3W3 – HARD START KIT (3 WIRE, 4-5 TON)

If your compressor hesitates or trips the breaker on hot days, a hard start kit helps. The Supco 3W3 is a heavy-duty 3-wire kit with relay and start cap for large 4-5 ton compressors in bigger homes and commercial systems.

Specs: 3-wire, 4-5 ton, potential relay + start cap, Supco CSRU3

Replaces: 3W3, CSRU3

Fits: Single-phase compressors in 4-5 ton AC and heat pump systems. All major brands.

Need help? See our AC Not Cooling Troubleshooting Guide or Capacitor Cross-Reference Chart.

In stock at Open To Public HVAC Parts in Dallas. We test parts at the counter before you buy. Call or text (214) 340-9421.

Specs

• TypeCompressor hard start kit
• Capacity range4 to 5 ton
• Type3-wire, potential relay
• FunctionBoosts starting torque, drops out once running
• Before fittingMeter the compressor - if it trips the breaker instantly the windings are shorted or grounded and a kit will not help

Cross-reference numbers

This part replaces the following OEM and aftermarket numbers:

• CSRU3

Not sure if your number matches? Call (214) 340-9421 or bring the old part in — bench-testing is free.

What does a hard start kit actually do?

It adds a start capacitor and a relay that briefly boost the compressor's starting torque, then drop out once it is running. It helps a compressor that turns but struggles to break away.

When does one genuinely help?

A compressor that starts slowly or noisily, one that hums and then goes, long line sets, low or sagging incoming voltage, and units that trip the OVERLOAD on start-up. If the compressor gets going but has a hard time doing it, that is the case a kit is for.

When will a hard start kit NOT help?

If the compressor is electrically failed - windings shorted together or grounded to the shell - it will trip the breaker instantly and never start at all. No hard start kit fixes that, and one will not get you through the weekend either. Same with an open winding: nothing happens, and a kit adds nothing. Meter the compressor first. If it trips the breaker the moment it calls, you are looking at a compressor, not a start kit.

So what is the band-aid case?

A compressor that is mechanically tight or worn - it draws locked-rotor current, groans, and trips the internal overload rather than the breaker. A kit will often push it through and buy you time. That is real, useful time, but understand the compressor is on its way out.

Two-wire or three-wire?

Two-wire kits wire across the run capacitor and are quick to fit. Three-wire kits use a separate potential relay and are the more precise, more durable option. Match the kit to the tonnage of the unit.

Will it hurt anything to add one?

On a healthy system it adds a component that can fail on its own. Fit one because there is a starting problem to solve, not as routine maintenance.

Can you test my start components?

Bring the capacitor in and we will meter it free at the counter. 10226 Plano Rd, Suite 104 in Dallas.