Another lost neutral

[growler]

Went on a call yesterday where the problem was an open neutral. It was a power company problem as their cable had the open.

Here is the question. Open neutral may have caused the AC compressor to burn/short. May have been a coincidence.

It was a Lenox unit and only a couple of years old. High efficiency unit with speed controlled compressor. An HVAC tech was there and he seem to think that a lost neutral would effect the control module for the compressor.

Anyone ever seen or herd of a lost neutral causing an AC compressor to lock up and short out. I would have figured that the controller board in the air handler would have burned and shut the unit off during a power surge like that but would like other opinion or comments.

 

[ActionDave]

AC unit is 120V?

 

[growler]

AC unit is 120V?

No it was a 5 ton 240 volt unit. The only 120 volt on the system would be at the air handler and normally their is a transformer to drop that down before the controller board.

 

[ActionDave]

So according to the HVAC guy a lost neutral is frying a 240V motor on a piece of equipment that doesn't use a neutral?

I'm not in a position to argue with anyone that is on site but I don't know about that.

 

[Hv&Lv]

When we have claims for this and it is deemed our fault (which is rare) it is always 120V appliances, TVs etc.
NEVER paid a claim for a 240V appliance.

Was it it just a bad connection at the weatherhead? Old aluminum split bolt connectors?

 

[growler]

When we have claims for this and it is deemed our fault (which is rare) it is always 120V appliances, TVs etc.
NEVER paid a claim for a 240V appliance.

Was it it just a bad connection at the weatherhead? Old aluminum split bolt connectors?

The bad neutral was caused by a tree limb rubbing the neutral conductor ( I guess as the wind blows). That's what the lineman that did the repairs said.

We didn't have that much of a loss from appliances only a cable box. Before I left the TV and the microwave was back up and working. They were real lucky on that one. I shut power off as soon as I checked ( about 5 minutes ) and figured the problem was a bad neutral.

The only thing I can't figure out is what happened to that AC unit. It just doesn't make sense. I have been reading a bit and that Lenox unit does have a more sophisticated control than a normal AC unit (because of the different speeds that the compressor can run). A friend of mine that's an HVAC contractor is supposed to go by and check it out and see if there are really $4K of repairs needed (estimated repair cost and that's just labor as the parts are under warranty ). He said it didn't sound right to him either.

Other than the AC unit cost would be minimal and not worth worry about.

I don't pretend to know everything but I have never seen an AC compressor (240 V circuit) damaged by a lost neutral.

 

[growler]

When we have claims for this and it is deemed our fault (which is rare) it is always 120V appliances, TVs etc.
NEVER paid a claim for a 240V appliance.

I don't think they would have much of a claim against the power company since trees on private property are the homeowner's responsibility . I'm not sure just how many homeowner's are aware of this. You see power lines running through trees all the time.

 

[gadfly56]

I don't think they would have much of a claim against the power company since trees on private property are the homeowner's responsibility . I'm not sure just how many homeowner's are aware of this. You see power lines running through trees all the time.

AFAIK, the POCO is responsible up to the weather head, regardless of who owns the trees.

 

[qcroanoke]

AFAIK, the POCO is responsible up to the weather head, regardless of who owns the trees.

+1
Its been awhile but when I was doing tree work around power lines POCO had a 20 ft right of way from the lines.

 

[PaulMmn]

I don't think they would have much of a claim against the power company since trees on private property are the homeowner's responsibility . I'm not sure just how many homeowner's are aware of this. You see power lines running through trees all the time.

Along the rights-of-way the POCO will come by and either prune a tunnel through the branches, remove half of the tree to avoid the wires, or remove the tree entirely. So the POCO does have some responsibility... at least up to the point where the homeowner's tap begins.

 

[Hv&Lv]

AFAIK, the POCO is responsible up to the weather head, regardless of who owns the trees.

Nope. We don’t have right of way for secondary cables.
They are the customers trees.
I don’t know of a POCO around that could afford to cut trees for every secondary cable on their system.
Primary and transmission is different.

 

[mbrooke]

Is the AC unit 120/240 by chance?

 

[growler]

Is the AC unit 120/240 by chance?

No. 240 V.

That's what doesn't make sense.

 

[growler]

AFAIK, the POCO is responsible up to the weather head, regardless of who owns the trees.

The power company will repair their cable when damaged at no cost to the customer. But trying to get any damages out of them for damage done to appliances because of a lost neutral is another thing.

 

[mbrooke]

No. 240 V.

