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Lennox AC HS24-651-1P


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#1 klawleman

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Posted 04 August 2011 - 01:36 PM

This is the AC compressor that came with the house and it is over 20 years old.

As soon as the A/C is switched on, you hear a click (I think it is coming from what you call a contactor) on the outside compressor click and the breaker pops. If I stand and watch, I see a spark at one of the contact points as it closes (the one on the side with the thicker red wire that I assume is line in) The blower located in the attic continues to blow hot air.

I have the access cover off and while the dual capacitor is covered with rust I see no bulging or any leakage. The comp start capacitor looks fine.

A wire looks pretty fried, BUT THIS MAY HAVE BEEN LEFT LIKE THAT BY A SERVICE REPAIRMAN 15 years ago. It was the second time he came out. Both times a "bridge" in the relay had fried, he said something about the poor design and changed the part the second time from a two to a three bridge contactor (I believe), which was about two years after the relay fried the first time.

I have a digital multi meter and have removed the disconnect block. Can you suggest what I should check? My guess is that the damaged wire isn't the problem. The damage is no where near where it could be causing a short. TIA.

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#2 ACtechGUY

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Posted 04 August 2011 - 04:03 PM

You have a dead short to ground.. Here is how to isolate the problem
LABEL and disconnect the 2 wires from the contactor that go to the compressor . Also disconnect the last wire from the compressor that is attached to the capacitor. Make sure they are not touching any metal for the test.

Now take an OHM reading from each wire to ground( Ground is any clean peice of metal attached to the chasis like a screw) . You should have a very high resistance ( IN THE MILLION OF ohmS) . If you have thousands or lower resistance , the compressor is internally shorted to ground (FAILED, DEAD , DECEASED, GONE PECAN, KAPUT........)

But There is still hope!!! It could be a simple burnt wire in the compresser teminal box. So take the cover off where the wires go into the compressor and check for burn wires.

If no resistance to ground is found check OHMS wire to wire .

If compressor looks ok , do the same test for the fan motor . it is possible but not likely to be shorted to ground internally.


We will go from there when you report back what you have found.

Edited by ACtechGUY, 04 August 2011 - 04:06 PM.


#3 klawleman

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Posted 04 August 2011 - 04:33 PM

I will do exactly as you suggest (the labeling the wires and connections is a great tip). Meanwhile, I attempted to test the "capacitor comp start". I guess that means the compressor start capacitor and this is what I found.

I isolated the start capacitor from the rest of the system. Its terminals were heavily corroded making it difficult to pull the wires. Ther is a resistor soldered across tbose terminals that was pretty ugly and possibly burnt.

Reading the terminals either polarity on 200K ohms I get an intial readin of around 6 that climbs over about a half a minute ot 14.59 (it keeps slowly climbing and I don't know how much higher it will go). Set on 200 ohms I get a momentary reading of as much as 198 before the meter drops to Zero. I think that means the measurement is off the 200 ohm scale and it has 1,459 ohms resistance. Do these readings tell you anything? I wonder if I am simply measuring the resistor soldered across the terminals.

Now I will get on as per your instructions and search for a short, but I will check back to see if this tells you something, other than I don't know what I am doing. Thanks.

#4 klawleman

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Posted 04 August 2011 - 06:24 PM

This took me a while. I wanted to make sure I was measuring the correct wires.

Measuring from the wires disconnected inside the control box, I measure no resistance on any.

While trying to figure out what wire went to what, I found that the the thin (approx 16 AWG) black wire coming from the house was installed so that its insulation was pressing against the non insulated contact for the same size red wire on the appeared to to energize the L1 contact coil. The insulation of the black wire was in terrible condition and if it was a ground I would think it could have caused a short. Still, it didn't look like a short as nothing looked burnt.

I am going to disconnect and check all the other wires in the contol box to see if they short out.

#5 ACtechGUY

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Posted 04 August 2011 - 07:16 PM

A failed start or run capacitor will NEVER cause a circuit breaker to pop instantly.

