HVAC Not Running

[mcp6453]

Our downstairs area has a Carrier heat pump system. As of yesterday, when the thermostat calls for cooling, the outside unit (fan and compressor) just buzzes. The fan does not spin, and the fan motor gets really hot. If I spin the blade with my hand, it starts running but not at full speed.

It seems to me that the starting capacitor has failed. I took the cover off to see what I could see, and the capacitor is clearly bubbled on the top. Hopefully I can find one on a Sunday to replace it.

Even with the fan running, the air is not cool. Here is the magic question. Could the fan running at lower-than-normal speed cause the unit not to cool?

This problem occurred after a thunderstorm. There were some extremely close strikes, but as far as I know, nothing else got hit, which leads me to believe that the failure was coincidental. Even if lightning got the capacitor, it's no big deal. Hopefully the compressor and controller board are still working. (I don't know how to tell if the compressor is running.)

[Ed Pawlowski]

+

Yes, the job of the fan it to carry the heat away. Compressor running? Is the coil getting hot? Is the evaporator coil freezing up?

You can usually hear the compressor running. It should be starting (at least on older units) even if the fan does not run Or the lightning fried the controls.

[Stormin Mormon]

Usually compressors make a distinctive noise. You can also check the amp draw. But for now, I'd suggest to replace the capacitor. Fairly inexpensive item and a common culprit. Finding one on Sunday? Only if some HVAC company near you is willing to sell you one. Might need to wait till Monday.

. Christ> Our downstairs area has a Carrier heat pump system. As of yesterday, when the

[trader4]

Sure. The fan has to carry the heat away. With poor air flow, it's not going to do much cooling.

You should be able to tell the sound of the compressor motor from the hum of the contactor/relay. Also, normally the pressure line is warm, the suction line cold, at the unit. With it underperforming, the difference will be less, but I would still think you'd feel some difference. From the description, sure sounds like it's a bad cap.

[mcp6453]

The capacitor is a GE 97F9969. It's a 7.5/45 at 370V. Both sections are open, so it's definitely bad.

Here's my next question. A friend who just had a similar failure bought a spare capacitor for his heat pump. However, it's a 5/45 instead of a 7.5/45. If I install it, and if the fan starts, is there a problem using the wrong part until I can get the correct one tomorrow? Since capacitors change value over time anyway, I suspect it will be fine for short-term use.

My primary objective is to find out whether the cap is the only problem. If lighting caused this problem, I need to determine whether anything else is damaged so I can get a service call in.

[trader4]

I don't know what kind of test you performed, but a cap normally appears open to DC.

I would think it would be fine for temporary use too.

I would stronbly suspect that the failure is unrelated to the lightning. The typical lightning mechanism is a surge coming in on the AC. If that happened, there is a good chance you would have seen other problems in the house. Or that the electronics in the heat pump system would have been fried, etc. The fact that the only symptom is that the fan isn't running and the cap is bulging would suggest to me that it's just normal cap failure.

[mcp6453]

I put the new cap in, and it appears to be working. The fan started, and I'm waiting to see if it's cooling. The compressor does sound like it's running.

You can test a cap by shorting its terminals and then checking it with an ohm meter. You will see an instantaneous short circuit, but then it charges to open circuit.

Thanks for the input.

[The Daring Dufas]

That's a double capacitor for both the fan and compressor. The 5mfd is for the fan and the 45mfd section is for the compressor. Lightning blows those things out all the time. The 5/45 may work OK until you can get the proper replacement but get a 440volt rated capacitor instead. The higher voltage rating will hold up longer than the lower voltage 370volt cap. There is a real problem in the HVAC industry with Chinese manufactured capacitors that don't hold up and don't meet voltage/mfd ratings and have a high failure rate. There are websites that sell American made capacitors that have become popular albeit much more expensive. ^_^

TDD

[Stormin Mormon]

Should work, fine.

. Christ>

[Stormin Mormon]

With a swing meter VOM, that's a crude check. You're welcome.

. Christ>

[micky]

If you are using a digital meter, this works even better with an analog meter. Easier to see what is happening. When it's not a little cap that fills before you know it. AC caps are not little.

[jamesgang]

As you figured out that size is fine. For what it's worth, that is not a start capacitor, it's a run capacitor.

[mcp6453]

The replacement capacitor is 45/7.5/440V. Accordingly, it's larger. It does not come with a mounting bracket like the old one has. The electrical supplies house didn'0t have one. I secured it with a 3" cable clamp and ran a screw through the leftover tab after tightening the clamp. It seems to work great.

Anyone know where I can get a clamp? TRADEpRO TP-CAP-45/7.5/4440R MFD

[Tony Hwang]

Hi, Replacing with bigger cap value is OK not the other way around. If it is well secured why bother?

[Stormin Mormon]

Just use some perforated strap.

. Christ> The replacement capacitor is 45/7.5/440V. Accordingly, it's larger. It does not

[trader4]

It's not a bigger cap. It's one that has a higher working voltage rating. That is OK to substitute. Replacing it with a cap that has a larger capacitance would not be OK.

[mcp6453]

That's essentially what the clamp did, but I thought about using perforated strap. Who sells it? Lowes?

[Stormin Mormon]

Lowes or HD, or auto parts places. With a hose clamp that works, I'd quit here and not go through the effort.

. Christ> >> Just use some perforated strap.

[The Daring Dufas]

You'll probably find the perforated metal strapping in the plumbing department or the isle where all the metal sheet, bar stock and punched angle. ^_^

TDD

[micky]

I just bought a roll of that last year. Cheap it was. I think it was at a bicycle store. Or if not that, Ace Hardware. Or if not that, HD.

But you don't need a clamp, just a leash. To keep it from going too far.

Or try saying to it "Stay!".

Many of them are partially trained at the factory.