Hi everyone - would greatly appreciate any insight y'all might have on this A/C mystery. Getting awfully hot upstairs around here!

Symptoms are as follows: blower was coming on, but blowing room temp air; house was obviously not cooling. Inspected the condenser unit outside, and the fan was not turning, and the coolant lines into the house were not cold at all as they should be. This is a Carrier unit, about 6 years old. When the thermostat inside the house tells the unit to come on, there's a click and then a bunch of humming, but nothing else. This started sort of suddenly yesterday afternoon when we noticed the temperature rising.

Here's what I've tested so far: Powered the unit off, and took the grill and fan off the top - fan appears to spin freely although I suppose that could still be the problem. Put the fan and grill back on, and opened the electrical panel on the outside of the unit. With the power on, the voltage heading into the contactor (I think it's called?) read 240V so I'm getting good power to the contactor. When my "helper" (read: frustrated wife) turns the digital thermostat on upstairs, there's a 'click' (but contactor stays in the 'out' position). After a minute or two, the thermostat appears to send the signal to turn the unit on, because I could visibly see the contactor pop "in" and then the humming started (but no fan movement or anything else). The humming sound seemed to be coming from inside the condenser area and not from the contactor itself, but hard to tell. Voltage across the control lines read 27V but that was probably not the deal anyway since the thermostat was clearly able to talk to the condenser. Have jiggled and confirmed good contact with all leads and connections I could reach.

I did *not* test the voltage on the other side of the contactor - is that worth doing? I assumed that 240V coming in plus a visibly working contactor probably meant it was not the contactor. Knowing nothing about contactors other than they're apparently some kind of magnetic switch, is there a fuse of some kind inside the contact that could be blown?

Any recommendations? How would I go about testing the capacitor? Or should I just try to replace it since it's supposedly cheap? Sheepishly, I have not cleaned the condenser coil since we bought the house new 6 years ago - could that be the problem (or part of the problem)? Seems like it would not since that should not impede the fan from turning. Have attached a picture of the electrical setup.

Thanks very much. Crossing my fingers that the issue is simple and cheap!

 

Looks like the top of the cap is swollen to me....rusty for sure but it also looks like the terminals are sorta "splayed" out. Your symptoms describe a bad cap almost to a T.

 

Thank you very much - off to HVAC Supply to pick one up - will post back with what happens!! Thanks again for the reply! Looks like a fairly standard 370V 35uf/5uf one so hopefully not too hard to find...

 

Hey, thanks for the great advice. $18.96 at Grainger and an extra machine screw or two at Home Depot later, the thing is working perfectly. Cooling the house down now as we speak.

Thanks again - worked like a charm!

 

Glad it was that simple. Nice price too!

 

For sure! I was dismayed at the potential hundreds of dollars it could have costed. Really appreciate your comments, and previous posts in this forum that gave me the courage to take a crack at this. Thanks again!

 

hi, I am having the same exact issue as the OP, went down and got a replacement capacitor 35/5 440VAC and put it in one wire at a time. turned on the breaker and nothing, then a few min later i hear it click.

any idea? did i get a bad brand new capacitor?

 

That post is 2 years old. Do you have a Carrier unit?
Is the compressor running without the condenser fan motor as the thread is titled?

 

I'm experiencing this issue as well. I've got a Carrier 38TUA-024 unit. Voltage into & out of the contactor is 240V. I get compressor buzz, but fan doesn't spin. When I turn it on, I get a quick buzzing sound that lasts ~1 second, but nothing more. My capacitor is not bulging like the one in the picture. Fan motor is hot to the touch, like it's trying to work. Fan spins freely in both directions when spun manually.

So, my question is whether I should try replacing the capacitor first (since it's cheap), or should just try to replace the fan motor right away. Any thoughts?

 

I recommend that you replace the cap.





It is easy to check a cap. Turn off power, wait 3 minutes, verify that the cap has bled down by shorting the terminals to ground with a screwdriver, write down the terminal = color combination, remove the wires and measure C to Herm and C to Fan on a dual cap or measure across the 2 posts of a standard run cap with a meter that measures capacitance.

 

I had the same issue as Encino50

blower was coming on, but blowing room temp air; house was obviously not cooling. Inspected the condenser unit outside, and the fan was not turning, and the coolant lines into the house were not cold at all as they should be. This is a Carrier unit, about 6 years old. When the thermostat inside the house tells the unit to come on, there's a click and then a bunch of humming, but nothing else. This started sort of suddenly yesterday afternoon when we noticed the temperature rising.

I went down to the local Ferguson's HVAC center and they matched the capacitor to a generic one for $10. Went home and changed it out. BAM! House blows cold once again. This thread saved me at least $160 (I thought it was the fan motor) and triple that if I had called a technician.

 

Welcome to the forums.

Glad that this thread helped you out. I can see it's a hot topic.

Unfortunately it is getting too large to keep in general circulation. It will be sent back to our searchable archives where it will always be available for reference.

If you have a question or problem that was not addressed here.... please feel free to start a new thread. You can link to this thread in your new thread.