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Old 08-06-2011, 08:20 PM   #1
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Breaker pops on Lennox HS24-651-1P


I read what Yuri posted in the past about hard and soft shorts. My 50 A CB pops immediately but only opens slightly. My understanding of what he posted is that this usually does not incicate a dead short, as someone else thought I most likely had a shorted compressor.

I have isloated all wires in the control box from their terminals (by detaching them). Ohming each against ground I found no resistance (no circuit).

I also ohmed the wires going to the fan and the set going to the compressor. No resistance was measured probing any wire and ground. Wire to wire I got the following readings.

Compressor
B to Y: 1.9 Ohms
B to larger R: 1.6 Ohms
Y to same R: 3.1 Ohms

Fan
Or to Purp: 52 Ohms
Or to B: 23.4 Ohms
Purp to B: 28.5 Ohms

Crancase Heater
Measured open across to terminals disconnected from Line side of L1 and L2. No resistance terminal to terminal. Disconnecting the heater and attempting to run the old girl made no difference.

Many of the disconnects were loose. The two from the load side of both lines to the compressor (not sure of gauge but looks like 10 or heavier, one red and the other black) were really bad. The one on L2 was partially welded to the contactor terminal.

I have a really basic digital meter that does not test capacitors. There is a start capacitor and a dual capacitor. Neither look bad, except the dual capacitor is covered with rust. Ohming all terminals to ground I got an open circuit. Nor was any resistance measured terminal to terminal.

The fan runs with the three wires to the compressor disconnected, but the CB pops if I try to run the AC with the fan disconnected and the comprssor connected.

Coolant pressure is probably very low, but I doubt that would trip the CB.

Any suggestions will be greatly appreciated.

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Last edited by Klawman; 08-06-2011 at 08:30 PM.
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Old 08-06-2011, 08:33 PM   #2
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Breaker pops on Lennox HS24-651-1P


Check for a short to ground in the compressor.

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Old 08-06-2011, 08:42 PM   #3
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Breaker pops on Lennox HS24-651-1P


From what he described he checked for a short on the compressor, or so it seems.
The other possibility is that you have a bad breaker.
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Old 08-06-2011, 10:09 PM   #4
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Breaker pops on Lennox HS24-651-1P


I just got back from buying a new digital multimeter that I believe will check capacitance, but yes I spent quite a bit of time checking for a short in the compressor. I think my old digital would have measured a short. Had there been one, wouldn't I have read some nominal resistance with one probe on the disconnected wire and the other toching ground. I got nada and am pretty certain I was properly using the meter (kind that you may get nothing on a high setting like 2000K ohms but will measure a tad on 200 ohms (resistance between the probes when touched). Anyway, I will retest with my newer meter, which is supposed to check capacitance.

As for it being a bad breaker, I wondered about that. Is there a way to test it? Measure voltage across the lugs? I don't have another 50 but I have a 40 amp I could swap and see if it pops.

Yes, I know the importance of being careful with the board opened. (I have been planning on running a sub panel to the garage and adding 240 to it.)

Last edited by Klawman; 08-06-2011 at 10:14 PM.
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Old 08-06-2011, 10:18 PM   #5
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Breaker pops on Lennox HS24-651-1P


take the 3 wires off the compressor terminals after labelling them or drawing a map. Then check for continuity from each terminal to the copper larger/suction line of the compressor. If you use the black shell the paint is an insulator and if you scrape it the results are not accurate. Techs use the copper line to be sure.
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Old 08-07-2011, 12:42 AM   #6
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Breaker pops on Lennox HS24-651-1P


Quote:
Originally Posted by yuri View Post
take the 3 wires off the compressor terminals after labelling them or drawing a map. Then check for continuity from each terminal to the copper larger/suction line of the compressor. If you use the black shell the paint is an insulator and if you scrape it the results are not accurate. Techs use the copper line to be sure.


Done. No resistance or continuity measured and this time I had a slighly less crappy meter; a Commercial Electric knock off of a Greenlee and it did prove to be more accurate than the little GE digital that cost half as much.
This time I didn't measure the ends of the wires at the control box, but I measured at the actual compressor after removing the fan assemble and partially opening the instulation blanket (fortunately it was velcro). I also looked at the heater and noticed nothing to indicate a problem. As the leads were sealed from what I could see, I relied on readings taken of the wire disconnects inside the control box.

I was told that I should have read resistance across those wires as each run from one end of the crankcase heater to the line side of the two contacts. Before I couldn't get a reading with my old digital meter; not ohming the disconnects to ground or to each other.