I wonder if I am simply measuring the resistor soldered across the terminals.

yes and no. From what you describe , the start cap sounds ok .



put all wires back where they belong and check at both "load " and "line" of the contactor for ohms to ground. if you get no resistance to ground , then try to restart the unit.

A possibility is a problem in the circuit breaker box itself or in the conduit between the ac unit and breaker.

But the fact that the contactor sparks indicates a shorted to ground or faoled compressor.

#6 klawleman

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Posted 04 August 2011 - 07:38 PM

I is stumped. Let me run some stuff by you to see if it sounds like I metered the thing correctly.

I am using this inexpensive digital meter with a highest ohm setting of 2000K and a lowes to 200 Ohms. When the test probes are touched on 200 ohms I get a reading of about .6. I don't read anything when I probe the disconnected wire going from the contactor to the compressor with the other probe on ground. Even if there is a short in the compressor motor, shouldn't I get a reading or am I not getting one because the highest setting on my meter is 2000K ohms?

Disconnecting all wires form their terminals in the control box none read anything when ohmed, except the two (a yellow and a black) leading into the house. I didn't record what was read but it was something like 26 ohms for black and 14 for yellow.

This is true of the three wires going to the fan motor.

#7 ACtechGUY

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Posted 04 August 2011 - 10:32 PM

When the test probes are touched on 200 ohms I get a reading of about .6.

You are reading the resitance of the meter leads === .6 ohms

If you were going to get a reading you would get it to ground on the lowest range of your meter (200 ohm)

DID you test all three compressor wires to ground? What is the wire to wire ohm reading ?
Say we have a black a brown and a yellow wire to the compressor. black to yellow might be 14ohms black to brown might be 10 and yellow to brown might be 4 ohms. those readings are examples , but use it as a loose guide to check the windings. You should never have a reading to ground on any of those wires.
As a mater of fact you should have NO readings to ground on ANYthing in the condenser.


Assuming you compleatly disconnected ( isolated ) the 2 main power wires feeding entering the condenser, and you have a resistance to ground when you read those wires going back into the house , then you have a short to ground in the wiring coming from the inside panel to the unit. Maybe if there is a service disconnect nearby the unit the problem is in there.

This is true of the three wires going to the fan motor.

What is true? that you have resistance to ground or you get nothing? Me no too sure which.....

************************DISCLAIMER****************
I have never owned a manual adjusted Volt meter . I have ONLy used FLUKE autoranging meters. So I may be wrong as to what scale you need to set your meter to.

#8 klawleman

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Posted 05 August 2011 - 05:18 PM

DID you test all three compressor wires to ground?


Yes and none measured resistance I take to mean those are not shorted.

What is the wire to wire ohm reading ?


There are actually 5 wires going to the compressor; a black, a yellow, and three red. One red is the same gauge as the black and the other two red are smaller. I believe it says 600V 10 SC on the small stuff.

Wire to wire:
B to Y: 1.9 Ohms
B to larger R: 1.6 Ohms
Y to same R: 3.1 Ohms

The two smaller reds come off the line side of L1 and L2, which have the heaviest gauge coming from the nearby disconnect box. With the CB off and those two disconnected, but the disconnect closed, I ohmed them to each other and each to ground. No resistance measured.

Also with the CB off and the main lines disconnected from the line side of Line 1 and Line 2, I no resistance was measured to ground or each other.

Singnal wires from house:
What I had called a B wire is actually pig tailed to a very light gauge white wire. That B wire goes to the coil terminal of the contactor's line 1 side. It measured 26 Ohms resistance to ground.

The Y wire actually pig tails to a light gauge R from the house and that Y goes to the contactors L2 coil. Measuring from its isolated terminal to ground I get 1.4 ohms.

FAN MOTOR:

There are three wires going to the fan motor from the control box. Two are B and one is Orange.
One or the Black goes to the terminal F of the dual capacitor,the other to the load side of Line 2, and the Orange goes to the load side of Line 1. No resistance measured from ground to the disconnected terminal of each wire (done while all 3 were disconnected)

Wire to wire. No resistance was measured from B to B. 52.0 ohms was from Orange to the B wire detached from terminal F of the dual capacitor. 23.4 ohms measured from that Orange wire to the B off of the load side of contactor line 2.

