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Old 06-14-2009, 09:57 AM   #16
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AC stops cooling when it rains


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.

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.


Last edited by Emfuser; 06-14-2009 at 10:02 AM.
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Old 06-14-2009, 10:30 AM   #17
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AC stops cooling when it rains


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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Old 06-14-2009, 10:32 AM   #18
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AC stops cooling when it rains


I have one more bit of advice:


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Old 06-14-2009, 11:12 AM   #19
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AC stops cooling when it rains


I've considered that too.

In the mean time, I'll check out your suggestions. Thanks.
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Old 06-14-2009, 12:02 PM   #20
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AC stops cooling when it rains


Quote:
Originally Posted by nap View Post
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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Old 06-14-2009, 03:02 PM   #21
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AC stops cooling when it rains


clover, point out the thermistor in this unit:

ac unit

there is none of the optional wirings installed.
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Old 06-14-2009, 03:12 PM   #22
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AC stops cooling when it rains


Quote:
=hvaclover;287300]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
.
what the heck is "inhearant"?

Quote:
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.
a sprinkler seems to work fine. Maybe that is more water than when it rains,

Quote:
No normal rain fall is going to suffice cooling a forced air condenser.
but it will slow a fan? and that fan being slow will cause the unit to not cool for 12 hours? as in total loss of cooling?

Quote:
And further more the majority of the rain will flow over the the condenser fins with very little coming in connect with copper tubing.
I suggest you have no idea what the fins are even for if you say things like this. Contact with the tubes is irrelevent. The fins radiate the heat.

Quote:
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%.
Uh, ya, sure, whatever you say. Water is a much more efficient means of thermal transfer than air. Evaporation is not needed here.

Quote:
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.
the only thing we know is the fan does not stop yet you maintain that it slowing, an unperceptable amount by the owner, that it would stop all cooling for 12 hours.


Quote:
Why does it do it on a rainy day but not on a sunny hot day?
suggestions were given. read them.

Quote:
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.
Ya, and if a Klixon or some other type of overload tripped, the fan would stop running. That is the one thing we know for sure is NOT happening.

Quote:
Klixons were famous for cracking the bi-metal of the motor they protected
and would operate intermittently.
cracking the bi-metal of the motor???? I can understand if you said, the bimetal thermal strip of the Klixon switch cracked and thereby causing intermittant and undependable operation but you said the metal of the motor cracked. I think you arecracked.

Quote:
But again I must reiterate that compressor for residential comfort cooling do not use Klixons.
Take a look at the pic and get back to me.


Quote:
Until the OP get's a confirming opinion none of us will know for certain what the problem actually is
Duh!!!

.
Quote:
But some of the opinions set forth here will be much closer than others.
Obviously and I would bet I know whose is nowhere near close (clover)
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Old 06-14-2009, 05:12 PM   #23
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AC stops cooling when it rains


My two cents, When it rains heavily, it wets the condensing coil dropping the pressure in the system. If the system is overcharged with freon the condenser may flood and slug the compressor with liquid refrigerant. The slugging overloads the compressor and the compressor shuts down on the internal overload protector. The overload may be faulty and sticks open and stays open until all of the heat is gone from the compressor. Could also be a weak capacitor or a combination of both. Just my two cents.
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Old 06-14-2009, 05:29 PM   #24
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AC stops cooling when it rains


Less than 30 mV across closed relay contacts at rated current is good, over 100 mV is bad.
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Old 06-14-2009, 05:50 PM   #25
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AC stops cooling when it rains


Skip, FYI and others the overload is a heat only activated device and trips when the unit is run out of freon and grossly overheated. Overload/overcurrent protection is done by the cicruit breaker. Slugging will wreck the valves and it won't ever pump properly again. Just trying to be educational. OP needs to by a amprobe clamp around the wire meter and check the amps when he thinks it is not cooling and let us know if the compressor is drawing amps. The cond fan motor draws very little. Just finished the mystery of the backwards running cond fan motor and now we have this one. Interesting.

Last edited by yuri; 06-14-2009 at 05:56 PM.
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Old 06-14-2009, 06:31 PM   #26
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AC stops cooling when it rains


Quote:
Originally Posted by yuri View Post
Skip, FYI and others the overload is a heat only activated device and trips when the unit is run out of freon and grossly overheated.
I have had them trip on hard start situations where there most definitely was not a lack of freon.
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Old 06-14-2009, 06:32 PM   #27
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AC stops cooling when it rains


what the heck is "inhearant"?