That's what doesn't make sense.

Was just the neutral in the drop damaged or the phases? If a phase was intermittently open or shorting to neutral, the fluctuating L-L voltage could've kept stalling the compressor after it started.

More likely the fluctuating voltage at the 120 volt air handler was causing the AC contactor to keep dropping in and out.

 

[growler]

More likely the fluctuating voltage at the 120 volt air handler was causing the AC contactor to keep dropping in and out.

That makes more sense than anything else that I can think of.

With a lost neutral we tend to only think of the effects of power surge on the phase that goes high with the potential to damage equipment but having the other phase go low could also cause a problem with something like an AC unit.

 

[Hv&Lv]

That makes more sense than anything else that I can think of.

With a lost neutral we tend to only think of the effects of power surge on the phase that goes high with the potential to damage equipment but having the other phase go low could also cause a problem with something like an AC unit.

Normally the fluctuations in the L-L voltages shouldn’t affect the 240V loads, like you stated earlier.
Depending on what single phase loads are trying to start, the line voltages could shift to 0 on one leg and 240 on the other leg.
still shouldn’t bother the compressor.
I agree with you, looks like a board or some other component would be shot, but not a compressor lockup.
i don’t see how the air handler running or not running will cause a compressor to lock up. I can see it controlling the compressor either off or on, but not lock up.

unless...

the board that controls the compressor start delay was shot, and the compressor didn’t get a delay signal... that I could see.
but I thought the board was 24 VAC...

speculation... I’m not an AC guru.

 

[mbrooke]

That makes more sense than anything else that I can think of.

With a lost neutral we tend to only think of the effects of power surge on the phase that goes high with the potential to damage equipment but having the other phase go low could also cause a problem with something like an AC unit.

Yup. And think of something like a 120 volt refrigerator. The compressor can trip on its over load causing the other leg to rise high, and then when the overload closes the voltage on the other leg will then plummet. You can get a see-saw like effect where both legs are alternating high-low-high-low relative to each other.

 

[kwired]

Was just the neutral in the drop damaged or the phases? If a phase was intermittently open or shorting to neutral, the fluctuating L-L voltage could've kept stalling the compressor after it started.

More likely the fluctuating voltage at the 120 volt air handler was causing the AC contactor to keep dropping in and out.

+1

I don't know what OP has for "speed control".

Only true VFD units I have ever seen were three phase input and was a complex system with multiple indoor units - the compressor unit was the master unit on that system.

I have seen "two stage" units in dwellings, but compressor motor still runs at full voltage and frequency, in those the second stage just kicks on some solenoid valve to change refrigerant flow in that stage which results in less overall output in that mode.

If this damage was caused by lost neutral on the system it had to happen via the controls that originate from the 120 volt master unit. On/Off signal not so much a problem, rapid cycling can be, though most units have anti-short cycle timers anymore and that makes that possibility less likely also.

 

[growler]

Yup. And think of something like a 120 volt refrigerator. The compressor can trip on its over load causing the other leg to rise high, and then when the overload closes the voltage on the other leg will then plummet. You can get a see-saw like effect where both legs are alternating high-low-high-low relative to each other.

One more thing I should mention about this problem. The AC unit did make some strange noise ( home owner thought it was the fan bearings or something) and it tripped the 50 Amp breaker. He said that he tried to reset the breaker but he may have reset it until it would no longer function.

I didn't get there until 11 AM the next morning and the power was still on. When I checked and confirmed a bad neutral I shut the power off so as to do as little damage as possible. But after power was restored (around 1 PM) and the AC guy showed up we tried to turn on the AC and the breaker was bad and would not reset.

Normally my job would be over as I don't get involved with AC problems. The HVAC tech that showed up gave and estimate of over $4 grand in labor to repair the problem ( parts still under warranty). I suggest that the home owner call a friend of mine to get a second opinion on cost as this seemed a little high. My friend said the job should only take about a half day (actual work time not counting time to get warranty parts).

Since I have never seen an AC unit damaged like this due to a lost neutral it has kind of got me interested. Even we old dogs have to learn a new trick now and then.

I have been reading a bit and have learned that Intermatic even has a surge protector for just an AC compressor that may be worth looking into
( the AG3000). If it's going to cost that kind of money just to replace a unit compressor you would want to protect it as best you can.

I have also learned that I wouldn't buy that particular unit as it's known to have bad condenser coils that need to be replace often. People really need to do their research before making any major purchase these days.