I am using the service information and wiring diagram found at http://www.completeh...anuals/HS24.pdf

Edited by klawleman, 05 August 2011 - 05:20 PM.


#9 ACtechGUY

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Posted 05 August 2011 - 09:53 PM

Wire to wire:[/size]B to Y: 1.9 Ohms
B to larger R: 1.6 Ohms

Y to same R: 3.1 Ohms]

EXCELLENT!! . The resistances indicate the compressor is still electrically ok

[here are actually 5 wires going to the compressor; a black, a yellow, and three red. One red is the same gauge as the black and the other two red are smaller

The wires that power the compresor are the black , yellow and the larger red wires . The 2 smaller red wires are the crankcase heater.

You measured no resistance on the crank case heater, so it is safe to say that it is failed (HR-1 on your diagram) . Disconnnect those 2 small red wires and try to restart the unit. That may be your problem. A crankcase heater is a resitance coil that will read in the hundreds of ohms if good. This device can short to ground very easily. It is the thing you see wrapped around the bottom of the compressor or it may be inserted into the bottom of the compressor. There are wirenut or crimp connections under the compressor terminal box cover(AT THE COMPRESSOR)



Singnal wires from house:What I had called a B wire is actually pig tailed to a very light gauge white wire. That B wire goes to the coil terminal of the contactor's line 1 side. It measured 26 Ohms resistance to ground.

The Y wire actually pig tails to a light gauge R from the house and that Y goes to the contactors L2 coil. Measuring from its isolated terminal to ground I get 1.4 ohms.

Doesn't matter -- forget about the control circiut from inside. it has no bearing on your problem.


Two are B and one is Orange.[/size]]

Actually, it is Black PURPLE and orange. It has been that way since the begining of time itself.............


Wire to wire. No resistance was measured from B to B. 52.0 ohms was from Orange to the B wire detached from terminal F of the dual capacitor. 23.4 ohms measured from that Orange wire to the B off of the load side of contactor line 2.

OK now that is a problem, you should read resistance wire to wire on all wires . Try this. Compleatly disconnect the fan motor . Then try to restart the condenser. if the compressor starts and breaker doesn't trip you have found your problem . A failed condenser fan motor. don't run the unit for long without the fan motor.

#10 klawleman

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Posted 05 August 2011 - 11:16 PM

I disconnected the wires taking power to the compressor and the fan ran without opening the CB. The fan motor may be old and tired, but I don't think that it is the immediate problem.

I then disconnected the three wires going to the fan motor and reconnected the wires going to the compressor. Same problem with the CB immediately opening whenI tried to start it.

I also cut off some badly fried disconnects and replaced them with new ones. They didn't make a difference but the old ones were really bad. Half the connect was erroded from heat.

One wire, the black going from the load side of line 2 to the condensor was so nasty that I left it disconnected and tried to start the thing. The CB didn't open, the fan slowly moved, but nothing started

Yes. Looking closely at the wires one of the blacks is indeed purple.

I disconnected the two small red for the crancase heater, and I see it on the wiring diagram, and it made no difference.

Tomorrow is another day. I think I may just get this old turkey in the air. I was careful today ohming the wires, but will take an even closer look at the PURPLE wire to the fan. Thanks. I think you are trying pretty hard to help me.

Edited by klawleman, 05 August 2011 - 11:39 PM.


#11 klawleman

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Posted 06 August 2011 - 01:12 PM

In daylight, that third fan wire is definitely purple. I have had people tell me for years I get some colors wrong.

I carefully read between the black and purple terminal to the fan motor and got 28.5 ohms. Why I got none before who knows; possibly corrosion on one of the terminals. I replaced that "disconnect" (to me the female half of a terminal junction) last night.

BTW, a couple of weeks ago the fan bearing was whining and I lubed it by trying to get 5 drops of 3 in 1 oil to seep down into what looks like a punch out on the top of the baring shield for a lube connection that was never attached. The whining immediately stopped. I don't think that is related to the problem and as I just noted, with power to the compressor removed the fan runs.

