ABB Contactor Coil Testing: A16, A63-30, and Lennox AC Replacement

Check the coil first. That's the advice I give every buyer who asks about ABB contactors, and it's not because the main contacts don't matter. It's because coil failures are the most common reason a new contactor comes back dead on arrival. In my role as quality compliance manager at an industrial electrical distributor, I review about 200 incoming contactor lots a year. Roughly 40% of our returned contactors are coil-related—wrong coil voltage, open winding, or a coil that burns out in the first few hours. The model number can be right, the poles can be right, the amp rating can be right, and the contactor still won't pull in if the coil is wrong or damaged. This applies whether you're looking at an ABB A16 contactor, an ABB A63-30 contactor, or a generic 30 amp contactor 120 volt coil.

Before you trust that advice, you should know who's giving it. I'm not a design engineer. I'm the person who checks contactors before they ship to customers. Over the last four years, I've inspected thousands of ABB contactors across the A and AF series. I've rejected batches for mislabeled coils, and I've built our incoming inspection checklist from the failures we actually saw. In our Q1 2024 audit, 3 out of 14 coil failures were units where the printed label said 120V but the coil measured like a 24V coil. That's exactly why incoming inspection matters even for a brand with ABB's reputation.

The counterintuitive part is this: most buyers focus on the amp rating. The question everyone asks is 'how many amps is it?' The question they should ask is 'what's the coil voltage, and what does the application actually need?' A contactor that's undersized for the load won't last. But a contactor with the wrong coil won't start. So when someone asks me about a replacement contactor, I check the coil first—before I even look at the contact rating.

How to Test a Contactor Coil with a Multimeter

Here's the coil test we use on the bench. It won't replace the manufacturer's test procedure, but it catches most open windings and a lot of wrong-coil units.

1. Disconnect power and lock it out. This is not optional. Even for a resistance check, isolate the contactor and verify the circuit is dead with a test lamp or non-contact voltage tester.
2. Remove the coil wires from terminals A1 and A2. If the coil is still connected to the circuit, other components can give you a false reading.
3. Set the multimeter to resistance. Start with the 200Ω or 2kΩ range if you're not sure.
4. Measure across A1 and A2. Let the reading settle for a second or two.
5. Compare the reading to a known-good coil of the same model or the coil resistance in the ABB technical catalog. For a typical 120V ABB electromechanical coil, I usually see a reading in the hundreds of ohms. But the exact number depends on the coil design, and healthy coils can be outside that range. What I'm really looking for is OL, which means an open winding, or a reading that's essentially zero on a coil that should have measurable resistance. (A very low-resistance coil can read close to zero, so use the spec.)

That test will catch a completely open or shorted coil. It won't catch everything. It won't tell you if the pickup voltage is correct, whether the armature moves freely, or if the spring is weak. It also won't catch a coil that's partially shorted in a way that still reads sort of normal. And there's one big exception: ABB's AF line uses an electronic coil interface, so a simple ohm reading across A1-A2 can show OL or a diode-like reading even on a perfectly good coil. For AF contactors like the AF09 or AF96, don't rely on the old multimeter test—use the manufacturer's diagnostic guidance.

What I Check on an ABB A16 or A63-30 Contactor

When I inspect an ABB A16-30-10 or A63-30-10, I check four things in this order: the coil, the auxiliary contact, the main contacts, and the mechanical action.

• Coil. The label has to match the measured resistance, and the coil voltage has to match the circuit. On an ABB contactor, the coil terminals are A1 and A2. If the label is legible, verify the voltage and frequency before you install it.
• Auxiliary contact. The '-10' suffix means one normally open auxiliary contact. On most ABB contactors that's terminals 13 and 14. I check continuity at 13-14 with the contactor actuated, just to confirm the aux contact changes state.
• Main contacts. I look for pitting, welding, or embedded debris. Dark silver alloy is normal—it's oxidation, not burning. What I don't want to see is contact material that's actually been transferred or melted.
• Mechanical action. Press the armature down by hand. It should move smoothly and snap back when you release it. I learned this the hard way last year: a batch of coils read fine, but one unit had a cracked armature and would not pull in. It passed the ohmmeter test and failed in the panel. Now every sample gets the physical check too.

The model number itself tells you a lot. The 'A16' is the frame size and thermal rating, the '30' means three main poles, and the '10' means one built-in N/O auxiliary contact. On an A63-30-10, the '63' is the frame size, not a guarantee that it can carry 63 amps in every application. The actual rating depends on the utilization category under IEC 60947-4-1. A contactor rated 63A in AC-1 might be rated much lower in AC-3, which is the typical motor-load category. So when someone asks for a '30 amp contactor 120 volt coil,' my first question is: 30 amps in what category?

Replacing a Lennox AC Contactor

If you're searching for a Lennox AC contactor replacement, you're probably here because a condenser isn't running. Before you order anything, check the coil voltage on the old contactor. Some Lennox units use a 24V coil controlled by the thermostat circuit; others use a 120V coil. If the label is burned or missing, trace the wiring and use the unit's diagram. For a line-voltage circuit, you'll often be looking for a 30 amp contactor 120 volt coil—usually two-pole for a single-phase condenser. But that's not enough information to buy a replacement. You also need the right pole count, mounting dimensions, terminal style, and enclosure space.

An ABB A16-30-10 is not automatically a '30 amp contactor' in HVAC terms. Its AC-3 rating is 16A, and the allowed load depends on voltage and utilization category. If you're switching a 30A resistive load, a smaller contactor might work. If you're switching a 30A compressor, you need the AC-3 rating to back it up. The conservative move is to check the ABB catalog or talk to an authorized distributor before cross-referencing a Lennox part. In North America, also confirm the contactor is UL 508 listed for the application. We didn't have a formal cross-reference process until the second time a 'compatible' replacement arrived with the wrong terminal spacing. Now we verify dimensions before we recommend a substitute.

To be fair to ABB, their A line is solid. The failures I see are rarely mysterious. Most of them come down to the wrong coil being installed, a coil that was damaged by overvoltage, or mechanical damage during shipping. That's why I keep coming back to the coil test. It's the quickest check for the most common failure point, and it takes about two minutes.

Where This Advice Stops Being Useful

Testing the coil with a multimeter is a fast checkpoint, not a full acceptance test. It won't catch a cracked armature, a weak return spring, or a coil that picks up at 140V instead of 90V. It also won't tell you whether the contactor is correctly sized for the motor. If you're doing this for critical equipment, use the ABB technical documentation and, ideally, measure pickup and dropout voltage on a sample.

My experience is based on roughly 200 incoming lots per year, mostly IEC-rated ABB contactors in the A and AF series. If you're using a different manufacturer, the coil readings will be different. And if you're replacing a Lennox AC contactor in the field, this article is not a substitute for the unit's wiring diagram. The reliable sequence is simple: verify the coil voltage, verify the pole count, confirm the contact rating for your application, and then test the coil with a multimeter before you install it. It's the cheapest way to avoid a callback, and it's the difference between trusting a brand and actually verifying quality.