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Discussion Starter · #1 ·
I have a problem that I would like some additional help on.

My AC works fine when it is dry out. I've had a tech out here just two days ago to confirm that my coolant levels are good, the compressor works fine and gives me appropriate pressures, power draw is within spec, I'm not icing up the evaporator, and I'm getting a normal air temperature differential across the evaporator. In other words, the system works.

However when it rains, the system stops cooling. I get warm air out of the register and the compressor unit outside stops rejecting heat (it's just blowing air through the fan, but the air is not appreciably warmer, as it should be) while the fan continues to run. Usually it takes half a day or more of letting the system sit idle after rain stops before the system will blow cold air again. On more than one occasion, the system has gotten to this state and continued to run, only to eventually trip a breaker at the air handler.

I suspect this is some sort of electrical problem, but I need more information or to hear from someone who knows more about this stuff.
 

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I would have your contractor return and inspect and test wiring. Possible to have something bare and shorting due to water.
 

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can you yourself check the evap coil? If so, I would check it while this is happening. I suspect your evap coil may be freezing up when the rain acts as an additional heat transfer medium, which is more effective than the air, and causing the evap coil to freeze up.

Instead of waiting for the rain, I would think a sprinkler would simulate the rain.

a dirty evap coil will is also more prone to freezing up as well so if the evap coil is dirty, this would add to the situation.
 

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If the breaker tripped one time I would start looking at the electrical connection between the disconnect and condenser. I would also inspect the low voltage wire from the furnace to the condenser.

When you start to inspect the electrical connection make sure you turn off power to the condenser. If the is a bare wire or short you don't want to be the newest short to ground.
 

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Discussion Starter · #5 ·
If the breaker tripped one time I would start looking at the electrical connection between the disconnect and condenser. I would also inspect the low voltage wire from the furnace to the condenser.

When you start to inspect the electrical connection make sure you turn off power to the condenser. If the is a bare wire or short you don't want to be the newest short to ground.
I'm real good with industrial safety since I started my professional career as a nuclear power plant non-licensed operator. I basically do my own home red-tagging program, and do live-dead-live testing on electrical stuff I work on. :)

I pulled the side panel off of my outside unit and I may have found some corrosion on the main power relay to the compressor, but the wiring looks good otherwise. I'll keep you all posted after I clean this bit up. I'm going to have to bring it inside.
 

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You may have a contactor going bad
 

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Discussion Starter · #7 ·
Well, that didn't change anything. The contactor works fine, the resistance across it was less than 1 ohm, and it shut clean when the demand signal to start the outside unit came on (after I had re-installed it).

The unit still is not rejecting any appreciable amount of heat, though, and thus not cooling. This is really puzzling. :censored:
 

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Discussion Starter · #8 ·
can you yourself check the evap coil? If so, I would check it while this is happening. I suspect your evap coil may be freezing up when the rain acts as an additional heat transfer medium, which is more effective than the air, and causing the evap coil to freeze up.

Instead of waiting for the rain, I would think a sprinkler would simulate the rain.

a dirty evap coil will is also more prone to freezing up as well so if the evap coil is dirty, this would add to the situation.
The one time I crawled under the house and opened the panel on the air mover (right after I had shut the system down during one of my investigations), I found the evaporator wet but not frozen. The condensate drain line was also clear, and no water was pooling. The evap was pretty clean, also.

I really hope this doesn't come down to TEV or compressor replacement, but what gets me is the whole business about the system failing ONLY when it rains.
 

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What I thought when I first read this thread was the maybe when weed eating you might have nicked the low voltage line and when it rains some how they are shorted together causing just enough voltage lost and not pull in the contactor.

Does the condenser come on and run when the concern is happening?

If it is

I'd want to know what the amps reading to the condenser is when this is happening. Low amps=fan running High amps=fan/compressor running

Want to know if the compressor is running or not.

To me this is an outside wiring issue
 

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Discussion Starter · #10 ·
What I thought when I first read this thread was the maybe when weed eating you might have nicked the low voltage line and when it rains some how they are shorted together causing just enough voltage lost and not pull in the contactor.

Does the condenser come on and run when the concern is happening?

If it is

I'd want to know what the amps reading to the condenser is when this is happening. Low amps=fan running High amps=fan/compressor running

Want to know if the compressor is running or not.

To me this is an outside wiring issue
Unfortunately I do not have the inductive ammeter that the recent tech did. My multimeter can't handle that sort of amperage.

