Outside unit can't start. But try to start every 1 min


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Old 07-08-06, 04:53 AM
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Outside unit can't start. But try to start every 1 min

My AC is not working. The furnace part is fine. But the outside unit is not running. I heard it tried to start every 1 min ( it has the noise). Acturally the outside unit buzzed every 1 min tring to start.
Someone suggest it may be because of Contactor. Can someone tell me how to check it ?

Thanks.

Jeff
 

Last edited by jeffz; 07-08-06 at 05:23 AM.
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Old 07-08-06, 05:26 AM
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Any electrical device relies on two things in order to run. Volts and current.

Use a voltmeter to check for 220+ volts between L1 and L2 and then again between Load1 and Load2.

Use an amprobe to check the current draw on L1 then on L2. You should peg the needle during the start but settle down to around 35-45 depending on the size of unit, age, etc.

Usually, the symptom you describe is indicative of a self resetting switch. It could be internal to the compressor or on either the low or high side of the system. Does the fan run continuously or does it start and stop with the compressor attempts?
 
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Old 07-08-06, 05:28 AM
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Originally Posted by jeffz
My AC is not working. The furnace part is fine. But the outside unit is not running. I heard it tried to start every 1 min ( it has the noise). Acturally the outside unit buzzed every 1 min tring to start.
Someone suggest it may be because of Contactor. Can someone tell me how to check it ?

Thanks.

Jeff
I thought that part was called a capacitor? I'm not an expert but a capacitor went out on me once. Ok, here goes.

Remove the A/C side panel. The capacitor is the one that you see with coils of wire wound around it. It is like a magnet. When there's current going through it, it'll charge up and pull the capacitor contact in and thus completing the circuit. You can also manually push the contact it. Use a wooden stick or something just incase. But while it is trying to start (like you mentioned, every min or so), observe and see if this is the part that is moving.

In my case, the capacitor was bad and it doesn't hold enough charge to pull the contact in.
 
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Old 07-08-06, 05:34 AM
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Originally Posted by hamproof
I thought that part was called a capacitor? I'm not an expert but a capacitor went out on me once. Ok, here goes.

Remove the A/C side panel. The capacitor is the one that you see with coils of wire wound around it. It is like a magnet. When there's current going through it, it'll charge up and pull the capacitor contact in and thus completing the circuit. You can also manually push the contact it. Use a wooden stick or something just incase. But while it is trying to start (like you mentioned, every min or so), observe and see if this is the part that is moving.

In my case, the capacitor was bad and it doesn't hold enough charge to pull the contact in.
No, that's called the contactor. It could be restricting current enough so that the compressor does not have enough current to start, so replacing it might solve the problem...

The capacitor is a silver cylinder, maybe round or oval, with two or three terminals on the top. Possibly with multiple wires on some terminals. It stores energy in high amounts and releases it on demand of the compressor or fan start up.
 
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Old 07-08-06, 05:35 AM
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The Fan is not ruuing at all

It buzzed an try to start. The sound last about 3 seconds. After that, nothing happened. The fan is NOT running all the time.
 
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Old 07-08-06, 05:52 AM
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Then I would look to the contactor. They are less than $25 and would likely fix the problem. It controls both the fan and compressor so you should be getting the same type symptoms from both.

*Possibly* you can use an insulated screwdriver and manually hold down on the contactor but that is dangerous for the non professional...and not even recommended for the pro. But it might start up the unit and tell you for sure that it is the contactor. However, if it does not start the unit it is still not conclusive that the contactor is not the problem... I'd change the contactor... especially if you can watch the contactor and there is no evidence of it making attempts to make and break. If it looks like it is attempting to make and break we will look elsewhere for the problem.
 
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Old 07-08-06, 06:01 AM
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Mdtaylor - thanks for the clarification. FWIW, I had a HVAC contractor looked my non-functioning A/C unit. This was an industrial A/C unit located on the rooftop powering a restaurant I had before. He has been in business for 20 some years. I know we should always exercise caution but I swear he was pushing in the contactor manually w/ his fingers. He gave me a lesson on how these things work and attempted to teach me how to read the wiring diagrams etc etc. The A/C unit he was checking out was not working coz' the contactor had gone bad AND the wiring was all messed up (from the previous tech who serviced the unit before I took over the lease).
 
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Old 07-08-06, 06:05 AM
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Originally Posted by hamproof
I know we should always exercise caution but I swear he was pushing in the contactor manually w/ his fingers.
Yeah, we all do it...but don't admit it, :mask:
 
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Old 07-08-06, 06:08 AM
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Jeffz: Before replacing anything, you need a multi-meter to make a couple checks. That humminig sound you hear every minute or so sounds like the contactor is made and the compressor is humming and then clicking out on overload. Which could be a bad dual capacitor since the fan is not coming on either.

What make and model is the unit ??
 
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Old 07-08-06, 06:10 AM
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Depending on the type of contactor used, some can be activated manually safely, others are called "open faced contactors" and unless you know what you are doing, you can kill yourself very easily.

If you are unfamiliar with the equipment, it should not be attempted by a lay person.

The try to start problem. I believe it sounds more like a capacitor. When it tries to start then kicks out after the three seconds, what I believe is happening is the thermal overloads withinn the compressor is kicking out. The fan would not start either if this is a dual rated cap and the entire thing is bad.

