Johnson Controls A99B Series Catalog Page

FANs 125, 121, 930, 930.5

Product/Technical Bulletin A99

Issue Date 0615

A99B Series Temperature Sensors

The A99B Series Temperature Sensors are passive PTC (Positive Temperature Coefficient) sensors. The A99B sensors are splashproof and are designed to measure temperature in a variety of refrigeration applications. Several accessories allow easy tailoring of the temperature sensor to various mounting configurations.

Applications include temperature sensing for freezers and coolers, as well as in defrost termination sensing, space and return air temperature sensing, and condenser fan cycling.

Figure 1: A99B Temperature Sensors

Features and Benefits

 Variety of Lead Lengths	Encompasses most application requirements
	and simplifies wiring sensors
 Assortment of Mounting	Provides configuration for many
Hardware Available	applications—customizable
 Very Accurate Sensing	Provides excellent performance in a wide
Element	variety of control applications
 Stainless Steel Sensor Bulb	Allows use in more applications than other
	types of bulbs; no corrosion

© 2015 Johnson Controls, Inc.	1
Part No. 24-7664-1636, Rev. A	www.johnsoncontrols.com
Code No. LIT-125186

Application Overview

IMPORTANT: All A99B Series Sensors are designed for use only with 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) that protect against, or warn of, control failure.

The A99B temperature sensor line offers an economical solution for a wide variety of temperature sensing needs in refrigeration and HVAC applications. Typical temperature sensing applications and environments include:

freezers

display cases

walk-in coolers

reach-in coolers

defrost termination temperature sensing

condenser fan cycling

space and return air temperature sensing

outdoor air sensing

process cooling and heating

Sensor Temperature Averaging

Multiple sensors may be wired in a series parallel arrangement to provide an average temperature reading in an area when one sensor cannot provide a representative temperature reading. This can be accomplished with 4, 9, 16, etc., (22, 32, 42, etc.) sensors.

In a series parallel arrangement, there must always be the same number of parallel-connected sensors as there are series connected sensors.

In Figures 2-4, each parallel leg is represented as a column of sensors and each series leg as a row of sensors.

Sensor Sensor

Sensor	Sensor
	To Controller

Figure 2: 4-Sensor Averaging Wiring

Sensor Sensor Sensor

Sensor	Sensor	Sensor
Sensor	Sensor	Sensor
		To Controller

Figure 3: 9-Sensor Averaging Wiring

Sensor Sensor Sensor Sensor

Sensor Sensor Sensor Sensor

Sensor Sensor Sensor Sensor

Sensor Sensor Sensor Sensor

To Controller

Figure 4: 16-Sensor Averaging Wiring

2 A99B Series Temperature Sensors Product/Technical Bulletin

Dimensions

1/4 (6)

2 (50)

Figure 5: A99B Sensor, in. (mm)

Accessories

A99B series accessories include the following:

				1 11/16	1 3/8
				(42)
	9 1/8	1	3/4		(35)
	(229)	(44)
		Sun Shield		4 1/2
		SHL10A-603R		(113.5)
	4 5/16
	(110)

	EMT		PVC Enclosure
	Conduit
			BOX10A-600R
1/2	Adapter
	ADP11A-600R
(13)
	1	4 3/4
		(119)
	(25.4)		3
			(76)	Dia.

			3/8
1/4 (6)		7/8	(9.3)
	1
		(23)
	(25.4)
	Surface Mount Clip
	A99-CLP-1

Figure 6: Available Accessories, in. (mm)

Operation

The A99B sensor incorporates a PTC silicon sensing element whose resistance increases with an increase in temperature. The sensor has a reference resistance of

1,035 ohms at 77 F (25 C). Each element is calibrated according to a standard graph, as shown in Table 2.

The A99B series sensors are typically used with Johnson Controls/PENN System 450™ controls, MR Defrost controls, MS Multi-Stage controls, and A421 Electronic Temperature Controls.

The A99B sensors can also be used with

Johnson Controls System 27 NOVA; A255 fan speed control modules; and R78, DX-9100, XP-9102, XPA-4x1, System 350™ controls, A419 Electronic Temperature controls, and XPA-8x1 products.

Mounting

Mounting Considerations

The A99B sensor may be mounted in virtually any position. To ensure proper operation of the A99B Series sensors, observe the following guidelines:

Mount sensors in areas where they are exposed to representative temperature conditions and sufficient air mixing. Avoid mounting the sensors where air stratification exists.

Avoid areas subject to excessive mechanical vibration or electrical noise.

For outdoor applications, avoid areas where the sensor will be exposed to direct sunlight because this causes the sensor to read a higher temperature. The north side of the building is preferred for outdoor sensors. If not possible, install a sun shield.

Use a thermally conductive paste where appropriate to improve the thermal contact with the sensor.

Do not subject silicon cable (A99BC) to any silicon-based fluids, as this will degrade the cable.

A99B Series Temperature Sensors Product/Technical Bulletin 3