The only indicator I have whether or not it's fan or fan/compressor is the heat rejection, and that's pretty easy to tell the difference on. When the tech was out the other day and the unit was properly rejecting heat, it was drawing about 10 Amps.

I think it is safe to assume that the compressor is not running, based on the lack of heat rejection. At least that's what I have to go on until I can purchase or borrow an inductive ammeter.

I'll get out there tomorrow when it's daylight and have a session with the wiring diagram, following the wiring to look for anything erroneous.
 

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doubt it is the wetness of the rain i think it is more the temperature drop with the rain cooling the condenser.might want to check the stat for comptressor on/off time adjustment...you might be short cycling the compressor after the last run and the pressures haven't equalized so it goes to restart and trips the breaker.the flag there is that the condenser fan is running but the compressor isn't... you have only one contactor that powers both on a call from the stat so the compressor is going off on internal limit with that short cycle.if your stat has no configuration for compressor on and off cycle you can add a adjustable time delay out on the condenser control wiring going in. http://bestbuyheatingandairconditio...duct_Code=REL203AA&Category_Code=r-compressor
 

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No body get's it:huh: During a rain shower the weight of the water slows down the cond fan mtr. Cond fan is weak.
 

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No body get's it:huh: During a rain shower the weight of the water slows down the cond fan mtr. Cond fan is weak.
that should not appreciable change the cooling ability of the system though since if there is that much water, the cond coils would be getting washed down with the rain as well. Additionally, it takes 1/2 day or more on non-use to rectify.


For some reason, I figured the OP knew if the compressor was running or not. Apparently my mistake. Unless you have a very quiet compressor, you should be able to tell if it is running or not.

If the comp is not running, then, to me, it could be something along the lines of what plumber was shooting at or even what biggles was aiming for.

emfuser:

can you operate the unit with the cover off and observe the compressor. Even without a ammeter, you should be able to tell if the comp starts or not.

You can place a hand on the comp and tell if it is running. Safety check possible circuit pathway for shorts first though.

If the comp is not running, you need to determine why.

Is power reaching the comp? If so, a bad comp or a bad Klixon switch or bad capacitor. Biggles hit on something there as well. If a bad comp or bad klixon, or cap, a short cycle could cause a problem along these lines. If you have any of the noted problems, a short cycle may cause overload of the comp and any of the three could cause a no comp start.



Bottom line; you need to be able to determine if the comp is running and then attempt to repeat the scenario while observing.

biggles; the fact it takes upward of 1/2 a day or so would generally remove just a simple short cycle problem that a time delay would help with. There has to be a bad part to be causing long term problem such as this.

when testing I would look for an attempt to start and then comp shut down. Then, if it attempts again in a minute or so, I would look to a capacitor or a system problem allowing too high of head pressure or even liquid slugging.

If it does not try to start, I would look towards the klixon switch.


if all else fails; call an AC guy that knows more than simple gauge pressures. A "tech" that knows there is a problem under certain situations and only checks while things are expected to be working normally and leaves when things appear to be fine is not a tech.
 

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No body get's it:huh: During a rain shower the weight of the water slows down the cond fan mtr. Cond fan is weak.

I thought of the Been but I would think that it would have to be reduced by atleast 25% of more rpm to see what no cooling.

I mean I have seem as I'm sure you have seen where a condenser coil is so plugged that air flow is reduced but it still cools a little.

I'd like to put a set of gauges on and so the sprinkler thing someone here proposed
 

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Discussion Starter · #16 · (Edited)
nap, Thanks for the excellent post.

Not surprisingly, I got up this morning, flipped the AC switch to "cool", and the AC is working again (after being off for more than 12 hours overnight). So now I'm back to having a working system that I know will cease to cool the air as soon as it rains again (I live in South Carolina, so it can be almost daily at this time of year).

Is "klixon" a colloquial name for the solenoid-driven relay that feeds main power to the outside unit, off of the nearby breaker?

Other information that may be of use: This tends to happen while the system is in operation. As in the system will be running, a short strong rain comes through, and the system continues to run, but is producing warm air after not too long. The next time it rains when I'm home, I'll verify this.

In the time span of about a year or so, the breaker has only tripped twice, and it was the one labeled as "AC" (vs heater) which is actually on a breaker panel right next to the air handler under the house.

The lazy tech over here the other day noticed that, when the system was turned on, that it immediately went into delay (vs coming on immediately) when switched to "cool", even after the system had been shut off for hours, and that there was probably something unusual with my thermostat wiring or settings. I'm not sure if this is relevant, but I'll just put it out there.

