Communication Failures, Alarms and Alerts

AUX1 is not blinking, check the DIP switch positions on the board. If the red LEDs are not blinking in unison, verify that correct power is being supplied to all modules. A blinking red LED at the rate of once per second means that software is not loaded on the board. Also, be sure that the board is supplied with the current software. If necessary, reload current software. A board LED that is lit continuously should be replaced.

Green LED

The MBB, ECB and AUX1 each have one green LED. The Local Equipment Network (LEN) LED should always be blinking whenever power is on. If LEN LED is not blinking, check LEN connections for potential communication errors (MBB J3, J4, and J5). Communication between modules is accomplished by a 3-wire sensor bus. These 3 wires run in parallel from module to module. The J4 connector on the MBB also provides both power and communication directly to the Scrolling Marquee display. The J5

connector on the MBB provides a LEN interface at the field connection terminal (TB).

Yellow LED

The MBB has one yellow LED which is used to indicate CCN communication activity. The Carrier Comfort Network→ (CCN) LED will blink during times of network communication.

Communication Failures

If the Scrolling Marquee or Navigator display Communication Failure or the green or yellow LED’s do not flash on the boards then the problem could be the communication chip on one of the control boards (MBB, ECB or AUX1). Use an ohm meter to measure the resistance on the communication pins of the boards to determine if the board is bad. If the reading is less than half the value indicated in Table 7, then the board needs to be replaced.

Table 7 — LEN and CCN Communication Resistances

	Board Serial	(LEN) Resistance between Pins/			(CCN) Resistance between Pins/
Device			Connector			Connector
	Number
		Pins 1 to 3	Pins 1 to 2	Pins 2 to 3	Pins 5 to 7	Pins 5 to 6	Pins 6 to 7

	Prior to 4702N	15K Ω	7.5K Ω	7.5K Ω	15K Ω	7.5K Ω	7.5K Ω
		J3, J4, & J5	J3, J4, & J5	J3, J4, & J5	J5	J5	J5
MBB
	Starting 4702N	18.9K Ω	9.9K Ω	9.9K Ω	18.9K Ω	9.9K Ω	9.9K Ω

		J3, J4, & J5	J3, J4, & J5	J3, J4, & J5	J5	J5	J5

	Prior to 0803N	5.9K Ω	5.2K Ω	5K Ω	---	---	---
		J2	J2	J2
ECB
	Starting 0803N	18.9K Ω	9.9K Ω	9.9K Ω	---	---	---

		J2	J2	J2

AUX1	---	29K Ω	16K Ω	13.5K Ω	---	---	---
		J9	J9	J9

IMPORTANT: The resistive values should be read when the board is powered off and the unit is locked out.

48/50PD

Alarms and Alerts

Viewing and Clearing Unit Alarms

Presence of active alarms will be indicated on the Scrolling Marquee display by the Alarm Status light turning on and by the number of active alarms being displayed in the automatic View of Run Status. Presence of active alarms may also be signaled on the Alarm Output terminals. Each alarm may also be broadcast on the CCN network. Active alarms and past alarm history can be reviewed and cleared via the local display or a CCN device. The following menu locations are used for the local display:

Alarms→R.CURR (Reset All Current Alarms)

Change to YES to reset all active alarms. Turning unit power off will also reset all current alarms.

Alarms→R.HIST (Reset Alarm History)

Change to YES to reset the alarm history. Turning unit power off will not reset the alarm history.

Alarms→CURR (Currently Active Alarms)

Use the ENTER key, then scroll through any alarm numbers using the up and down arrow keys. Alarms are displayed in numerical order.

Alarms→HIST (Alarm History)

Use the ENTER key, then scroll through any alarm numbers using the up and down arrow keys. Up to 20 alarms are displayed in order of occurrence, with time and date.

The description for an alarm can be viewed on the Scrolling Marquee display by pressing ESCAPE and ENTER keys simultaneously while displaying the alarm code number. Be sure to expand description for each code, because in some cases there are different possible descriptions and causes for the same code number.

Diagnostic Alarm Codes and Possible Causes

Alert Code T051

There are 5 different texts for this alert code. There are three different alerts, two of which have corresponding test mode alerts indicated with “Service Test” in the expanded text. Pressing enter and esc on the marquee or navigator to expand the T051 alert will show you one of the below alerts. Make sure the expanded text is read correctly before troubleshooting.

SDigital Compressor Control Board Alarm

This alert occurs when the Digital Scroll Controller (DSC) energizes its alarm relay. Refer to the DSC’s LED diagnostic to determine which of the nine codes are present. Power cycle will

clear the DSC’s LED code. When the DSC’s alarm clears, this alert will automatically clear.

SCompressor A1 Safety Trip

This Alert indicates that Current Sensing A1 (CS.A1) has been enabled. The unit does not support the use of a current sensor at this time. Change the CS.A1 to disable and this alert will clear and not return.

(Configuration→COOL→CS.A1)

SCompressor A1 Current Detected After Turnoff

(Configuration→COOL→CS.A1)

Alert Code T064 - Circuit A Saturated Condensing Temperature Thermistor Failure

This alert occurs when the temperature is outside the range -40_to 240_F (-40_to 116_C). When this occurs, the control will use

48/50PD05 specifications

The Carrier 48/50PD05 is a remarkable addition to Carrier's lineup of rooftop units, offering advanced cooling and heating solutions for commercial applications. Designed for medium-sized buildings, this unit is well-suited for both new installations and as a replacement for older systems, thanks to its versatile features and efficient performance.

One of the standout features of the 48/50PD05 is its energy efficiency. It incorporates state-of-the-art technology to achieve high Seasonal Energy Efficiency Ratios (SEER) and EER ratings, reducing operational costs while delivering superior comfort. The unit is also compliant with the latest energy regulations, making it an environmentally friendly choice for building owners concerned about sustainability.

The 48/50PD05 is equipped with a highly efficient scroll compressor, which not only enhances performance but also contributes to quiet operation. This is a significant advantage in commercial spaces where noise levels need to be kept in check for comfort and productivity. Additionally, the unit includes advanced airflow design, ensuring even distribution of conditioned air throughout the space.

Technologically, the Carrier 48/50PD05 features Carrier's Infinity Control system, which allows for precise control of indoor climate. This intelligent control mechanism can be integrated with smart building management systems, enabling users to monitor and manage energy use effectively. Wi-Fi connectivity is also available, providing remote access for real-time adjustments and diagnostics.

Durability is another characteristic of the 48/50PD05. Constructed with high-quality materials, the unit withstands various environmental conditions, ensuring longevity and reliability. Moreover, the modular design facilitates easy maintenance, making service procedures efficient and cost-effective.

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Overall, the Carrier 48/50PD05 stands out as a high-performance HVAC solution that combines efficiency, technology, and durability. It provides building owners with a versatile tool to ensure comfort while minimizing their environmental footprint. With a strong emphasis on energy savings and advanced control features, this rooftop unit is a smart investment for any commercial property.