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leibold
Premium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:10
Reviews:
·SONIC.NET
reply to robbin

Re: [HVAC] Condensing unit problems

A slowly / erratic running fan motor while the contactor is in the OFF position may be the result of a motor winding short-circuiting to ground. This happens only with single pole (or 1.5 pole) contactors since only one of the two hot legs is actually shut off.

I found that out on my own AC unit.

A competent HVAC repairman would be familiar with the fairly common single pole contactors and the fact that the condensing unit remains energized (one hot leg) even with the contactor being OFF.

Farley, while I don't always agree with Jack (and fully disagree with him on infinite ohms on multimeters), he is correct to warn you about the qualifications of your repair person.
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robbin
Premium,MVM
join:2000-09-21
Leander, TX
kudos:1
said by leibold:

A slowly / erratic running fan motor while the contactor is in the OFF position may be the result of a motor winding short-circuiting to ground. This happens only with single pole (or 1.5 pole) contactors since only one of the two hot legs is actually shut off.

True, but that wouldn't explain the compressor not starting.

Regarding the repair person, I find totally understandable that when a new problem cropped up working for a friend after work at 10 pm and not having the parts they think are needed to pack it up for the night. As far what the tech thinks is wrong, the OP clearly does not have a working knowledge of the parts and what they are called so it is also understandable if we are not getting a clear accounting of what was said.

said by Farley11 :

The problem with him not fixing it last night was in my opinion because he was at my house until 10 pm fixing my original problem (he does this type of stuff after he leaves his full time job) and he didn't have the part with him to fix what he thinks is wrong with it.


walta

join:2001-05-22
Saint Louis, MO
kudos:2
reply to Farley11
Short cycling a compressor is very bad thing to do.

I think the fan is turning slowly because the compressor is not starting and drawing high current and lowering the voltage to the fan motor.

I agree that shutting off the power will not damage your compressor.

What can damage your compressor is restoring the power in the next 5 minutes.

If your unit has a piston compressor and it tries to start before the system pressure equalizes this can overload the compressor motor and trip the overload.

If you are very lucky turn off the unit for an hour and it may work if nothing was damaged only over heated. Not you this time.

Let’s hope the high start current from the short cycle killed a weak old start capacitor and it will be a cheap lesson for both of you.

The bad news the shock of trying to start the compressor with high head pressure jammed the piston and seized the compressor requiring its replacement.

Walta


cowboyro
Premium
join:2000-10-11
Shelton, CT
reply to Farley11
said by Farley11 :

He has never seen this before and he's did this for a living for over 20 years. He does not understand how the unit is still getting power when it is turned off.

Turned off as in breaker off or as in thermostat off? Because there is a big difference. And if the unit is getting power with the breaker off then either the correct breaker is still on or there is a major wiring issue in the house which requires a competent electrician ASAP.
And what is he using to check for power? Please don't tell me a digital multimeter....

LittleBill

join:2013-05-24
kudos:1

1 recommendation

said by cowboyro:

said by Farley11 :

He has never seen this before and he's did this for a living for over 20 years. He does not understand how the unit is still getting power when it is turned off.

Turned off as in breaker off or as in thermostat off? Because there is a big difference. And if the unit is getting power with the breaker off then either the correct breaker is still on or there is a major wiring issue in the house which requires a competent electrician ASAP.
And what is he using to check for power? Please don't tell me a digital multimeter....

exactly what kind of meter should he be using? a digital multimeter is more then correct to check for voltage presence

also most compressors have a limit switch to deal with a compressor lockup, that will drop out if it hits, they generally reset in minutes not hours, thus not damaging the compressor

what exactly do you do if the power goes out while its running? the unit just fries? no it just trips out

alot of weird help on this one

\


leibold
Premium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:10
Reviews:
·SONIC.NET
said by LittleBill:

exactly what kind of meter should he be using?

A high impedance digital meter may give the false impression of a voltage being present through inductive / capacitive coupling. A simple voltage tester is more useful in troubleshooting since its own load will cause that phantom voltage to collapse.

I'm still using an ancient Siemens voltage tester that looks very much like this one (different brand, different trigger voltage for the neon indicators). It has two LEDs to indicate the polarity of DC voltages or to indicate AC if both are lit. The neon lights give a rough idea about the voltage level.
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Tex
Dave's not here
Premium
join:2012-10-20
kudos:2

1 recommendation

reply to Farley11
said by Farley11 :

Just had the fan motor replaced by a certified repairman. Everything worked as it should and I asked him how loud it was when it came on because our unit is very close to our neighbor's bedroom window. While the unit was running, he pulled the breaker from the disconnect box and put it back in to show me how loud it was. Now the fan will slowly spin but the condesor will not come on. You can hear it trying to work for a split second then it fails. He was saying there was a some sort of overload trip meter thingy that won't trip back to where it should be. What are my options? He said let it sit overnight to see if it will cool off and come back on. This morning it was doing the same thing. When the thermostat is turned off, the unit is still receiving power for some reason and this has him scratching his head. I'm thinking that whatever piece of equipment stops the flow of electricity to the unit has failed and needs to be replaced. If I am correct, will this probably solve my problem?

