If a Y2 (or Y2_SPT) call begins while the unit was under “Y1 cooling” control, compressor no. 2 will not be started until “Y1 cooling” control has ended.

If the Y2 (or Y2_SPT) call ends, with compressor 1 in an unloaded state and compressor 2 ON, then compressor 1 will be immediately brought up to the fully loaded state. If however, the Y2 (or Y2_SPT) call ends, with compressor 1 in an unload- ed state and compressor 2 OFF, then compressor 1 will be left in its unloaded state. In either case the compressor 1 will be loaded/unloaded as appropriate to the “Y1 Low Limit”.

The control shall lockout compressors if SAT becomes too low and an alarm shall be issued.

Compressor no. 1 lockout at SAT < 53 F. Compressor no. 2 lockout at SAT < 48 F.

If SAT sensor fails the control will energize compressor no. 1 fully loaded (unloaders off), whenever there is a Y1 (or Y1_SPT) call. Compressor no. 2 will be energized whenever there is a call for Y2 (or Y2_SPT).

NOTE: When a VAV unit with software version 4.0 and later is configured to operate from a space thermostat (VVT® relay pack) or a space sensor, compressors start loaded and then unload as needed. This is the opposite of the normal VAV unloading sequence. When operating from supply-air tempera- ture (SAT) sensor, VAV units will unload in the reverse sequence.

FIELD TEST — The field test program is initiated by moving up DIP switch no. 4 to the OPEN position. The outdoor-air damper will close. The control allows 90 seconds for the damp- er to close in case it was in the full open position. Next, the indoor-fan contactor will be energized, and the outside-air damper will begin to open to its default value of 20% and stay at that position for a short period of time. The outdoor-air damper will then open to its full open position and stay at that position for a short period of time. The outdoor-air damper will then close.

If the unit is equipped with power exhaust, stage 1 will be energized for 5 seconds. If the unit is configured for stage 2 of power exhaust, stage 2 will be energized for 5 seconds after the first stage is deenergized.

The first stage of heat will be energized for 30 seconds, after which the second stage heat will be energized for an additional 30 seconds. Heat is then deenergized.

The last step is the Cooling mode. Outdoor-fan contactor no. 1 is energized. This is followed by each stage of cooling energized with a 10-second delay between stages. After this is complete, outdoor-fan contactor no. 2 is energized for 10 seconds.

The compressors will now deenergize, followed by the out- door-fan contactors and indoor-fan contactors. If the unit is equipped with the Integrated Gas Control (IGC) board, the in- door fan will continue to operate for an additional 30 seconds after deenergizing the circuit.

The field test is then complete.

SERVICE

Before performing service or maintenance operations on unit, turn off main power switch to unit. Electrical shock could cause personal injury.

Service Access — All unit components can be reached through clearly labelled hinged access doors. These doors are not equipped with tiebacks, so if heavy duty servicing is need- ed, either remove them or prop them open to prevent accidental closure.

Each door is held closed with 3 latches. The latches are se- cured to the unit with a single 1/4-in. - 20 x 1/2-in. long bolt. See Fig. 63.

To open, loosen the latch bolt using a 7/16-in. wrench. Pivot the latch so it is not in contact with the door. Open the door. To shut, reverse the above procedure.

NOTE: Disassembly of the top cover may be required under special service circumstances. It is very important that the ori- entation and position of the top cover be marked on the unit prior to disassembly. This will allow proper replacement of the top cover onto the unit and prevent rainwater from leaking into the unit.

IMPORTANT: After servicing is completed, make sure door is closed and relatched properly, and that the latches are tight. Failure to do so can result in water leakage into the evaporator section of the unit.

Cleaning — Inspect unit interior at beginning of each heat- ing and cooling season and as operating conditions require. Remove unit side panels and/or open doors for access to unit interior.

MAIN BURNERS — At the beginning of each heating sea- son, inspect for deterioration or blockage due to corrosion or other causes. Observe the main burner flames and adjust if nec- essary. Check spark gap. See Fig. 64. Refer to Main Burners section on page 94.

FLUE GAS PASSAGEWAYS — The flue collector box and heat exchanger cells may be inspected by removing gas section access panel (Fig. 5-16), flue box cover, collector box, and main burner assembly (Fig. 65 and 66). Refer to Main Burners section on page 94 for burner removal sequence. If cleaning is required, clean all parts with a wire brush. Reassemble using new high-temperature insulation for sealing.

COMBUSTION-AIR BLOWER — Clean periodically to as- sure proper airflow and heating efficiency. Inspect blower wheel every fall and periodically during heating season. For the first heating season, inspect blower wheel bi-monthly to deter- mine proper cleaning frequency.

Fig. 63 — Door Latch

Fig. 64 — Spark Gap Adjustment

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Carrier 48EY024-068, 48EW, 48AW, 48AY020-060, 48EK, 48AK, 48AJ, 48EJ specifications Service
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48EJ, 48AJ, 48AK, 48EK, 48AY020-060 specifications

The Carrier 48EJ, 48AW, 48EK, 48AJ, and 48EY024-068 are cutting-edge rooftop air conditioning units designed for commercial applications. These models are renowned for their reliability, energy efficiency, and innovative technologies aimed at providing optimal indoor comfort.

One of the standout features of these units is their advanced cooling and heating capabilities. They employ a multi-stage compressor system that allows for precise temperature control, accommodating various load requirements. This flexibility is particularly beneficial in commercial settings where the cooling load can fluctuate throughout the day.

Energy efficiency is paramount in today’s environmental landscape, and Carrier has ensured that these models meet stringent efficiency standards. They incorporate high-efficiency scroll compressors, which significantly reduce energy consumption while delivering powerful performance. The units are also equipped with variable speed fans that adjust airflow based on demand, further optimizing energy use.

In terms of construction, these rooftop units feature a robust design that enhances durability and longevity. The cabinet is constructed to withstand harsh weather conditions, ensuring reliable performance year-round. Additionally, the units are equipped with corrosion-resistant coatings, particularly useful in coastal environments where salt exposure can be a concern.

The Carrier 48EJ, 48AW, 48EK, 48AJ, and 48EY models utilize advanced controls and connectivity features, allowing for easy integration into building management systems. This connectivity enables remote monitoring and control, facilitating quick response to changing conditions and simplifying maintenance tasks.

Noise reduction is another key characteristic of these models. They are designed with sound-absorbing insulation and low-noise fan blades to ensure quiet operation, making them suitable for noise-sensitive environments such as schools and hospitals.

These units are also available with various options for air filtration and dehumidification. The use of high-efficiency air filters enhances indoor air quality by trapping dust, pollen, and other airborne particles. Enhanced dehumidification capabilities ensure that spaces remain comfortable even in humid conditions.

In conclusion, the Carrier 48EJ, 48AW, 48EK, 48AJ, and 48EY024-068 rooftop units are engineered to offer exceptional performance, energy efficiency, and durability. With their advanced technologies and user-friendly features, they stand out as reliable solutions for meeting diverse commercial cooling and heating needs, making them a popular choice for many businesses.
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