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HVAC Relay and Controls
HVAC Relays and Controls for Compressor and Equipment Protection
ATC Diversified Electronics offers a range of HVAC relays and controls designed to protect compressors, motors, fans, pumps, and other electrically operated HVAC equipment. Available solutions include compressor protectors, short-cycle timers, phase and voltage monitors, current monitoring relays, alternating relays, and advanced motor-monitoring products.
These controls help HVAC systems respond to conditions such as phase loss, phase reversal, under-voltage, over-voltage, current changes, thermostat interruptions, and rapid compressor cycling. Depending on the product, ATC controls can monitor incoming electrical conditions, delay equipment restart after an interruption, alternate loads, or provide a relay response when operating conditions move outside established limits.
From compact short-cycle protection for individual compressors to three-phase monitoring and load-alternation controls for larger commercial and industrial HVAC systems, ATC provides multiple approaches for matching protection and control functions to the electrical requirements of the application.
Why Choose ATC HVAC Controls?
Compressor Short-Cycle Protection: ATC delay-on-break and delay-on-make timers can prevent a compressor from restarting immediately following a thermostat or power interruption, allowing a defined delay before operation resumes.
Three-Phase Monitoring: Selected HVAC controls monitor conditions such as phase loss, phase reversal, under-voltage, over-voltage, and phase unbalance to support protection of three-phase compressors and motors.
Single-Phase Voltage Protection: The CV Series combines under-voltage and over-voltage monitoring with short-cycle protection for compatible single-phase equipment and appliances.
Current Monitoring: ATC current-monitoring relays can detect the presence of AC current or monitor for over-current, under-current, or current-window conditions depending on the selected device.
Load Alternation: Duplex alternating relays can alternate two HVAC loads to help distribute operating time between compressors, pumps, fans, or other redundant equipment.
Multiple Restart Strategies: Delay-on-make and delay-on-break options allow the restart sequence to be matched to the requirements of the HVAC control circuit and compressor.
Short-Cycle Protection for HVAC Compressors
Rapid compressor restarting can occur when power or a thermostat signal is interrupted and quickly restored. ATC short-cycle protection timers introduce a controlled delay before the compressor is permitted to restart.
Delay-on-break products such as the AC-503, AC-505-5, and ASC-500 begin the protection period when a voltage or thermostat interruption occurs. The AC-800 delay-on-make timer begins its restart delay after power returns. This provides engineers with different timing approaches for matching compressor protection to the HVAC control sequence.
Phase, Voltage and Current Monitoring for HVAC Systems
Electrical conditions can affect compressor and motor operation before the problem is visible at the mechanical equipment. ATC offers phase monitors, voltage monitors, and current-monitoring relays that can be incorporated into HVAC control systems to detect abnormal electrical conditions and provide a control-relay response.
The AC-301 and AC-302 monitor three-phase power for conditions including phase loss, under-voltage, phase reversal, power failure, and thermostat interruptions while also incorporating restart timing. Other products, including the SLA and SLU-100 Series, provide additional three-phase monitoring options for HVAC motors and compressors.
Find the Right HVAC Relay or Control
Selecting the right HVAC control relay, compressor protector, short-cycle timer, or phase monitor depends on the equipment voltage, single- or three-phase power, monitored fault conditions, required restart delay, control voltage, current-monitoring requirements, number of loads, and the desired reset and relay behavior.
Explore the ATC HVAC controls above to compare compressor protection, time-delay, current-monitoring, voltage-monitoring, phase-monitoring, and load-alternation options. ATC Diversified Electronics can also assist with selecting controls for commercial and industrial HVAC equipment, compressors, motors, pumps, and multi-unit systems.
HVAC Relay and Control FAQs
What are HVAC control relays?
HVAC control relays are electrical control devices used to monitor, switch, delay, or protect equipment such as compressors, motors, fans, and pumps. Depending on the device, an HVAC relay may respond to voltage, phase, current, thermostat, timing, or load-control conditions.
What is compressor short-cycle protection?
Compressor short-cycle protection prevents a compressor from restarting immediately after a power or thermostat interruption. A time delay holds the compressor off for a defined period before allowing another start, helping prevent rapid stop-start operation.
What is the difference between delay-on-make and delay-on-break for HVAC compressors?
A delay-on-make timer begins its delay when power is applied or restored and prevents the compressor from starting until the delay expires. A delay-on-break timer begins its protection period when the control voltage or thermostat circuit is interrupted. The appropriate method depends on the HVAC control sequence.
What does the ATC AC-800 Delay-On-Make Timer do?
The AC-800 provides compressor short-cycle protection by delaying restart after a voltage or control-circuit interruption. Its adjustable delay can also help stagger compressor restarts in installations containing multiple HVAC units.
What conditions does the AC 2020 Compressor Protector monitor?
The ATC AC 2020 Compressor Protector is designed to protect against phase loss, under-voltage, over-voltage, phase reversal, and short cycling. It also provides selectable time delays, automatic or manual reset options, fault indicators, and last-fault memory.
What do the AC-301 and AC-302 HVAC controls monitor?
The AC-301 and AC-302 monitor three-phase power for phase loss, under-voltage, phase reversal, power failure, and thermostat interruptions. The AC-301 uses an adjustable restart on-delay, while the AC-302 uses an adjustable off-delay before allowing the control relay to re-energize.
Why use a phase monitor on HVAC equipment?
A phase monitor can detect abnormal three-phase conditions before allowing or continuing operation of a compressor or motor. Depending on the model, monitored conditions can include phase loss, phase reversal, under-voltage, over-voltage, and phase unbalance.
Can ATC monitor single-phase HVAC voltage?
Yes. The ATC CV Series monitors single-phase under-voltage and over-voltage conditions and incorporates a selectable short-cycle protection delay for compatible air conditioners, refrigeration equipment, and other single-phase loads.
What is an HVAC current monitoring relay?
A current monitoring relay detects electrical current in a monitored conductor or compares current with defined operating thresholds. This can provide a control signal when equipment starts, stops, draws excessive current, or falls below an expected current level.
Does ATC offer self-powered AC current monitors?
Yes. The CMG Series detects AC current using a conductor passed through its integrated current transformer. The monitor is magnetically coupled to the conductor and does not require a separate supply voltage to operate.
What does the CMU100USD current monitoring relay do?
The CMU100USD is a DIN rail-mounted multifunction AC current monitoring relay that supports over-current, under-current, and current-window monitoring. It also provides automatic or manual reset options and can use an external current transformer to extend the monitored range.
Why use an alternating relay in an HVAC system?
An alternating relay switches operation between two loads so operating time can be distributed between them. In HVAC applications, this can be useful for systems with two compressors, pumps, fans, or other redundant loads that should alternate between operating cycles.
What is the ATC Duplexor?
The Duplexor is an alternating relay designed to alternate two loads each time its control switch changes state. The ARA Series provides automatic alternating operation, while the ARB Series adds the ability to lock the relay into a selected load sequence.
How do I choose the right HVAC control relay?
Consider whether the equipment is single phase or three phase, system and control voltage, compressor restart requirements, monitored voltage or current conditions, number of controlled loads, relay contact requirements, reset method, installation format, and the specific faults or operating conditions the control must detect.