Air Conditioning - Outside unit hums but does not work

The inside blower works fine.

The outside unit the fan and compressor don't seem to come on. Instead I just hear an audible hum (sounds very similar to me as the electrical hum you get when you grab the blades of a box fan and the motor struggles unable to turn against the extra load).

I figured the fan had sized up. However, when I turn the system off and push the blades of the fan they turn freely (didn't try and push the blades with it on).

:wall:

Try and spin the blades in the correct direction, using a stick, when it calls for A/C. If it spins and runs, then you probably need a new capacitor. Since you say neither comp or fan run, you may have a cap that handles both. $10-15 at most HVAC stores.

Do not leave it running as this only tests the fan/cap...the comp can be damaged if you keep trying to start it w/a bad cap.

Very common problem at the beginning of the cooling season.

pushing the fan with everything on doesn't kick start it. Still has the hum.

What else can I check?

Is the hum definitely coming from that fan and not from a contactor solenoid, let's say? Have you checked for voltage leading to the fan and compressor?The fact you do get this hum, leads me to believe you at least have the 24 volts out there, but either the contactor is not letting through all the juice, or the capacitor isn't, or the fan motor went out and also the compressor went out(seems unlikely though, especially if the whole unit has been allowed to remain off for some time to cool everything down, in case anything triopped otu on high-temp overload).

Since the capacitor is as cheap as they are, you could try a new one, as Gunguy suggested. Not out much money to eliminate that from the equation.

If you are a novice, working with electricity, do not work outside your comfort zone. Either get a pro, or ask people here some very specific questions. You are dealing a killer 240 volts out there! Even certain capacitors can store a charge even after the power is shut off, and you need to test and see if a charge still remains and short if necessary to drain, before handling.

I don't have a volt meter on hand, but I might go pick one up if you think that is needed.

I'm positive the "hum" is coming from the fan motor and not the compressor.

Here the model number info if that helps at all:

http://img122.imageshack.us/img122/9674/1002009.th.jpg (http://img122.imageshack.us/my.php?image=1002009.jpg)

Here is the unit with the panel removed:
http://img122.imageshack.us/img122/7816/1002005.th.jpg (http://img122.imageshack.us/my.php?image=1002005.jpg)

I'm pretty sure the top cylinder is the solenoid, and the bottom is the capacitor. I'm a bit concerned with the "crud" that appears to have leaked out of the capacitor?

http://img122.imageshack.us/img122/1407/1002006.th.jpg (http://img122.imageshack.us/img122/1407/1002006.jpg)

I'll post again once I get a volt meter and can check that all the wires are hot, but as nothing seems disconnected and there is that hum I'm thinking the power is there. But you never know.

Edit: switched the images to clickable thumbnails to be less obnoxious.

I'm not sure what the bottom can is...I see a resistor on it....??

The top can is the capacitor. Black item with brass visible to the right of pic 3 is the contactor.

The bottom "can" is a start capacitor, actually that along with the relay next to it is a factory installed hard start kit.

After seeing that filthy coil I would look to see if you have a high pressure lock out. Look for a little red botton along the bottom of the unit or a little knob with two wires coming out of it attached to the copper pipes inside the unit.

I think what you are hearing is the contactor coil.

Do you have 240 volts to the contactor and after the contactor?

You said "crud" leaked out of the CAP. .If the cap. is leaking or looks swolen it is bad. Voltage problems,lightening or age could cause it to go bad. Replace both capasitors.Make sure POWER is OFF and short cap leads to ground before touching them.

Kilowatt,

No, I don't see anything like that. What is a pressure lock out?

Others,

About the voltage. I have the volts between the postive and negative leads from the house to the contactor

but sticking the probs on the volt meter between the negative lead (from the house) and every other point on the contactor and both the capacitors and anything else I could think of to touch with the probe showed 0 volts.

I then repeated the steps but by moving both negative and postive probes, again the only thing that appeared hot was when i had the probes on the leads from the house.

So, does this mean both my capacitors are out? where do I go to replace them? Home depot didn't seem to have them.

Thanks for everyones help so far.

Also, the companies I called want 80$ per half hour (160$/hr). That seems like a lot. I don't think a surgeon charges that much for his time. Is that about right? well hopefully I can just replace these capacitors and be done with it.

Sometimes you have to spend money, it's cheaper than a funeral.

HotIn...just to clarify..there is no positive and negative when you are talking about AC voltages (residential). It's common to hear "hot", "neutral" (I've also heard "return") and ground.

Replace both the caps, (go to an HVAC supplier), see if it works, otherwise I think you may be loooking at a service call.

That is a Trane or American Standard unit. it doesn't have a high pressure switch. I can't tell from the readings you took whether or not you have power at the outdoor unit. Follow thw ires that come from the disconnect swtich to the unit. Test across those to see if you have 240 volts. The crud from the start capacitor is indicative of other problems. Frankly. you're in over your head. $160 an hour? Are you in the Houston area? That's enough to tempt a guy to come out of retirement. Let us know about the volts test. Thanks.