Edited by klawleman, 06 August 2011 - 01:43 PM.


#12 ACtechGUY

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Posted 06 August 2011 - 06:49 PM

I Would have to say we have zoomed in on the problem. You have a failed compressor.
You eliminated the crankcase heater ,
You proved that the fan motor still runs,
The only thing left in the circuit is the compressor.

Did you ever look under the cover of the compressor wires go into the compressor? That is your last chance for finding a grounded/ burnt wire . If you find nothing at the compressor terminals ..................... Well , it has to be the compressor.

Maybe your "inexpensive" meter is not good enough for finding shorts to ground.. Who knows...

One last thought, If you have a internally shorted compressor , you may also have burnt refrigerant. Take the cap off the refrigerant gauge port and press in the schrader valve real quick . Take a sniff. YOU WILL KNOW if it is burnt, there is no mistaking it . It kinda smells like burnt diesel exhaust . If it is not burnt it won't smell like much.


Good luck . Although Ii think it is time to raid little jimmy's college fund for a whole new system.

#13 klawleman

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Posted 06 August 2011 - 07:43 PM

Thanks ACtechGUY. I was thinking of investing in a better multi meter already. Nothing pro grade but I was looking at some for around $35. It is one tool that keeps on giving; not just to try to keep the old appliances limping along but installing things like ceiling fans and other lighting fixtures. I am also toying with the idea of rewiring my garage with a subpanel and 240.

I will try those last things, but even if Lazarus wasn't going to be resurrected who knows how much I may have saved on paying an service guy to come out and charge me who knows what, which I can put towards a new system if needed, and it may be after 20 years.

I get a new meter. Hoorah! You have a good weekend. BTW. I read some of your comments on other posts and I was impressed that you know your stuff.

#14 klawleman

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Posted 07 August 2011 - 12:18 AM

You measured no resistance on the crank case heater, so it is safe to say that it is failed (HR-1 on your diagram) . Disconnnect those 2 small red wires and try to restart the unit. That may be your problem. A crankcase heater is a resitance coil that will read in the hundreds of ohms if good. This device can short to ground very easily. It is the thing you see wrapped around the bottom of the compressor or it may be inserted into the bottom of the compressor. There are wirenut or crimp connections under the compressor terminal box cover(AT THE COMPRESSOR)


I got a new meter; a Commercial Electric knock off of a Green Lee. It is still an inexpensive one but it has audible tone and measures a few more functions. I believe it measures capacitance in nano farads. Anyway, it read 1.307 KΩ of resistance red wire to red wire. Cycling through fuctions I also got a reading of .585 Volts for what I think was capacitance (Arrow point against a vertical line).

As suggested, I also took the fan motor and assembly off and opened up the compressor blanket. I popped the plastic cover over the terminals and everything looked good. I only had time so far to check for shorts on the three wires and tomorrow will remeasure the wire to wire.

I exposed the point where the crankcase heater enters the capacitor and it looked fine. The wires do not appear to be detachable there. The wires coming from the heater appear to be fastened to the the small red ones coming from the control box by a kind of crimp encased in foam. Nothing looked bad but I will take a closer look in the a.m.

I am thinking more and more a weak circuit breaker. It is a 50 while the side of the compressor cabinet says a 70 can be used with it. Of course, it may not be safe to go with a 70 depending on the rating of those house lines. If I replace the CB it will be with another 50A.

Edited by klawleman, 07 August 2011 - 12:36 AM.


#15 klawleman

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Posted 07 August 2011 - 03:22 PM

I measured the capacitors with my new meter. The start capacitor and the common to hermes side of the dual measured less than 2 nano Farads, while the common to fan terminals of the dual measured 10.41 microFarads. The fan does run with the compressor disconnected. I don't know the what either is rated.

As of now I know the ratings of the capacitors. The dual run is 60/10MFD and 330VAC. The start is 330VAC 189-227 MFD. The Big Question is if they are bad because the compressor is shot or if the compressor will be all right after I replace the capacitors.

