superheat.

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Superheat	Superheat is measured at the point where the
	bulb is located on the suction line and is the
	difference between the temperature at the
	bulb and the evaporating pressure/evaporating
	temperature at the same point.
	Superheat is measured in Kelvin (K) and is used as
	a signal to regulate liquid injection through the
	expansion valve.

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Subcooling	Subcooling is defined as the difference between
	condensing pressure/temperature and liquid
	temperature at the expansion valve inlet.
	Subcooling is measured in Kelvin (K).
	Subcooling of the refrigerant is necessary to
	avoid vapour bubbles in the refrigerant ahead of
	the expansion valve.
	Vapour bubbles in the refrigerant reduce capacity
	in the expansion valve and thereby reduce liquid
	supply to the evaporator.
	Subcooling of 4 5K is adequate in most cases.
		Ad0-0015

© Danfoss A/S (AC-DSL/MWA), 10 - 2006

DKRCC.PF.000.G1.02 / 520H1459

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