Instruction manual

Servicing should only be performed by a Qualied Service Agent

COMMUNICATIONS AND DISPLAYS

Two modes of communications are available to the R7910.

1. The R7910 has two RS485 communication ports for ModBus that allows for interfacing to one or all R7910s of a system

and presents them individually to the user. The S7999D System Operator interface is a color touchscreen display used for

conguration and monitoring of the R7910A. Though conguration can be done through the display, it is not recommended as

all the parameters are pre-congured by the manufacturer. Any custom conguration required by the eld should be done in

consultation with the A. O. Smith qualied service technician. Control Operation and display status in both test and graphical

modes can be shown along with the ability to setup. The R7910 can also be remotely reset through the S7999D display.

2. Either ModBus RS485 communication port can be used to allow conguration and status data to be read and written to the

R7910. Support a Master S7999D or a Building Automation master to control the R7910 to respond to a single ModBus address

to service the requests of the ModBus master in a Lead/Lag arrangement.

SPECIFICATIONS

1. Electrical Ratings:

Operating voltage

• 24VAC (20 to 30 VAC, 60 Hz ±5%)

• 30 amps (Single Heat Exchanger)

• 60 amps (Double Heat Exchanger)

Connected Load for Valve and annunciator functions:

• 24VAC, 60Hz

• 120VAC (+10%/-15%), 60Hz (±5%)

• Model Specic

2. Corrosion:

• R7910A must not be used in a corrosive environment.

3. Operating Temperature: -4°F to 150°F (-20°C to 66°C)

4. Storage/Shipping Temperature: -40°F to 150°F (-40°C to 66°C).

5. Humidity:

• Up to 95% Relative Humidity, noncondensing at 104°F for 14 days. Condensing moisture may cause safety shutdown.

6. Vibration: 0.0 to 0.5g Continuous (V2 level)

7. Enclosure: Nema 1/IP40.

8. Approvals:

Underwriters Laboratories, Inc. (UL): Component Recognized: File No. MP268 (MCCZ)

• R7910 is certied as UL372 Primary Safety Controls.

• The R7910 is certied as UL353 Limit Rated device when using part number 50001464 dual element limit rated NTC sensors.

CSD-1 Acceptable.

Meets CSD-1 section CF-300 requirements as a Primary Safety Control.

Meets CSD-1 section CW-400 requirements as a Temperature Operation control.

Meets CSD-1 section CW-400 requirements as a Temperature High Limit Control when congured for use with 10 kohm NTC sensors.

Federal Communications Commission, Part 15,

Class B. Emissionss.