AC not turning on at all? The contactor is one of the first things we check
The contactor is the high-voltage switch that sends power to your outdoor unit every time the thermostat calls for cooling. When it fails the system goes completely dead — no fan, no compressor, nothing. Here’s what it does, why it burns out, and what we charge to replace it.
- Flat-rate price — $240, confirmed before we start
- Usually diagnosed and replaced same visit
- 5-year warranty on every replacement
- Clubb 33 members pay $0
The contactor is an electrically operated switch
A contactor is essentially a heavy-duty relay. Like all relays, it uses a small-voltage control circuit to switch a much larger-voltage load circuit — allowing a low-voltage signal from the thermostat to safely open and close a 240V circuit that powers your compressor and condenser fan motor. That principle is what makes automatic control possible: without contactors and relays, you’d have to manually switch your AC on and off at the outdoor unit every time the thermostat called for cooling.
The main components of a contactor are a coil and a set of electrical contacts. When the thermostat calls for cooling, it sends a 24-volt signal through the Y wire to one side of the contactor coil. That low-voltage current energizes the coil, creating a magnetic field that pulls a metal plunger downward — physically closing the contact points. Once the contact points are closed, 240V line voltage flows from the disconnect through the contactor to the compressor and condenser fan motor, and the system starts. When the thermostat is satisfied, the 24V signal drops, the coil de-energizes, the magnetic field collapses, and a spring pushes the plunger back up — opening the contacts and cutting power to the outdoor unit.
Contactors are specifically designed to handle the inductive loads found in HVAC equipment — compressors and motors that draw a significant spike of locked-rotor current at startup before settling into their running amperage. This is different from resistive loads like heating elements, which is why contactor amperage ratings specify separate FLA (full load amps) ratings for inductive loads and higher RES ratings for resistive loads.
Single-Pole, Two-Pole, and Three-Pole Contactors
The pole count tells you how many legs of high-voltage power the contactor switches when it opens and closes. Here’s what each type does and where you’ll find it.
Single-Pole Contactor
Switches one leg of 240V power — leaves the other always connected
How it switches power:
A single-pole contactor only opens and closes one side (L1) of the 240V supply to the compressor. The other leg (L2) runs directly through the contactor terminal without being switched — it is always connected to the compressor whether the system is on or off. This design is simpler and was the standard on many older residential systems.
Typically found on:
- Many older residential split systems
- Some package units
• Systems without crankcase heaters on certain configurations
Two-Pole Contactor
Switches both legs of 240V power — fully isolates the compressor when open
How it switches power:
A two-pole contactor switches both L1 and L2 simultaneously — when the contacts open, both legs of the 240V supply are interrupted and the compressor is completely isolated from line voltage. This is the most common contactor type in modern residential HVAC and provides a true disconnect for the outdoor unit every time the system cycles off.
Typically found on:
- The majority of modern residential split systems
- Most package units produced in the last 20 years
• The most common contactor type we replace in Las Vegas
Three-Pole Contactor
Switches all three legs — used on three-phase equipment
How it switches power:
A three-pole contactor switches all three legs of three-phase power simultaneously. Three-phase power is not common in residential homes but is standard in commercial and light commercial HVAC equipment — larger rooftop units, commercial condensing units, and some large package equipment.
Typically found on:
- Commercial and light commercial HVAC equipment
- Three-phase condensing units and rooftop systems
• Larger package units in commercial applications
Which type does my system have?
Most Las Vegas homes have a two-pole contactor. Older systems may have a single-pole. Three-pole is uncommon in residential — it's primarily a commercial part. Your technician identifies the correct replacement from the existing unit's wiring before anything is removed.
How and Why Contactors Fail
Every time your AC system turns on, the contactor closes. Every time it turns off, the contacts open. In Las Vegas — where systems cycle repeatedly across a 14-hour day in summer — that adds up to thousands of on/off cycles per season. Each cycle creates a small electrical arc as the contacts close and open under load. Over time, that arc burns and pits the contact surfaces.
| How it fails | What's actually happening |
|---|---|
| Contact pitting and burning | Every time the contactor closes under load, a small electrical arc forms at the contact surfaces. That arc is energetic enough to vaporize tiny amounts of the contact metal over time, leaving pits and craters in the contact surface. Pitted contacts create resistance — and resistance across the contactor means a voltage drop that reduces the voltage reaching the compressor. A compressor running below rated voltage draws more current, runs hotter, and wears out faster. |
| Contact welding | In some failure modes, especially after a severe power event or repeated hard starts, the contacts can weld together in the closed position. A welded contactor stays closed even when the thermostat is not calling for cooling — the compressor runs continuously and won't shut off when the thermostat is satisfied. This is a serious failure that can quickly damage the compressor. |
| Coil failure | The contactor coil — the electromagnet that pulls the plunger closed — can fail if it overheats or experiences a voltage spike. A failed coil won't energize when the thermostat sends a 24V signal, so the contacts never close and the system never starts. Coil failure causes the same symptom as a completely dead system. |
| Insect contamination | Las Vegas outdoor units attract insects — particularly fire ants — that nest inside the control panel and contactor housing. Insects bridging the contact points cause erratic operation, false startups, or complete failure. We see this regularly on service calls that initially look like a failed contactor but are actually a contamination issue. |
| Spring fatigue | The return spring that pulls the plunger back up when the coil de-energizes can weaken over time. A fatigued spring allows the contacts to partially stick in the closed position, causing the system to run when it shouldn't or to not fully open the circuit when it should. |
Signs Your Contactor Has Failed
| What you notice | What it likely means |
|---|---|
| Outdoor unit completely won't start | The thermostat calls for cooling, the indoor blower runs, but nothing happens outside. No fan, no compressor hum — total silence. This is the most common sign of a failed contactor coil or contacts stuck open. |
| System won't shut off | The thermostat is satisfied and has stopped calling for cooling, but the outdoor unit keeps running. Contacts may be welded closed. Turn the system off at the thermostat and call us — a compressor running continuously without the thermostat calling for it needs immediate attention. |
| Outdoor unit starts then immediately stops | The contactor closes briefly then opens — possibly due to a coil that's intermittently failing, or contacts that close poorly and trip a protection device. |
| Visible burn marks or pitting | If you look inside the outdoor cabinet (with power off), a severely pitted or burned contactor is sometimes visible. Black marks on the contacts or surrounding area indicate significant arcing. |
| Chattering or buzzing from the outdoor unit | A contactor that's trying to close but can't hold closed makes an audible chattering sound. This usually indicates a coil problem — the coil is energizing but not developing enough magnetic force to hold the plunger down, possibly due to low control voltage or a weakening coil. |
One Las Vegas summer without Clubb 33 can cost more than two years of membership.
