Problem with compressor...please help

[Greyhound]

Hi all...new to the forum here. Through the summer, I've had trouble with my Fridgiare a/c compressor off and on. It began by occasionally throwing the 40a breaker. I removed the shroud and the coils were completely dirty. I thoroughly cleaned them, put everything back together and I had no trouble until a few weeks later when the breaker tripped again. This time, I changed the run/start capacitor since the capacitance measured a bit low (supposed to be 40...measured 28). No problems after that...until about a month later. I woke one morning to a frozen line. I killed power to the compressor and called a service tech who came out and said I was 1lb low of freon. He charged it up and it has been fine...until today. I got home this evening and noticed only the fan running. The compressor would try to kick in but after a second it would kick back out. When I flip the breaker to the unit I can hear a hum...it only hums when the fan inside the house is running (thermostat in cool mode). Can someone tell me what my problem may be or where to start looking? I thought if the compressor was locked it would trip the breaker from too much in-rush current or am I wrong? Please help.

Additional info: it's not a heat pump...not sure whether that makes any difference or not but thought I'd add it anyway.

[HayZee518]

any motor draws 125% more than nameplate current when it starts. did your a/c tech add any oil to the system? oil lubricates and cools the compressor drive motor. if you can find someone with a clamp around amprobe, measure what you have for current on the compressor leads. once you find this out we'll take it from there.

[Greyhound]

The service tech didn't add any oil. I have an amp clamp. I'll measure the current and report back.

[Greyhound]

Got up this morning and removed the capacitor and measured its capacitance. Since it's a dual cap, it should measure 7.5 and 40. It measured 7.5 and 494. How is that possible and would that cause the problem I'm seeing?

[HayZee518]

how did you measure the capacitance of the cap? if you used an ohm meter, especially a digital meter, you CAN'T measure capacitance with a digital meter! An analog meter will tell you if the capacitor is good or bad. With the resistance on its lowest range R X 1 you put the probes on the common and one side. the needle goes upscale then back down scale. reverse the leads and apply again. the reading will go upscale and then downscale. If the analog meter does this, the capacitor is good. A capacitance meter is needed to actually measure the capacitance - those meters are not cheap either!

[Greyhound]

I measured it with my Fluke 179 digital multimeter. Back during the summer, I replaced the capacitor and before I replaced it, I measured it to see what exact values I would get. It measured 7.5 and 40. Now, it measures 7.5 and 494. My Fluke (even though it has a capacitance setting) is not capable of measuring capacitance?

[HayZee518]

digital meters do not measure capacitance. analog meters don't either. meters use an internal battery to impress a voltage across the probes when testing resistance. the capacitor will only charge up to the applied voltage the meter can supply. if the cap is rated at 370 volts, it'll only get to 3 or nine volts of the meter's battery. go out and buy a new dual section capacitor and replace it for what you have. you won't be pulling hair out of your head trying to determine if the cap is good or bad.