Johnson Controls A70 Series Installation Sheets Manual

121 Temperature Controls Section Technical Bulletin A70, A72 Issue Date 0591 © 1991 Johnson Controls, Inc. 1 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.

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.

! 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