Electric motor doesn't start - likely problems?

My central A/C air handler stopped working. The fan motor is a 220V single phase, capacitor start. The motor gets hot, the capacitor stays cool. The fan turns freely when pushed by hand, but pushing it does not get the motor running.

What are the most likely problems?


It sounds like the start winding is opened but I think you should be able to get it to start by spinning the rotor (with power applied of course) if that were the case. I work on DC and three-phase motors so I’m a bit out of my element with single-phase but there used to be centrifugal switches to disconnect the start winding once the motor is at speed. Those can fail and keep the start winding in too long and burn the winding or the capacitor.

Can you give more info from the nameplate? Manufacturer, etc. It ould be nice to know whether the capacitor stays in the circuit or is disconnected on this one in normal operation. Also there may be a thermal overload that has tripped or failed.

Your A/C “handler”. Do you mean the compressor cooling fan or the blower that moves the air in the house? The compressor cooling fan isn’t usually connected directly to the compressor. If the compressor isn’t turning then I would start with the relay that turns it on.

I assume you are talking about the condencer fan motor. If you can spin it by hand and it does not keep turnning there is a good chance that the motor has a major issue.

You need to call a pro.

I’m not a HVAC person but I just gutted a bunch of A/C units for scrap and the cooling fans were 110 volt.

Most cooling fans are 110. But condencer fans quite often ater 220.

If it is 220 V it is 2 phase. I would check all breakers or fuses. and then call a Pro like already advised if it is anything more than that.

You didn’t say whether the compressor runs. Does it? Because that takes us in another diagnostic direction.

If the compressor will run it indicates that the fuses are good and there is 220V present. (Do NOT let the compressor run for any length of time without the condensing fan motor)

If neither the compressor or the fan on top are running check the fuses first to make sure that 220V is present. You’ll need a meter for that.

If the breakers and fuses are good (the fuses will be in the disconnect box outside next to the unit) than I’d be looking at the capacitor.

You see, fans go bad. Compressors go bad. But they rarely go bad together. If neither is running you likely have a voltage problem or a bad capacitor. Here is a picture of a “dual” capacitor:

Notice that top of the capacitor is slightly recessed and absolutely flat. Look at your cap. If it is “swollen” on top or bulging it is a certainty that the cap is bad----and the likely source of the problem.

If it’s bad, don’t try to replace it without getting direction from us.

One last thing. Even if the compressor will run, you may still have a bad cap. On dual caps, sometimes only one side of the cap goes bad-----letting the compressor run but not the fan. It’s low hanging fruit, but it’s really common low hanging fruit: visually inspect the cap.

They appear to be, but they are always 220V. (in the US anyway)

That said, someone is bound to post a hyperlink with a 110V condensing fan. But in 20 years I can’t remember seeing one and I see thousands of them.

If neither the fan or compressor run, it is possible that the ‘relay’ is bad. (although in these applications they use a definite purpose contactor)

Both the compressor and fan will route through the **same **contactor. We see bad contactors often enough to keep them on our trucks, but a more common cause is blown fuses (not to be confused with the fuses or breakers in the main electrical panel) or bad capacitors.

Contactors are pretty reliable devices.

My guess with the very little information we’ve been given: a bad cap.

By contactor do you mean relay? Mine sticks about once every 2 years.

If it’s the contactor in the outdoor unit, and it looks anything like this: http://www.supplierlist.com/photo_images/12196/HLC-2X_Series_Definite_Purpose_Contactors_.jpg than it acts like a relay, but it is called a contactor.

If yours is sticking it needs to be replaced. The contacts have been burned enough through repeated use that they are “fusing” together under load.

This can cause more damage down the road. When we see the contacts charred/burnt we replace the contactor as a preventive measure.

ETA: As a point of reference, we probably change 25 capacitors for every contactor we change. (give or take: I’m not certain of the exact ratio)

NO there are very few 2 phase motors out there. 2 Phase power is a very strange and rare thing.

I think mine sticks because of corrosion but I’ll get my HVAC buddy to swap it out. the Ford museum might be interested in it.

If it’s the contactor than wacking it with a piece of wood may bring it back online and that would be a clear indication of what to replace. If nothing else, it will allow some frustration to be vented.

The air handler is the inside unit; i.e., the evaporator. This is the fan that circulates air through the house. It is definitely 220volt, 1 phase. And while I haven’t checked for power, the fact that the motor is getting hot is a pretty good indication that it’s getting it (also, I could hear a hum coming from the motor until I shut the breaker off).

Here’s the info from the plate:

Emerson K55HXEKD-7575
208-230 Volts
825 RPM
3 speed
PT #34K7601
1/3 HP

Note that while it is a 3 speed motor, only the common and high speed terminals are connected (plus the capacitor, of course).

If it is the indoor fan than there are 2 likely causes, in order of likeliness:

1) A bad cap. If the motor is hot (and the wheel will spin freely by hand, indication that it’s not bound up) than it is likely that 220V is being applied. If it is the capacitor on the indoor blower, it will not bulge----but can be bad all the same.

2) A bad motor Sometimes bad things happen to good motors. :wink:

The fact that the motor is hot suggests that the windings are not open, and that the cap is the problem.

If you want to try this and avoid a tech visit, replace the cap. The other thing you can try (with the power off, of course) is to switch the motor leads. Take one of the leads not being used and put it where the one that is being used is; IOW, switch fan speeds.

Awesome response, thanks. I will try switching the leads. If not, where do I find a replacement capacitor? I assume it’s not the sort of thing Lowes would carry. Would an electrical supply store have it, or would I have to seek out a place that specializes in motors?

A small motor repair shop, or an HVAC or appliance repair wholesaler mostly.

The old cap will have 2 pieces of info, as an example, 10uf @370 VAC or something like that. Your unit will likely have a 7.5, 10 or 15 uf (some have 12.5) and either 370 VAC or 440 VAC.

You can use a larger voltage rating—like use a 440 VAC instead of a 370 VAC; you just shouldn’t use a smaller one, a 370 VAC instead of a 440 VAC.