Thermo NESLAB HX 150 Bedienungsanleitung

Refrigeration

Service

Thermo Manual P/N U00058

Rev. 09/09/97

NESLAB HX 150

Recirculating Chiller

No part of this publication may be

reproduced or reprinted except for

personal use without the prior permission

of Thermo Electron.

Contents

General Information

After Sale Support ..................................................................................................... 2

CAUTION .................................................................................................................. 3

Theory of operation ................................................................................................... 4

Cool mode ............................................................................................................ 4

Heat/idle mode...................................................................................................... 5

Troubleshooting

Troubleshooting Chart: Runaway cold ...................................................................... 6

Troubleshooting Chart: Runaway hot........................................................................ 7

Troubleshooting Chart: Weak cooling ...................................................................... 8

Troubleshooting Chart: Refrigeration pressures..................................................... 10

Replacement

Compressor............................................................................................................. 11

Fan Motor ................................................................................................................ 13

Filter/dryer ............................................................................................................... 14

Solenoid valve......................................................................................................... 15

Tank coil assembly (TCA) ....................................................................................... 17

Water regulating valve............................................................................................. 21

Capillary tube........................................................................................................... 23

Refrigeration components (general) ........................................................................ 25

Procedures

Speed check............................................................................................................ 27

Suction Discharge pressure and speed check ........................................................ 28

Condenser maintenance (air cooled & water cooled).............................................. 29

Flushing (closed facility system).............................................................................. 29

Flushing (tap water system) .................................................................................... 30

Flushing (unit off)..................................................................................................... 31

Commercial flushing chemicals ............................................................................... 32

Hot gas valve (Automatic Discharge Relief (ADR)) ................................................ 33

Schrader valves....................................................................................................... 37

Leak test and repair of leak ................................................................................ 38

Solenoid coil test ..................................................................................................... 39

Solenoid valve rebuild ............................................................................................. 40

Tank Coil Assembly (TCA) failure and repair ........................................................ 42

Water regulating valve setting ................................................................ 43

Reference

Refrigeration Specifications ................................................................... 44

R22 pressure-temperature chart ............................................................ 45

Heat load calculation .............................................................................. 46

Condenser re uirements: Air-cooled units ............................................ 47

Condenser re uirements: Water-cooled units ....................................... 48

15-pin accessory connector (optional) pinout ......................................... 49

Part numbers ......................................................................................... 50

This section is intended for use by qualified refrigeration techni-

cians only. Servicing refrigeration systems is hazardous and

must be performed only by qualified persons.

Refrigeration systems contain various hazards, including (but

not limited to) the following:

1. Refrigeration systems contain refrigerant gases at very high

pressures, even when not running.

2. Sudden release of refrigerant gases will result in rapid expan-

sion and severe frostbite hazard. Refrigerant gases will

cause severe injury to unprotected flesh.

3. Refrigerant gases are not flammable and are chemically

inert. However, they are heavier than air and will displace

oxygen. They can cause suffocation if released in a confined

area.

4. Refrigerant gases used in this product are classified as

Ozone Depleting Chemicals by the US Environmental Protec-

tion Agency. While they pose no hazard sealed inside the

refrigeration system, intentional release into the atmosphere

is outlawed under the 1990 Clean Air Act.

5. Compressor start and run capacitors store hazardous levels

of electricity, even when the unit is not running or plugged in.

6. Refrigeration system components operate at high tempera-

tures and present a severe burn hazard.

CAUTION

THEORY OF OPERATION

The chiller operates in two modes: COOL or HEAT/IDLE. The

controller compares setpoint to actual temperature and decides

which mode is required. This is a thermostatic (not proportional)

control system. The compressor, pump, and fan motor all run

continuously, regardless of mode.

The thermal transfer of the HEAT/IDLE mode is not as efficient

as the COOL mode. This results in units running at little or no

load to spend most of their time in the HEAT/IDLE mode with

brief periodic COOL periods. A duty cycle of 20% COOL / 80%

HEAT/IDLE may be typical for units running under no load. This

duty cycle will reverse as increasing load is applied, reaching

100% COOL / 0% HEAT/IDLE at full load.

