A/C guru challenge for over heating fan

[shottys]

I replaced the old fan for the condensor because it over heated and started making loud noises. New fan is installed along with a new capacitor for it, that is rated for the fan. Now the fan is wired for 230V with a cap, 4 wire. I know the fan is wired right. now if i disconnect the compressor motor the fan will run for ever and not over heat. if i connect the fan and run the compressor at the same time the fan will over heat with in a few minutes. I did not rewire anything all wireing is the way it was before. typical system; fan, cap for fan, condensor, compressor, cap for compressor. Home unit 2 story house

[Grady]

Have you checked fan rotation? Turning the wrong way can cause this. Also try wiring the fan wires directly to the lugs on the contactor. Check amp draw & voltage on the fan motor wires with & without the compressor running. The compressor could be pulling power away from the fan. If this is the case, I suggest changing the contactor. This could be interesting. Please post back in the same thread with results.

[shottys]

Have you checked fan rotation? Turning the wrong way can cause this. Also try wiring the fan wires directly to the lugs on the contactor. Check amp draw & voltage on the fan motor wires with & without the compressor running. The compressor could be pulling power away from the fan. If this is the case, I suggest changing the contactor. This could be interesting. Please post back in the same thread with results.

The fan is rotating (when looking from behind the motor it is going counter clockwise. The air gets pulled from the outside in past the fan then over the condensor, is that the correct air flow direction

I don't have air conditioning down to a science but I am fairly familiar with it, and i am awesome with electrical stuff. I have 2 theories for this but am looking for another person with experience with these devices and you did hit one of my theories in your response. Not the air flow thing

[shottys]

The voltage when running did show about 5 volts lower with the compressor motor running.

By contactor do you mean relay box

[KField]

It sounds like you may have the rotation reversed. The air should enter the condensor from the outside and exit up through the fan blade.

Ken

[Grady]

Five volts is not significant. As Ken said, it sounds like the fan is turning the wrong way.

[shottys]

thanks guys i really appreciate, i am going to try switching the direction now, the new fan has some wires i can change to do that.

Also this unit is a rectangular box and the air only passes from one side to the other if that matters.

I don't understand why flow direction would do that could some one explain this, i can't change the direction till tomorrow because it is dark out and i have no flash light here

Another thing the fan has a high and low setting which should i use. The manual for the motor doesn't state what the rpm is for either

My other theory was that the capacitor for the compressor was going bad and excessive harmonics were entering the line causing the stator of the fan motor to be over saturated and over heat

[Grady]

If this unit discharges horizontally, the air should be drawn thru the coils & past the fan. If it blows vertically & the fan under the coils, the air should pass over the fan first & be blown thru the coils.
Often the fan hub creates a dead spot where little air passes over the motor if the fan is turning backward.
What was the RPM rating of the old motor? Common ratings are 825 (or 850) & 1075 (or 1050). Then there are the odd ball 1140,1550,1625, & 1725's.

[shottys]

i brought the old one with me to the A/C store, and said i need one of these, it was the manager that picked out the one to replace it with.

Also it is horizontal discharge so the fan is blowing backwards. if changing the direction works i will post it tomorrow night. Thanks again you just schooled an electrical engineer. I spent hours trying to figure it out

old one is 1075

[shottys]

fan still over heating after change of direction, idea's anyone

Also the relay was replaced about 2 years ago, and that is still nice and shiny

[shottys]

i am probably just going to call a repair man. If i had to place bets, i am going to say i either got a bad fan that was new, or the compressor motor is going bad, And because i am using an analog meter because in this application they are better and will never lie to you like a digital will (which i have had read up to 60V off because of harmonics in the lines). i should use a digital to but don't have that with me to compare readings for the presence of harmonics.

Either way i am done taking this thing apart and putting it back together. I don't have a current meter with clamps so that puts me at a disadvantage. Maybe the capacitor for the compressor is bad. Because it looks like they are trying to simulate 3 phase with 2 phase by using a phase shift with the capacitor.

[KField]

There isn't much besides low voltage or overload that would overheat that motor. If it was too small it will get hot. Did they match horsepower of the old one? Also rpms? If you try to spin that blade faster, you will work the motor harder. Sorry no specific item stands out but you would need to take an amp draw and check it against the motor name plate to get a better idea.

Ken

[shottys]

Same motor rating in hp, i tried it on high and it over heated in the same amount of time. I am waiting for it to cool so i can try it on low, but i doubt that will work to, plus low seems a bit slow to

The new motor is a totaline

P257-e5462

or this number is on the box to 746759

The box says 1075rpm but it doesn't say with what tap. In the one wiring direction included it says to use the high tap

Also the motor has +/- 23V tolerance and I know the motor is operating in that range. According to the analog meter not digital.

[KField]

I can't see how the compressor interacts with the fan motor. It certainly should not. I could see if you shared a capacitor terminal or if one of your fan motor leads was coming off of the compressor capaciotor. But if the 240 volt fan motor leads come off of the contactor and the capacitor leads are just connected to the fan motor capacitor it is a mystery why there would be interaction. Sorry for being no help at all.

Ken

[shottys]

well it just over heated on low setting now.

[shottys]

The devices are wired in parrallel, if the compressor motor is going bad which will cause it to pull more amperage, and lower the voltage 5-10V, this will have a pretty big impact on the fan motor, especially if the motor is throwing off harmonics back in to the power lines, that are feeding into the fan. Harmonics alone can overheat a fan that is operating at normal voltage range.

Ya i can't really explain this for crap but other engineers are fascinated with how i think stuff up, i understand theory but can't explain it. But in a nut shell the a/c compressor is drawing more juice. Won't get into why motors reasons why they draw more juice.

try this if you have 2 things in parrallel and short one out, the other device will fail to, in this case the a/c compressor isn't completely shorted but it is probably the problem. So i am probably just going to replace the whole thing outside, if the ac guy says its the compressor, the one out there is older than me.

[shottys]

did more testing today found out it took 25min for the fan motor to overheat with out the compressor on.

so i paid for a newer broken fan motor at the AC place, and having it wired for high was correct.

So i am just going to replace the whole thing for $2500 after all its 30 years old and don't want to have to deal with break downs again