Johnson Controls A70 Series Manual de usuario

Installation Sheets Manual 121

Temperature Controls Section

Technical Bulletin A70, A72

Issue Date 0591

Code No. LIT-121121

Part No. 997-202, Rev. E

A70, A72 Series Temperature Controls A70 Single-Pole and

Four-Wire Two-Circuit A72 Two-Pole Construction

Application

The A70 single-pole and A72

two-pole controls incorporate a

load-carrying, contact structure

which provides direct control of

AC motors within the control

rating. (See cover label for

electrical rating.)

All Series A70, A72 controls are

designed for use only as

operating controls. Where an

operating control failure would

result in personal injury and/or

loss of property, it is the

responsibility of the installer to

add devices (safety, limit

controls) or systems (alarm,

supervisory systems) that

protect against, or warn of,

control failure.

Operation

Controls are available with either

CLOSE high -- OPEN low or

OPEN high -- CLOSE low

contact action for heating or

refrigeration applications. The

snap-acting contacts are

operated by a temperature

sensing element. On the

A70 controls with auxiliary

contact, the auxiliary contact

closes to actuate a signal or

other auxiliary circuit at the

same time the main contact

opens. (See Fig. 6.)

Installation

Mounting

The A70 control in the NEMA 1

enclosure must be located in

areas protected from the direct

effects of weather. If the control

is directly exposed to the

weather or other wet

environments, it must be

equipped with an outdoor

enclosure. Mount the control on

a flat surface or panel board by

two screws or bolts through the

holes in the back of the case.

Controls are supplied without

brackets unless specified. The

standard bracket is Part Number

271-350. The desired mounting

position is with the element

bellows pointing down.

General Instructions

1. Avoid sharp bends or kinks

in the capillary tubing.

2. Style 1 (for clamp contact or

liquid immersion) -- be sure

the bulb is securely

clamped to the evaporator

coil, or is completely

immersed in the liquid.

3. Style 18 for air temperature

control -- locate the bulb

where there is free air

circulation. Make sure the

bulb does not contact a wall

surface.

4. Make sure the equipment's

electrical load is not in

excess of the control's

electrical rating.

5. Coil and secure the excess

capillary length to avoid

vibration. Allow some slack

in the capillary to avoid

“violin string” vibration which

can cause the tubing to

break. Do not allow the

tubing to rub against metal

surfaces where friction can

damage the capillary.

6. Do not use the control on

applications where

temperature exceeds the

maximum allowable

temperature. See the

Maximum Bulb Temperature

table.

Fig. 1 -- A70 Temperature

Control with a style 1 sensing

element.

2 A70, A72 Technical Bulletin

7. Take the following steps

when mounting a control

with a vapor-pressure

sensing element. (See

Fig. 9.)

a. Mount the control with

the power element

down.

b. Mount the control and

bulb at approximately

the same level.

c. Mount the bulb with the

free (sealed) end lower

than the capillary end.

Note: On cross

ambient models the

side of the bulb marked

“TOP” should always

be up.

CAUTION: Do not dent or

deform the sensitive bulb of

this control. A dent or

deformation will change the

calibration and cause the

control to cycle at a

temperature lower than the

dial setting. When a bulb

mounting clip is used to

mount the bulb near the

refrigerant tubing, be sure

the sheet metal screw does

not pierce the tubing.

Wiring

CAUTION: Disconnect the

power supply before the

wiring connections are

made to avoid possible

electrical shock or damage

to the equipment. On

multiple circuit units, more

than one circuit may have

to be disconnected.

Make all wiring connections

using copper conductors only,

and in accordance with the

National Electrical Code and

local regulations. For maximum

electrical rating of the control,

see the electrical rating shown

on the inside cover label of the

control.

The contacts on the single-pole

A70 controls with main and

auxiliary contacts are identified

on the contact block. The main

contacts are LINE-M2 and the

auxiliary contacts are LINE-M1.

The action of the main contacts

are shown on the cover label.

Figure 6 shows a typical wiring

hookup.

Where it is desirable for the user to

increase or decrease the DIFFERENTIAL

ONLY, external adjusting knob is supplied

on differential screw as shown in Fig. 4.

Knob is provided with stops and factory

assembled to permit change only within a

specified range.

External adjusting knob may be placed on range

screw, as shown in Fig. 5, where it is necessary

for the user to raise or lower both CUT-IN and

CUT-OUT points (differential remains constant).

Knob is provided with stops and factory

assembled to permit adjustments within a

specified range.

NOTE: Knob is usually factory assembled in

either position as shown in Figs. 4 or 5 above,

depending upon specifications of original buyer.

However, knob may be changed in the field

from the differential to the range screw or vice

versa by loosening set screw and removing

knob and indicator plate and reversing their

positions. Assuming that knob is factory

assembled on range screw (Fig. 5) and set to

restrict adjustment to 10F° (5.6C°), adjustment

will be restricted to approximately 5F°(2.8C°) if

knob is placed on differential screw

(Fig. 4).

MANUAL RESET

BUTTON

Manual button shown in

Fig. 3, left, when

supplied provides

MANUAL START only.

Button must be pushed

and released to restart

after lockout occurs.

Fig. 7 -- Interior view of “Open Low”

temperature control showing how to adjust

the set point and differential.

Fig. 8 -- Interior view of “Open High”

temperature control showing how to adjust

the set point and differential.

A70, A72 Technical Bulletin 3

CAUTION: Use No. 8-32 ×

1/4 in. terminal screws.

Longer screws can interfere

with the switch mechanism

and damage the switch.

Adjustment

The controls have a single

“sight-set” calibrated scale which

shows both the cut-in and cutout

settings. Adjustments can be

made without removing the

control cover. (See Figs. 7

and 8.)

If the control is equipped with

lockout, the contacts must be

reset manually after lockout

occurs. (See Fig. 3.)

Checkout Procedure

The operating point of the

control should be confirmed by

an accurate thermometer.

Before leaving the installation,

observe at least three complete

operating cycles to be sure that

all components are functioning

correctly. If the control setting is

outside the normal operating

range of the controlled device,

the operation of the control

should be simulated by

actuating the contacts to confirm

that the electrical connections

are correct.

Repairs and Replacement

Field repairs must not be made

except for replacement of the

cover and knob. For a

replacement control, cover or

knob, contact the nearest

Johnson Controls wholesaler.

Controls Group

507 E. Michigan Street

P.O. Box 423 Printed in U.S.A.

Milwaukee, WI 53202

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