Some of what I'm about to say has been said in one post or another, but I wanted to try to put it in one place, minus the criticism of your friend. I've been in his shoes before, so I know what he was going through. Even being a "certified" repairman, unexpected things can happen that can catch even the most experienced repairman off guard, especially that late at night.

One should never pull the disconnect on a running condensing unit and put it right back in without waiting at least five minutes. This gives the system time for the refrigerant pressures to equalize. A few things can happen. One, the compressor can overheat trying to start and trip out on its internal overload protection. Depending on how hot the compressor became, it can take hours for it to cool down enough for the overload to automatically reset. If the compressor is enclosed in a sound blanket, it can take even more time to cool down. Running water over the compressor can speed up the process, but not always. I've had more than one internal overload that wouldn't reset until the next day.

Two, when the compressor tried to start, doing so blew the run capacitor. As mentioned, the unit could have an individual run capacitor for the compressor and an individual run capacitor for the condenser fan motor. More than likely, the system has a dual run capacitor. I think that's the case in this situation because you mentioned the fan motor was spinning slowly after he tried starting the unit. (Hopefully, he installed the right motor and didn't mis-wire it.) So, I'm guessing you'll need a new dual run capacitor to get your system running again.

Three, and more seriously, the compressor motor windings were damaged to the point where the compressor will no longer run. Hopefully, this is not the case and it will need only a new capacitor.


Lurch77
Premium
join:2001-11-22
Oconto, WI
kudos:4
reply to Jack_in_VA
said by Jack_in_VA:

There is no such fault that "letting it cool overnight" will correct.

If he yanked the disconnect and tried restarting it right away, this does not allow pressure balance for a reliable start. The compressor likely tripped its internal overload. Only time to cool off will reset it. This is the reason for time delays, often called compressor protection on thermostats.

So letting it cool is a legitimate idea, if this was the problem.


Tex
Dave's not here
Premium
join:2012-10-20
kudos:2
Wouldn't you agree that having a time delay wouldn't have helped in this particular situation because the time delay, either part of the thermostat or separately installed in the condensing unit, wouldn't have kept the unit from trying to start? The time delay is wired through the air handler's or furnace's 24V circuit.


Lurch77
Premium
join:2001-11-22
Oconto, WI
kudos:4
Yes, agree with you 100%. I was only pointing out a situation where "letting it cool" is not necessarily BS. That the home owner is having issues the next days suggest more than just that has happened, though. You covered the possibilities well.


Farley11

@scansafe.net
reply to Tex
Thank you for your helpful reply. Time for an update and results for those following this thread.

First a little backstory. I have a Goodman 3 ton unit that is 10 years old. I've had to replace the capacitor twice and I guess it was time for something major to go out. I initially had him come out because the unit was making a loud buzzing noise every 60 seconds or so. By the time he got out to take a look at it, the fan had broken loose from its mounts and banged around the unit. He came out late the other night and replaced the capacitor, the contacts and the fan. We know what happened shortly after that. He came out yesterday while it was still light so he got a really good look at what was going on. He replaced the contacts again and that fixed the electric current problem. He ran some other "tests" and isolated the problem to the compressor motor. He told me what was wrong with it and that I needed a new one...I don't remember what he said because my eyes started spinning like a slot machine with dollar signs. Also while he was looking around he saw that when the fan broke loose, it caused some damage to the copper coil thingy that lines the inside of the unit. He said he had no way of knowing if the damage was enough to cause it to leak the refrigerant during the summer but he said there was a very good chance it would (I live in Texas). So I was faced with 2 options. I could either pay $800 for a new compressor with a 1 year warranty and risk the coils working properly (new coils cost $1300) in the summer or pay $1400 for a new unit with a 5 year warranty and sleep good at night. I obviously chose to pay for a new unit. He is giving me my money back on the parts he installed and is not charging me labor to put in the new unit.

Did my "friend" cause my compressor to go bad? Most likely but I look at it this way...before anything happened he warned me that the compressor was on its last legs and would need to be replaced soon and I would rather it happen now than in the middle of a Texas summer. Again the unit is 10 years old. I realize this event has costed me more than it needed to but there is no need to get bent out of shape over the past. There you have it folks.

walta

join:2001-05-22
Saint Louis, MO
kudos:2

1 recommendation

reply to Farley11
I hope your friend learn something even you are paying for his lesson.

The saddest thing would be if this situation cost you a friendship and money.

I hope the two of you can get past this.

Try to remember it easier to make money than friends.

Walta