Either tht or the compressor is toast but since the fan is not starting wither, I would think that there is a three term cap that is bad so neither would run.

like mdtaylor stated befor, the cap is round or oval and usually silver. There is another type that is dark (brown or black) that may be there as well. This one is also round.

See what you have and how many terminals and wires go to the thing.
 
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Old 07-08-06, 06:59 AM
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The model is Carrier 38CKB030300

I opened the side panel and pressed the contactor button . It gave me the same sound I heard before ( 3 seconds every 1 min). But the unit didn't start when I press down the contactor. Is it normal ? the cap is round and silver. Shound I replace the cap ? I have meter to measure, shoul I check something first ?

Jeff
 
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Old 07-08-06, 07:02 AM
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With the unit calling for cooling and the contactor pulled in, simply check between L1 and L2 and confirm you have 220. If so replace the capacitor.
 
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Old 07-08-06, 08:44 AM
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It is proved that the cap is bad. ( I have 2 A/C units, I switch the caps, the good and bad switches). Where Can I buy the caps ?

Thanks for the help
 
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Old 07-08-06, 08:50 AM
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Wink

Any Electric supply store or HVAC shop you find open today. Take the old one with you. Be sure turn power off and mark all wires how they go

ED
 
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Old 07-08-06, 09:41 AM
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And don't touch the terminals. They still hold electricity in massive amounts even after disconnected.
 
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Old 07-08-06, 09:57 AM
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Originally Posted by mdtaylor
And don't touch the terminals. They still hold electricity in massive amounts even after disconnected.
OH, the horror stories that statement brings up!!

One quick one:
A lot of you guys are too young to remember points and condensors in cars but the condensor is actually a small cap. We used to charge those things up on the plug wires and "toss" them to an unsuspecting friend. The resulting "snap" sound immediately followed by the look of surprise turned quickly to, "I'm going to kill you " look was "priceless".

While it no longer contained electrical energy, the kinetic energy involved with throwing it at your head was enough to hurt just as much.
 
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Old 07-08-06, 11:13 AM
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A happy ending

Thanks all of your supports and kindness. I bought a new cap replaced the bad one. The AC unit works well. Life goes back to normal .

Have a nice weekend.

Jeff
 
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Old 07-09-06, 07:28 AM
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Good fix.

*Side note: Yes Nap I remember those. Had an old mechanic once back in the 80's when I worked at a service station as a teen toos me one. Scared the baggebees out of me.
 
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Old 07-09-06, 09:56 AM
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Lightbulb Fan motor out? Cap is good?

Originally Posted by nap
The fan would not start either if this is a dual rated cap and the entire thing is bad.

Either tht or the compressor is toast but since the fan is not starting either, I would think that there is a three term cap that is bad so neither would run.
I assume that a dual duty cap that has 3 terminals (with one labeled fan with brown wire), and runs both the compressor and cooling fan; that if the cap was bad then neither the compressor or fan motor would run. And that it's not possible for the cap to only go "half bad" to allow the compressor to run, but not the fan motor. Is that correct?

If so, then my dual motor cap is just fine since my compressor will run, but the fan motor does not. Was working yesterday and then last night it died. First I thought it was the cap because neither fan motor or compressor would turn on. But that was because the compressor was too hot and when I got up this morning it was cool enough to turn on, but I turned it off when the fan motor did not come on.

So my conclusion is that the fan motor is toast and I need a new one. Any comments on my conclusion? This forum is incredible by the way.
 
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Old 07-09-06, 10:34 AM
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xenon2000

that if the cap was bad then neither the compressor or fan motor would run. And that it's not possible for the cap to only go "half bad" to allow the compressor to run, but not the fan motor. Is that correct?
You sure can have just on side go out and just the fan run or just the compressor. Can be the fan motor-- but Id check the big cap. first

ED
 
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Old 07-09-06, 10:49 AM
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Originally Posted by Ed Imeduc
xenon2000

You sure can have just one side go out and just the fan run or just the compressor. Can be the fan motor-- but Id check the big cap. first

ED
Thanks for the clarification. I was going to post an image, but I don't see a way to do attachments. Says I can't post attachments.

But I am sure it's a normal dual motor cap. It's a round cylinder silver cap that is about 5-6 inches long with 3 terminals on 1 end. Multiple yellow wires on 1 term, multiple blue on another term, and 1 single brown wire on the last term labeled "fan". Fan motor has Black, Yellow and Brown wire.

So you are saying that the Yellow and Blue wire terms are working fine, but that the single brown fan motor terminal section of the cap can be bad?

Is it normal for there to be 120volts on all 3 terminals when both motors are off?

Also, is it possible to test the fan motor by either using the other half of the cap in place of the compressor motor? Or some other way to test the fan motor without a cap? I would rather test the motor instead of the cap. But if that is not possible, is there an accurate way to test the cap before I buy one? It's Sunday, so I have to wait until tomorrow to buy anything anyways. Can't seem to find any HVAC parts outlets open on Sunday.
 
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Old 07-10-06, 09:11 AM
xenon2000
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Well, since I was told that part of a dual cap can be bad and not just the whole thing. I just used a spare 5uf motor cap that I had as a spare.

So I left the compressor on the 40uf section of the dual cap and then put the fan motor on it's own single 5uf cap. Works great. Now I have time to order a spare 40/5uf dual cap and keep my spare 5uf and keep this old dual as a spare 40uf cap and mark the 5uf section as bad.

Thanks for the great thread.
 
 

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