I misspelled
inherent
. It is(as applies here) the ability to sense amperage and heat and open to protect to protect the compressor from damage.

a sprinkler seems to work fine. Maybe that is more water than when it rains,

A sprinkler passes more water than rain. When it rains it is always less than an inch. When we get over five inches it causes floods.When was the last rain fall you saw that came down at the same pressure the city pumps water to your home. A sprinkler moves a lot more water than a normal rain fall.

That was a bad comparison you made


but it will slow a fan? and that fan being slow will cause the unit to not cool for 12 hours? as in total loss of cooling?


Either you are a DIY or you have not done much hvac work or you just like blowing smoke.

You cheery picked my last statement by leaving out the key phrase of the "weak condenser fan motor". Yes a rain will cause a weak motor to draw more amps and over heat and cut out (stop) on overload if it's so equipped.

If the condenser fan motor itself has a weak bimetal OL it could remain off for twelve hours as the weak or cracked bimetal would take that long to reset.







clover, point out the thermistor in this unit:

v
I suggest you have no idea what the fins are even for if you say things like this. Contact with the tubes is irrelevent. The fins radiate the heat.

If contact is irrelevent then the fins are useless. (BTW the fins don't radiate heat, that would make it a "static" or a plain air cooled condenser, not forced air. The fins job is to add more surface area to allow more heat exchange then a bare coil alone would allow. So I know very well wherefore i speak.

My statement said that the water would take the least line of resistance and flow down face of the fins and do no useful cooling.


Uh, ya, sure, whatever you say. Water is a much more efficient means of thermal transfer than air. Evaporation is not needed here.

Water would be a more efficient heat transfer medium in the eqipment designed for it.
And you missed the point on evaporation completely. I said (even if you didn't get the point) that the fowing water would not have any beneficial effect on condensing the liquid refrigerant because the evaporative effect that MIGHT have occured would not be able to manifest it self because the RH is 100% as it was raining.This disallows the air from absorbing the water and kills any evaporative cooling.

I refer you to "Evaporative Condensers" if you need more guidence.



cracking the bi-metal of the motor???? I can understand if you said, the bimetal thermal strip of the Klixon switch cracked and thereby causing intermittant and undependable operation but you said the metal of the motor cracked. I think you arecracked.


Following is what I actually wrote..

Klixons were famous for cracking the bi-metal of the motor they protected
and would operate intermittently.

this the lie you wrote:

cracking the bi-metal of the motor???? I can understand if you said, the bimetal thermal strip of the Klixon switch cracked and thereby causing intermittant and undependable operation but you said the metal of the motor cracked. I think you arecracked.


I think i have proved my point. You obviously lack a full set of skills so you like to blow smoke.
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Old 06-14-2009, 06:46 PM   #28
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AC stops cooling when it rains


Thanks Nap and others. I have been in this biz a LONG time but definitely have not seen it all. Don't seem to have too many hard start conditions where I am but I have heard that is a problem with some TX valves and scroll compressors. Most manufacturers have accessory hard start kits with potential relays for that issue. Only internal overload trips I have had where from heat, but amperage creates heat. Always seems to lock the rotor and trip the circuit breaker IF it is properly sized, some are not. Good to share info with others.
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Old 06-14-2009, 06:47 PM   #29
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AC stops cooling when it rains


Quote:
Originally Posted by yuri View Post
Skip, FYI and others the overload is a heat only activated device and trips when the unit is run out of freon and grossly overheated. Overload/overcurrent protection is done by the cicruit breaker. Slugging will wreck the valves and it won't ever pump properly again. Just trying to be educational. OP needs to by a amprobe clamp around the wire meter and check the amps when he thinks it is not cooling and let us know if the compressor is drawing amps. The cond fan motor draws very little. Just finished the mystery of the backwards running cond fan motor and now we have this one. Interesting.
Yuri

Thanks for that. I stand corrected.I was thinking of a fractional hp refrig comps that are amperage and heat sensitive.
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Old 06-14-2009, 06:50 PM   #30
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AC stops cooling when it rains


Usually it trips the circuit breaker as they heat up VERY fast/designed to trip VERY fast and the overload takes longer, but it could go first if the breaker or fuse is too big. Have not seen a backwards running cond fan but now I know what to look for if it happens. A blob of silfoss from a poor welder can do wonders to a RFC control when it floats around. Now that was a strange intermittent problem. Eventually blew the compressor from excessive relief valve popping.


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