This system results in tighter temperature control than continu-

ally cycling the compressor on and off, as is typical in a house-

hold refrigerator.

The default mode is HEAT/IDLE. A failure of the temperature

sensor or controller will generally result in the HEAT/IDLE

mode. This prevents a possible freezing of the cooling fluid and

resulting damage from fluid expansion.

COOL MODE

If the setpoint is below the actual temperature, the controller is

in COOL mode. The controller triac output provides a closure

to supply line voltage to the solenoid coil. The solenoid valve,

which is normally-closed, is then pulled open by the coil and a

standard refrigeration cooling loop exists.

Refrigerant,asagas,ispressurizedinthe compressor.Itthen

enters the condenser and changes to a liquid due to the cooling

provided by the fan and condenser fins. Heat is given up to the

air at this point. The liquid refrigerant exits the condenser and

passes through a filter/dryer which traps contaminants and

absorbs any water moisture in its desiccant element. The refrig-

erant then passes through the open solenoid valve and enters

the capillary tube. The restriction of the tube meters the flow.

The capillary tube ends at the evaporator.

The evaporator is a coil located inside the fluid tank. As the

liquid refrigerant encounters the increased volume of the evapo-

rator, it expands tremendously, changing from a liquid to a gas,

and absorbing heat from the fluid (cooling it) in the process. The

refrigerant, now a gas, exits the evaporator and passes through

the suction filter. The refrigerant then enters the compressor at

low pressure and is re-compressed.

HEAT/IDLE MODE

If the setpoint is above the actual temperature, the controller is

inHEAT/IDLEmode. The triacoutputopens,turningthe solenoid coiloff.The

solenoidvalvethendropsclosed. This closed valve stops theflowofrefrigerant.

Duringthe heat/idle mode whentheliquidline solenoid valve isclosed,the

pressure drops in the suction line back to the compressor. When the pressure

dropstoa predetermined value, thehotgasbypassvalvewill open and allow

hotgas to flowtothe evaporator asstated.Thehot gas valveopenson a

decrease in pressure on its discharge port. The discharge port is connected to

theevaporator side ofthesystem.Therefrigerant gas isnowrouteddirectly to

the evaporator. The gas is not allowed to condense, as it has bypassed the

condensercompletely.Thehotgas passing through the evaporator

coil adds some heat to the fluid, then returns directly through the suction filter

tothe compressor.Thisunloads the compressor, resultinginlowerdischarge

pressure,highersuction pressure, and lesspowerconsumption.Observingthe

suction pressure in this mode will indicate the setting of the Hot Gas (ADR)

valve.

START

Setpoint

< actual

Calibration

error

YES

Replace

valve

Valve is

mechanically OK

Test

STOP

Refer to

ELECTRICAL & CONTROL

section

Remove coil

from valve

Drawing 67.cfl

Rick Mills

13 March 1995

YES

Valve is

stuck open

Not a

Refrigeration

Problem

Problem is in

Controller or

sensor

See VALVE

REPLACEMENT

Does

unit

warm up?

YES

UNSURE

YESNO

Can you

get cool

lamp off? *

cool lamp

on?

* by manipulating setpoint

coil

on?

Normal

Response

Troubleshooting Chart: Runaway cold

START

Setpoint

> actual

Normal

response

Calibration

Error

YES

Replace

valve

Test

STOP

Refer to

ELECTRICAL & CONTROL

section

Drawing 68.cfl

Rick Mills

13 March 1995

YES

Valve is

stuck closed

Not a

refrigeration

problem

See VALVE

REPLACEMENT

UNSURE

Can you

get cool

lamp on? *

cool lamp

on?

YES

NO YES

YES

*by manipulating setpoint

See TROUBLESHOOTING:

"WEAK COOLING"

Any

DC volts

on coil

Any

AC volts

on coil

coil

on?

Problem is in

Controller or

Sensor

Is it

cooling

at all ?

Troubleshooting Chart: Runaway hot

Troubleshooting Chart: Weak cooling

Troubleshooting Chart: Weak cooling continued

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