Also, the electrical components mounted in the controls space on the outside unit were well-shielded from non-vaporous moisture, were dry when I took the panel off, and the components themselves looked to be in great shape. I couldn't see any capacitor swelling or leakage, nor any cold or sloppy looking solder joints, nor any rusty connectors or that sort of thing. It was remarkably unremarkable.

Thanks again for your help, everyone. I really appreciate it. :thumbup:

I know this is an odd problem. Nap, I will use your advice as a guide to check some stuff the next time this happens, as it has been happening quite reliably. I will, in the mean time, contact some different local HVAC contractors to see if they'll come out and help me troubleshoot this, rather than doing what the last tech did, which wasn't much.

I'll keep you all updated as I learn things and am always welcoming to new information.
 

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a klixon switch is the a mechanical overload that is attached to the compressor. It reacts to heat or by being heated. Some are visable on the outside of the comp case. Some are not.

they are quite similar to the thermal switches found in a furnace for high temp cut in and low temp cut out of the fan.

when the comp is overloaded, there is excess current draw and the motor for the comp heats up. This then causes the klixon to trip out. If it does not reset as it should or if it is weak, it would cause the comp to stay off beyond when it would normally reset or it could trip too quickly.

as to the time delay; not unusual. Some units delay every time they start. Some delay only when restarted within a determined period of time of shutdown. I would not be overly concerned unless it could be proven that it was simply causing the comp to never start for some reason. So, a question to that; when in delay, is the fan delayed too or just the comp? If it is fan also, this would remove the delay as a problem since the fan is running even when having this problem.

If it is comp only, then more investigation is needed.

to the capacitor; caps don't alway look bad when they go bad. Sometimes the simply lose capacity. Unless you have a cap checker on your meter, you will not be able to determine if this is the case. You can do a basic check on a cap with a voltmeter and an ohmmeter but that will not provide an actual cap rating, which would be needed here, IMO.
 

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a klixon switch is the a mechanical overload that is attached to the compressor. It reacts to heat or by being heated. Some are visable on the outside of the comp case. Some are not.

they are quite similar to the thermal switches found in a furnace for high temp cut in and low temp cut out of the fan.

when the comp is overloaded, there is excess current draw and the motor for the comp heats up. This then causes the klixon to trip out. If it does not reset as it should or if it is weak, it would cause the comp to stay off beyond when it would normally reset or it could trip too quickly.

as to the time delay; not unusual. Some units delay every time they start. Some delay only when restarted within a determined period of time of shutdown. I would not be overly concerned unless it could be proven that it was simply causing the comp to never start for some reason. So, a question to that; when in delay, is the fan delayed too or just the comp? If it is fan also, this would remove the delay as a problem since the fan is running even when having this problem.

If it is comp only, then more investigation is needed.

to the capacitor; caps don't alway look bad when they go bad. Sometimes the simply lose capacity. Unless you have a cap checker on your meter, you will not be able to determine if this is the case. You can do a basic check on a cap with a voltmeter and an ohmmeter but that will not provide an actual cap rating, which would be needed here, IMO.
First off i don't if you are aware that a Klixon has not been used on residential compressors for the last 30 years. The OL and over temperature protection comes from a thermistor buried in the motor windings which is of the inhereant type.


Secondly the rain failing on to a condenser will hardly suffice to cool the discharge gas going into the condenser. Water cooled pkg ac units measure water flow in gallons per minute to cool the compressor and the condenser.

No normal rain fall is going to suffice cooling a forced air condenser.

And further more the majority of the rain will flow over the the condenser fins with very little coming in connect with copper tubing. In fact the rain running down the the finned surface will act as eliminators do in an evaporative condenser and try to re-evap the water, which can not be accomplished as the RH is at 100%.

A borderline condenser fan motor is a very likely candidate. It will stick when over heated and after being off as the OP describes will operat normally.

Why does it do it on a rainy day but not on a sunny hot day?

Amp draw. Running while the rain falls forces the fan to work harder and grow hot. And some condenser fan motors are overload protected by a Klixon or some other type or brand of like protection.

Klixons were famous for cracking the bi-metal of the motor they protected
and would operate intermittently. But again I must reiterate that compressor for residential comfort cooling do not use Klixons.

Until the OP get's a confirming opinion none of us will know for certain what the problem actually is. But some of the opinions set forth here will be much closer than others.
 
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