Air Conditioner cycles off after 3 to 5 minutes---need troubleshooting help

I didn't realize I was going to learn so much from this repair task.

I put locked rotor amps in Google and found this response on a forum: (Now I wonder how electric motors in space dissipate heat---like on the Intl. Space Station where I assume electric motors position antennas and solar panels).

Re: locked rotor amps (LRA)

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Just a note on electric motors If a motor is running completely unloaded it will turn at nearly synchronous speed. This speed depends upon the way in which the motor is constructed. A two pole motor running with a supply frequency of 60 hz would in theory turn at 3600 rpm. And a 4 pole motor would run at

1800 rpm. A 50 hz supply would reduce these speeds in proportion to the supply frequency. In these hypothetical conditions the motor would absorb no current from the supply. However as we don=92t yet live in a perfect world, the motor is not 100% efficient. The windings have resistance, the bearings have friction and there are windage losses due to the rotor velocity. These inefficiencies tend to slow the motor slightly. As this happens power is taken from the supply to overcome these losses until the motor speed stabilises at what is termed is =91free running speed=92. As energy is a constant this power is ultimately converted in to heat which in this free running state is dispersed into the atmosphere. For this to happen there must be a temperature difference and therefore the internals of the motor heat up to a temperature at which this heat can be conducted from the motor.

An increasing load applied to the output shaft of the motor results in further slowing of the motor, more current is absorbed to overcome the applied load plus the increased internal inefficiencies of the motor which result in higher internal temperatures. This effect will continue until the load is sufficient to stall the output shaft. The current drawn from the supply at this condition is termed the motor =91Locked rotor amps=92.

However our compressor motors are not designed to operate at this stalled condition. We require them to turn our compressors at a speed to meet with our cooling requirements. Motors are therefore usually designed to operate with a slip of approx. 4 % of full load speed. (Slip is the percentage of synchronous speed the motor is running at). This condition is termed the =91Full load speed=92 and the =91Rated full load power=92 of the motor. The power absorbed at this condition is termed the =91Full load amps or fla=92 This is usually in the region of one sixth of the locked rotor amps. The motor being designed to dissipate the internal heat at this condition without causing damage to the insulation of the motor windings. Allowance being made for short time overload and for starting.

Remember it=92s the temperature limitations of the motor windings that determine the maximum power of the motor. That=92s why we fit klixons and other temperature sensors as the fuses won=92t necessarily protect against overload

So if you switch on a motor direct on line (DOL) it will initially take up to 6 / 7 times the flc of the motor as this is in effect a stalled condition, admittedly normally for only for a very short time.

This starting current in most applications can be reduced by various means depending upon the torque / speed characteristics of the compressor or whatever the motor is connected to.

Some small motors are designed to operate at a stalled condition indefinitely, think of car door window winder motors and some control motors.

Hope this helps

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I don't follow the reference to car window motors. Isn't the power removed at the end of travel?

A little later today I'm going to stop worrying about car windows and the space station.

I will remove the jumper wire I placed on the air conditioner thermostat and reposition the sensor tube. The rubber block appears to be in its proper place, but maybe repositioning will stop the cycling. If it doesn't, I will order the Universal replacement thermostat.

Bob

Reply to
Bob
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Sorry it took so long to get back to you. Sounds like Stormin answered a few of your questions. What I did was go to the item you provided a link for and then put that part number in Google followed by the work specs. A page from another site popped up with the specs. As far as the mounting holes, well in the past when I used universal replacements, at times I had to drill a new hole or 2 in the faceplate to get it to mount. I would rather drill a few holes than spend and extra 70 bucks for an OEM stat.

Hey Big Bob (from Bob);

I love the education I'm getting. Where did you come up with the specs for the Universal type window unit thermostat kit?

SPST= single pole, single throw. What is F.L.A. and L.R.A.?

Is it Universal enough that the mounting holes are going to match, or is that too much to ask?

Stormin Mormon: The tube spacing looks OK, but before I spend buy any new parts, I am going to try moving the tube somewhat and see what happens.

Bob

Reply to
Big Bob

I removed the jumper from the thermostat and repositioned the tube at some distance from the cold coils and fins.

The air condiioner ran about three minutes and cycled off. I guess I've pretty well proven that the thermostat is bad.

I just ordered the universal replacement by phoning the 800 number in the website I mentioned several posts back. They said they'd get it out yet today by UPS ground. I ought to see it by Thursday or Friday. (Is Friday, July 3, a UPS holiday?)

With any luck my next posting on this site will say I didn't have to drill any holes and everything is fixed.

Meanwhile, thanks to everyone here for all the help. Assuming that this fixes the problem, I'm glad I didn't try to get some one to make a service call, or, worse yet, toss my unit in the dump and buy a new one.

Bob

Reply to
Bob

I sense, strongly, that you're going to fix it.

Reply to
Stormin Mormon

"Big Bob" scribblednews:96GdnYOPD_GbFNvXnZ2dnUVZ snipped-for-privacy@giganews.com:

Obviously he doesn't know any of that stuff....so, I myself would chuck the old POS in the trash (SEER 4 maybe?) and go to Conns, Fry's or similar and buy myself a brand new one, with remote controls with SEER rating in the

13s for around $230.

HTH

bill

Reply to
bill

Fixed !!!!

The replacement thermostat arrived after the 4th of July holiday. The holes matched exactly and the part went in easily. So far my air conditioner works just fine. Of course, now it has been unusually cool and I haven't really needed it.

I'm a little late posting this note....and thanking everyone....right after I fixed the air conditioner I had a computer meltdown and was off the air for several days. Today everything at my home is working fine including the computer. I wonder what tomorrow will bring.

Bob

Reply to
Bob

We never doubted you.

"It's always the thermostat" Trademark, used with permission.

Reply to
Stormin Mormon

replying to Bob, Flo wrote: Is the condenser fan turning too slow? if so check the capacitor or the motor may be bad

Reply to
Flo

replying to Flo, SoulSnatcher wrote: Why are you people still suggesting problems and/or fixes? Didn't you see several posts back that it was the thermostat and he already fixed it? Try and keep up huh.

Reply to
SoulSnatcher

Ain't that special. You just revived an old thread to tell other people that they shouldn't keep it going. You are the "you people"

Reply to
trader_4

flashlight through the fins, and I'm pretty sure the coils are plenty clean.

range----ouch!!!!! The Frigidare part # is G158995.

$35 at

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the control circuits are also 220 volts, In the various online parts catalogs I don't see any callouts for voltages for thermostats. Am I missing something here?

I'm having the same problem I did by-passed the thermostat but still doing the same thing

Reply to
OJNATIVIDAD

replying to Bob, BASANT SWAROOP wrote: cooling stop work after 5 minutes & copressor stop workig

Reply to
BASANT SWAROOP

He's been sweating for nine years!

Reply to
Neill Massello

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