This time I got to readings across the crankcase heater terminals (disconneted from the contactor). With the meter set on "auto" (I believe that was the setting) it read "1.307KΩ”. While cycling through meter “functions” I got a reading that I think was for a a diode of .585 V.

I am beginning to wonder if the problem is the circuit breaker.

BTW, can anyone tell me if this little Commercial Electric digital multimeter can be used to check capacitors. On the back it says it has a “capacitance” function. I can’t find any instructions on how to use it online and none came with it.

When the dial is rotated to a setting first switched to the setting marked with "CAP", a diode symbol, and and an Ω it gives a reading for "nF", which I beleive means nanofarads. If I am correct how do I use the meter to check the comprssors start and dual run capacitor?

Last edited by Klawman; 08-07-2011 at 05:08 AM.
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Old 08-07-2011, 05:36 AM   #7
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Breaker pops on Lennox HS24-651-1P


Should have a setting marked, MFD, or uF.
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Old 08-07-2011, 05:39 AM   #8
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Breaker pops on Lennox HS24-651-1P


Take another ohm reading across the compressor terminals again, using your new meter, and post them.
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Old 08-07-2011, 05:42 AM   #9
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Breaker pops on Lennox HS24-651-1P


Quote:
Originally Posted by beenthere View Post
Should have a setting marked, MFD, or uF.
I hear you. Until I can mess with it in the morning I am not going to know for sure. If it detects a greater number it may automatically switch to a MFD scale, but I believe there are a thousand nano farads to a single MFD and it is possible what they sold me will only measure small capacitors.
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Old 08-07-2011, 05:47 AM   #10
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Breaker pops on Lennox HS24-651-1P


Quote:
Originally Posted by beenthere View Post
Take another ohm reading across the compressor terminals again, using your new meter, and post them.

Will do. I only measured to see if each winding is shorted to ground and found none. This one also has an audible for a closed circuit and it didn't go off. This was measuring of the condenser to the copper suction pipe. I think that is what it is called.

I think what you want me to do is measure wire to wire again. Yellow to Black, Yellow to Red, and Red to Black.

If this thing won't measure the capacitance of this size, I think they have a Klein for another $25.
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Old 08-07-2011, 06:00 AM   #11
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Breaker pops on Lennox HS24-651-1P


Put your probe directly on the compressor terminals, and measure the resistance from each terminal to the other.

Common to start, common to run, and start to run.
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Old 08-07-2011, 06:02 AM   #12
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Breaker pops on Lennox HS24-651-1P


Quote:
Originally Posted by beenthere View Post
Put your probe directly on the compressor terminals, and measure the resistance from each terminal to the other.

Common to start, common to run, and start to run.
Got it and will do. Thanks.
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Old 08-07-2011, 02:19 PM   #13
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Breaker pops on Lennox HS24-651-1P


Quote:
Originally Posted by beenthere View Post
Take another ohm reading across the compressor terminals again, using your new meter, and post them.
Done and done. These readings were done at the compressor termianal and they were the same as taken of the disconnected wires in the control box (as adjusted for the fact that 0.6 Ω is zero on it, what it reads when the probes are crossed).

The actual readings taken with the new meter are:

Y to B: 1.4 Ω
Y to R: 1.2 Ω
B to R: 2.4 Ω (I may have posted this as Black to Purple the other day. My bad.)

I also tested the capacitors. The dual capacitor read 10.41F between Common to Fan, but only 1.91 nF between Common and Hermes. With the three wires to the compressor disconnected at the control box, the fan runs.

The comp start capacitor read 0.19 nF.

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Old 08-07-2011, 05:12 PM   #14
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Breaker pops on Lennox HS24-651-1P


The ohm readings of the compressor are slightly off, could be due to the meter.

Your cap reading for the fan, is high, an d the others are low. may just need new capacitors.
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Old 08-07-2011, 05:26 PM   #15
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Breaker pops on Lennox HS24-651-1P


Quote:
Originally Posted by beenthere View Post
The ohm readings of the compressor are slightly off, could be due to the meter.

Your cap reading for the fan, is high, an d the others are low. may just need new capacitors.
This thing is 20+ years old. I am only guessing but that might account for the ohm readings being off. Anyway, I think I am at the point where I may as well try some new capacitors. Can you tell me the part numbers for the dual run capacitor and the start capacitor. I am going to take them off the side of the control box to get a better look at them, but the dual is so rusted I may not be able to read the number or the ratings.

I have located a dual capacitor for a Lennox that looks like it (an oval dual capacitor), but I don't know if it is rated for my model. It has a pa Manufacturer Part No: 53H2201 and is described as "53H22 -- 53H2201PR DUAL RUN CAPACITOR 25+5 MFD 370 VAC"

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