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HVAC Controls - Compressor Time Delay Relays

Compressor time delay relays are low-voltage-controlled timers on the outdoor condenser that prevent compressor short-cycling.

Short-cycling occurs when the outdoor unit's compressor shuts off and tries to start before the system's refrigerant pressures equalize (when both suction and discharge pressures are the same psi). There are several reasons a compressor would short-cycle; the most common being indoor temperature fluctuations. This means the thermostat is calling for cooling or heating too soon between run times. Imagine what would happen to your vehicle's engine if at every red stop light you turned it completely off, and when the light turned green, you restarted it again. This is what a short-cycling compressor is experiencing.

Other reasons why a system would short-cycle include; an undersized or oversized system, the system is not performing properly (e.g. air filters dirty, low refrigerant levels, etc.), extreme indoor temperature changes (cooling down then heating up or vice versa), or even the little one playing with the thermostat are reasons for a compressor to short-cycle.

Newer systems have time delays that are factory installed in the condenser (outdoor unit). Older systems or basic models may not contain a compressor time delay.

These little controls can be the "saving grace" for the compressor from internal damage. Compressor time delay relays should be added for extra protection, or when an existing unit needs that extra "relief" between run times.

There are several different types of compressor time delay relays on the market. Most of your common time delays are wired in series with the low-voltage control wiring and activate "on make" or "on break".

"On break" means that the delay timer activates when the unit shuts off. "On make" means the delay timer activates when the unit calls for heating or cooling. Most of your compressor time delay relays have switches to set the delay time in seconds or minutes. Some relays have a fixed delay time. The most common delay setting for a residential system is 5-10 minutes.

Heating and Air Conditioning Controls Online

Go to Alps ControlsAlps Controls linkAlps Controls:AlpsControls.com is the world's largest online marketplace for HVAC and building automation control parts and peripherals.
– https://www.alpscontrols.com
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Go to Controls CentralControls Central linkControls Central:ControlsCentral.com is the primary destination for controls and HVAC products for contractors and qualified commercial end-users. We offer a wide range of valves, combustion controls, relays, thermostats, pressure controls, temperature sensors, and other products from leading manufacturers such as Honeywell, Johnson Controls, Belimo, Fireye, Functional Devices, Siemens.
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Go to Delta ControlsDelta Controls linkDelta Controls:Delta Controls offers complete HVAC system solutions with easy-to-use HVAC controls for large central plants to zone terminal units and sensors.
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Go to Distech ControlsDistech Controls linkDistech Controls:The Distech Controls HVAC controls are designed for dependable long-term performance. Come here to find out more about our BACnet and LONWORKS controllers.
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Go ICM ControlsICM Controls linkICM Controls:Find heating controls, furnace controls, voltage monitors, and a variety of HVACR electronic controls from ICM Controls an American manufacturer of electronic controls.
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Go to Johnstone SupplyJohnstone Supply linkJohnstone Supply:HVAC/R Controls | Johnstone Supply | Wholesale Distributor to the HVAC, Refrigeration and Property Maintenance Industries
– https://www.johnstonesupply.com/storefront/hvacr-parts/controls
Go to NECCNECC linkNECC:NECC is an Authorized Distributor for HVAC controls manufacturers such as Honeywell, Johnson Controls, Belimo, Siemens, Barber Colman, KMC, Erie, with over 50 HVAC OEMs in our line card.
– https://necc-controls.com/product-lines
Go to TraneTrane linkTrane:Tracer Controls | Trane Commercial
– https://www.trane.com/commercial
Klein Tools - Electrical Tester
The links on this page will take you to HVAC controls online.
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By Category: HVAC Equipment Controls

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Heating and AC Controls:
Terms & Online References

Sensors
Time Delays
Timers
Temperature High / Low
Ambient Controls
Compressor
Ignition / Flame
Pressures High / Low
Thermostats
Valves
Solenoids
Refrigerant
Defrost
Zone / Zoning / Dampers
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Digital Thermometer Dual Channel Thermometer
Orbit Thermostat