STANDARD
-
5-year warranty
-
Single, two-pole, or three-pole — same price
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Full system check after replacement
CLUBB 33
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5-year warranty
-
Single, two-pole, or three-pole — same price
-
Full system check after replacement
Clubb 33 — $33/month. Contactor replacement is $0 for members.
$3,000 repair credit per visit. Covers the full $240 contactor replacement and then some. Join at VegasAC.com/clubb-33
What the Technician Does on a Contactor Call
We don’t just pull the old contactor and put a new one in. Every replacement includes a complete inspection and verification process.
| Step | What we do | |
|---|---|---|
| 1 | Disconnect power | The outdoor disconnect is pulled before opening the cabinet. The capacitor is discharged. No work starts on live high-voltage equipment. |
| 2 | Visual inspection of existing contactor | We inspect the contact surfaces for pitting, burning, or welding. We check for insect contamination. We look at the coil leads for signs of heat damage or failed insulation. |
| 3 | Control voltage check | We verify that 24V is being delivered to the contactor coil from the thermostat when the system calls for cooling. If control voltage is absent, a contactor swap won't fix the problem — we diagnose further upstream. |
| 4 | Confirm pole count and amperage rating | The replacement must match the original's pole configuration and be rated for the amperage of the equipment. We match the replacement to the original's specifications — we never install a contactor rated below the system's requirements. |
| 5 | Install and verify | The new contactor is installed with all wires connected to the correct terminals. On two-pole replacements especially, we verify the wiring is correct for the specific system — some crankcase heater and heat pump configurations require specific attention to how L1 and L2 are wired through the contactor. |
| 6 | System startup and amperage check | We restart the system, measure compressor and fan motor amperage, and confirm both are within their rated operating range. We also measure voltage across the new contactor under load to confirm no significant voltage drop. |
We always check the capacitor on a contactor call.
A pitted or failing contactor can cause compressor hard starts that stress the capacitor. We test the capacitor reading on every contactor replacement — if it's within 10% of rated we leave it, if not we recommend replacing it while we're already there. One call, complete job.
Frequently Asked Questions
How do I know if it's the contactor or the capacitor?
Both can cause the outdoor unit to not start. The difference: a failed capacitor usually causes the compressor to hum without starting — you can hear it trying. A failed contactor is typically complete silence — nothing even attempts to start. A failed coil on the contactor also produces silence. Your technician will test both before recommending anything. Sometimes it's the capacitor, which at $250 is slightly more than a contactor at $240. Either way you're looking at a same-visit repair.
Does the pole count affect the price?
No. Single-pole, two-pole, and three-pole contactors are all $240 at Orange Air. The pole count affects which part goes in, not what you pay. We carry all three types on the truck.
My system won't shut off — is that the contactor?
It can be. A contactor with contacts welded in the closed position will keep running the compressor even when the thermostat stops calling for cooling. If your outdoor unit is running when you don't expect it to be, set the thermostat to OFF — not just a higher temperature, but OFF — and call us. A compressor running continuously without a thermostat call can overheat quickly.
Can a bad contactor damage my compressor?
Yes, in two ways. First, a contactor with pitted contacts creates a voltage drop — the compressor receives less than the rated voltage and draws more current to compensate, running hotter and wearing out faster. Second, a welded contactor that keeps the compressor running continuously without proper off-cycle rest will cause overheating. Either situation can shorten compressor life significantly. Catching and replacing a pitted contactor is one of the highest-value repairs in residential HVAC.
How long does a contactor replacement take?
Most contactor replacements are completed in under an hour, including the full inspection, replacement, and system verification. We carry single-pole, two-pole, and three-pole contactors on every truck.
Is a contactor replacement worth it on an older system?
Almost always. A contactor at $240 is one of the most cost-effective repairs in residential HVAC. As long as the compressor and coils are in reasonable condition, replacing a failed contactor is the right call. We'll tell you if the overall system condition changes that equation — we're repair-first and we'll give you an honest assessment.
AC not turning on? Call or text now
702-604-8092
We carry single-pole, two-pole, and three-pole contactors on every truck. Most replacements are diagnosed and completed same visit. $240 flat-rate — price confirmed before we start.