So, noticed this evening that the AC was only blowing lukewarm air. Went outside and noticed the outside unit's fan (where the compressor is) wasn't turning and I didn't hear the compressor.

I checked all the breakers but no issues... turned things off at the thermostat then back on again, went outside and heard the compressor start up. I manually pushed the fan blades with a long screwdriver and the blades started spinning and I got cold air out of the vents.

After 5-10 minutes or so the compressor shuts off and so does the fan (though the fan on the furnace keeps going).

Initially I thought this was the start capacitor, but since things shut off after running for a while I'm not so sure...

 

That fan does not have a start capacitor. A start capacitor is only in the circuit on startup.

That fan uses a run capacitor which is in the circuit the entire time that the fan runs.

The compressor uses a run capacitor. The compressor often also has a start capacitor.

Carrier often uses a dual run cap that serves the compressor and the fan.

 

Thanks.

So sounds like it could be this dual-run capacitor... I was thinking the fact that it ran for a while (with a manual fan start) could point to low coolant or something else triggering an over-temp protection mechanism on the compressor.

HVAC company is booked this week so looks like I'll be tinkering a bit in addition to calling around!

Will try and get the make/model of the Carrier unit a bit later.

 

I have the same problem here. Could it be the capacitor in the condenser? It was running fine this morning and when I got home an hour ago, no more cold air. The fan is no longer running. I still hear something out of the condenser.

 

Are you able to tell the thermostat to ask for cooling, audibly hear the compressor kick on and then manually start the fan?

This works for me -- for about ten minutes, then it all shuts off and I have to redo the process to get cool air going again.

Got someone coming Wednesday so probably won't tinker too much further myself.

 

Variant, I hear the compressor but no fan. I believe I have this problem before and it was the run capacitor.

It is either the run capacitor or the fan motor. I have not change the run capacitor for 3 years. It is an old system (1991).

 

Usually if the fan runs for a while.... like an hour.... and then stops..... the motor is shot.
As the bearings heat up the motor starts to bind.

 

Does this mean the motor is PERMANENTLY dead?

 

No.... it's fine when it's cold. It's not permanently dead but it's not very useful if it binds up and stops running.

It's permanently dead when it does nothing.

 

For my issue I'm pretty sure it must be the run capacitor. Doesn't look like Home Depot carries the right kind, however (or the guy who answered my call was clueless).

This seems to be what I'm after:

https://www.amazon.com/Carrier-P291-.../dp/B00S02ZQ6I

I opened up my outside unit and there doesn't *appear* to be any obvious damage to the existing capacitor, but I'm guessing the symptoms kind of line up with the compressor only running for 10 minutes or so and then shutting off (and fan needing to be manually started).

 

PJMax, beside the dual run capacitor and fan motor being possible defects, what else could prevent a fan from running?

Variant, I believe grainger also carries dual run capacitor. If there is one close to your house, you can go there. I am stopping by tomorrow morning. Usually, I but mine from Amazon or HD. Replacement of a run capacitor is actually common.

 

Guys, go buy a meter that can check a capacitor so you know whether the cap is bad or not.

Although I already own a Fieldpiece Clamp meter that can do pretty much everything, I bought a Uni-T, on Houston's recommendation, to keep in my car. The thing is a true-rms mini clamp meter and it can check capacitors.

The only thing I wish it did was check more than 100 amps and could check inrush current. But my Fieldpiece does that. For under $40 shipped to the house, I don't think you can beat the UNI-T UT210E... https://www.amazon.com/Uni-T-UT210E-...=1&*entries*=0

 

Hi Crabjoe,

I agree with you but the problem is, I don't know how to use one of those to test the capacitor.

BTW... would this be similar to the same thing?
7 Function Clamp-On Digital Multimeter

 

Just make sure it can handle/measure capacitance and the proper range of microfarads. The description in your link makes me think that one can't? I think it should have a symbol on it like this -||- or -|(-

https://www.amazon.com/Tekpower-MS82.../dp/B013HD5Z5G

There's one that appears it could do the trick.

 

(Or use the one joe linked to -- looks nice!)

Looks like there's a Grainger in my area, but it's just far enough away that it'd be a pain to get to in SoCal traffic. I may give them a call and see if they do any sort of delivery, but with the HVAC guy coming tomorrow I'll probably just hold off.

The other thought I had was trying to find a 7.5uf/370v capacitor and wire it up alongside my dual capacitor to run the fan (which is 80+7.5uf/370V). This assumes the capacitor for the compressor is fine and that it's only because the fan isn't running full tilt that the compressor kicks off due to the fan not being able to remove enough heat. I've seen people run water over their coils too???

...If I can find one where Amazon will do same-day delivery (unlikely!)

 

Found a local electronics shop who carries the capacitor so am going to snag it this afternoon and swap it out this evening.

 

So, swapped out the dual cap this evening with a slightly larger one (80uf/10uf/440v). Seems to have done the trick!

Thanks for all of the insight... have learned a lot about my HVAC and saved a bunch of money too.

 

Testing is pretty straight forward.. attach the leads to the meter, set it to check capacitance, connect the black lead/test probe to the C on the capacitor, connect the red probe to the FAN and see what it reads... If it matches what the capacitor is rated for, you're good. If it doesn't, you need a new cap.

If you need to, there's tons of videos online on how to check a capacitor with a meter.

BTW, if you do do this, make sure you've discharged the cap before messing with it and the wires are removed.