Edited by klawleman, 07 August 2011 - 08:40 PM.


#16 ACtechGUY

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Posted 10 August 2011 - 10:39 PM

A bad capacitor WILL NEVER pop a circuit breaker instantly upon powering the unit. The end. No exceptions.

If however the compressor makes a "HMMMMMMMM" noise for a moment or two and then pops a breaker, It is very possible you have bad capacitors. You however did not mention a hum or a delay between powering the unit and the breaker tripping. It is also possible that you have a locked up compressor.



DID you measure the caps with the wires off???? Readings are meaningless if the wires are still on the capacitors. if the wires are off the readings you posted indicate failed caps.





#17 klawleman

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Posted 13 August 2011 - 06:36 PM

A bad capacitor WILL NEVER pop a circuit breaker instantly upon powering the unit. The end. No exceptions.


In so many words,that is what a neighbor with an AA in electrical engineering who is retired from selling wire, transformers, and elecrical components said.

If however the compressor makes a "HMMMMMMMM" noise for a moment or two and then pops a breaker, It is very possible you have bad capacitors. You however did not mention a hum or a delay between powering the unit and the breaker tripping. It is also possible that you have a locked up compressor.



You got it right. Their was no hmmmmmmmmm and the breaker tripped instantaneously. My engineering buddy also considered a frozen motor and ruled it out.

DID you measure the caps with the wires off???? Readings are meaningless if the wires are still on the capacitors. if the wires are off the readings you posted indicate failed caps.


Yes. With wires off. The only capacitor that did not measure to its rating was the hermes side of the dual capacitor and I replaced that with a new one.

I am now getting some very different readings on the compressor windings. These were taken from the ends of the wires with all three disconnected from terminals in the control box, but than I also took them directly from the terminals on the compressor (with all wires disconnected).

All these measurements were carefully taken with my new Klein multimeter during daylight when I could be certain that my probes were making good contact. Also, I could read where the terminals were marked with a C, S, and R.

C to S: 2.7 Ω (fluctuates as low as 2.6 and as high as 2.8)
C to R: 3.3 or 3.4 Ω
S to R: 4.6 or 4.7 Ω

I understand that SR should equal the sum of cs and cr, which would be 6 Ω.

Perhaps more telling is the reading I now am getting from pin to ground; 4.76 MΩ which slowly climbs in .01Ω increments. My little meter read this as infinity as did the Klein when I first used it. IIRC multimeters are not always sensitive enough to measure whether there is a short from a winding to the casing. Althugh I measured infinity before, there were momentary readngs that I subscribed to the meter settling to a range and number. Not so now.

Casing w paint scraped off or copper piping to any one of the three terminals reads 4.95 MΩ. (My old cheap pocket meter still reads infinity.)

Before I believe you always said it looked like a short in a winding. Given these new readings, does that now appear pretty definitiely the case?

I may not like what you tell me this means but I think we at last have what I call a positive reading

#18 RegUS_PatOff

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Posted 13 August 2011 - 06:42 PM

readings between C / S / R may depend on the accuracy of your OHM meter
digital or analog ?
did you check (or adjust) for "0" with the probes shorted together ?
Some meters are +-X% + 1 digit
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#19 klawleman

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Posted 13 August 2011 - 07:35 PM

This is a digital model MM1000 from Klein Tools that I only got last week. I don't see where it can be calibrated. I believe it calibrates itself when the probes are crossed. It sometimes first reads an ohm or less when they are crossed but it quickly goes to "000.0".

http://www.google.co...P&ved=0CBYQrhI#

#20 RegUS_PatOff

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Posted 13 August 2011 - 08:14 PM

The meter should be manually set to "manual" (not the default auto-ranging)
I don't know if that's a good meter to read less that 10 OHMs ..
Range . . . . .. . .Resolution . . . . Accuracy
400Ω . . . . . . . . .0.1Ω . . . . . . ± (1.0% + 5 digits)
the "accuracy" could add an extra .5 Ω to each measurement
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