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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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– 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
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