Fan running backwards

[dnuse]

I have a customer that has a Trane 3 ton condensing unit and the cond fan is running backwards.

I checked the run cap It is OK 7.3 uf so i thought that the fan might be shorted internaly so i replaced the fan motor and run cap put the unit together and it is still running backwards.

the new run cap measures 7.35 uf it is supposed to be 7.5

Do I need to check the Hertz on this system??

Could that be causing the wrong rotation??

HELP PLEASE!!!!

It seems to be moving enough air to condense the refrigerant

any help would be appreciated

[rbartlett]

maybe it's the wrong blade..

cheers

richard

[david.gnaniah]

During the capacitor changeover which must have taken place previously from 7.5 to 7.35 uf they must have have connected the cap in the wrong direction.

Check the circuit once again with the manual. Hopefully this should solve your problem.

[US Iceman]

HI dnuse,

Welcome to the RE forum.

It seems to be moving enough air to condense the refrigerant

Please don't take this wrong, but if the discharge pressure is within the expected range for the air temperature entering the condenser are you sure the motor is running backwards?

If the air flow is not as high as you think it should be, the blade may be on backwards also.

Have you checked the fan motor amps and compared it to the nameplate amperage?

[t-bone]

I had the same problem a few years ago. I can not remember the specifics but the homeowner had purchased the motor themselves and installed it. Somehow they had wired the non-reversible motor to run backwards???? Just compare the diagram on the motor to the one on the unit and you should find the problem.

[old gas bottle]

if its got three or more wires to choose from it should tell you how to reverse the rotation, if its two terminals sounds like its the wrong motor or blade.

[Peter_1]

Because he installed a capacitor, it's definitely 3 wire.
It's mis-wired.
These motors can run in 2 directions.

[wambat]

Because he installed a capacitor, it's definitely 3 wire.
It's mis-wired.
These motors can run in 2 directions.

Peter, It can also be a four wire. If some of you are interested in basic electronic component operation I recommend this web site:
http://ourworld.compuserve.com/homep...ott/index1.htm

[dnuse]

Thanks for the link wambat.

[Peter_1]

Sure Wambat, I better said... a cap needs at least 3 wires.

[Ireland]

Has the motor been repaired, new bearings, etc????

Has the windings section been put back on the wrong way around????

[NoNickName]

This looks like the other thread with the single phase compressor running backwards.

[afeef]

hi all
each single phase motor have 2 starting coil wires and 2 running coil wires .
one running wire is connected to one starting wire .
the other running wire is connected to the other running wire .
if we reverse the connection of the running wires (each wire take the place of the other one) the motor rotation will be reversed
so in your case i think that there is someone who reverse the running wires connections with respect of the starting wires,then the motor revese its direction.
the fan blade have nothing to do with motor rotation direction
thanks&regards

[Peter_1]

the fan blade have nothing to do with motor rotation direction

You have blades which blow CCW and others which blow wit CW running motor shaft.

[herefishy]

Good greif -

Is the existing motor an OEM? Does it have a part number?

Call Trane and find out what is 'supposed' to be in the machine - ask for the part numbers (I recommend changing the fan also) and fit the manufacturer's parts into the unit.

Trane - US ph:903-581-3200 (Tyler, TX)

[NoNickName]

Yes, blades can be pushing or pulling and the motor rotation is accordingly CCW or CW

[US Iceman]

I am surprised this is such a complicated issue. Perhaps some basics are in order here. It can be difficult for new people to look at a fan blade and try to determine which way it is supposed to rotate.

The first assumption that is needed is the fan hub and set screw are installed facing the motor.

The second assumption is that air will almost always be pulled through the coil for refrigeration systems.

Look at one of the blades on the fan. The blade will have a cupped (or concave) area. This is the discharge side of the fan. The leading edge of the fan "cuts" the air in the direction of rotation. The leading edge of the fan is always lower than the trailing edge of the fan.

Set the fan blade on a table top with the hub facing you. One edge of the fan blade touches the table top. This is the leading edge. The trailing edge is the side of the blade that is up in the air.

The air is discharged off of the trailing edge.

See the right hand bottom corner of the page under "Propeller Rotation"
http://www.lauparts.com/catalog/servefile.aspx?id=1995

[Nicolás Vera V.]

I am little confuse.
Perhaps could you confirm if this motor is one phase, or not.

[Electrocoolman]

There seems to be a lot of confusion over this type of motor.
Any motor that uses a RUN capacitor is a TWO PHASE motor and will have two windings.

These will either be brought out separately on 2 pairs of wires (ie 4 wires + Earth) or the windings will be commoned at one point and will be brought out as 3 wires (again + Earth).

Lets look at the 3 WIRE MOTOR 1st:
Quite often the two windings will have a similar resistance value. A simple test with a Continuity / Resistance meter will confirm this and will identify the common wire. The motor capacitor can be wired in series with either of the other wires. The supply is connected between the common and the other wire + other side of capacitor. Changing which wire is in series with the capacitor will change the direction of rotation.

With the 4 WIRE MOTOR:
The two windings might well have different resistances. The higher resistance winding will be the one to connect in series with the capacitor, the lower resistance will be the main winding. The way these two 'windings' * are paralleled will determine the direction of rotation.
*One 'winding' has the series capacitor.
Now consider that each 'winding' has a (S)tart and an (E)nd.
Thus they can either be paralled as S1S2 and E1E2 or alternatively as S1E2 and E1S2. This will determine the direction of rotation.

As others have stated, fan blades are designed for a specific direction of rotation.....when run in reverse the airflow can be reduced by as much as 40%....this is a significant reduction and one must bear this in mind especially with cast fans combined with an external rotor.

Incidentally, it is possible to get a 3phase (star) motor to run on single phase using a capacitor in series with one of the phases.

Hopefully you'll find this helpful,

Regards Adrian.

[monkey spanners]

Work this one out
Prestcold L300 single phase unit. Compressor not running, condenser fan running backwards at about half speed, on for 5 seconds, off for about 20/30 seconds (no contactors etc pulling in with fan operation)
This one had me looking for hidden cameras.

Cheers Jon

[Electrocoolman]

Hi Jon,
sounds like unit miswired....compressor winding gone(hence not running) and cycling on Klixon with fan wired in series with klixon instead of across mains.
Low speed due to half volts on fan but why backwards? What was the answer ?

Adrian

[monkey spanners]

Hi Adrian
This was a few years ago so i have remembered it as best as i can
The control circuit came from the ice bank control/thermostat to the LP swith, HP switch, Klixon, and then to the fan motor live (brown wire). The feed to the contactor coil came from the fan motor capacitor wire (black wire)
The unit had two neutrals, one of which was switched by the contactor and went to the compressor common/neutral connection and the fan neutral.
The other was not switched and i think went to the neutral connection in the units (L300 prestcold) capacitor/relay box.
The contactors coil had failed (no surprise with 300+ volts going to it ) This left the fan with 240v on its live connection, the start winding was connected via its 5uf capacitor to the permanent neutral in the relay box, the fans neutral was connected to the compressors common/neutral connection and so any voltage would have to pass through the compressors run winding, and back out the start winding, which had about 330uf worth of capacitors connected to it (ready to start) to neutral.
So in effect the fan had 330uf on the run winding and 5uf on the start winding.
I think the starting and stopping was down to the compressors capacitors charging up and discharging.

Cheers Jon

[Snowman123]

Is this a Trane voyager unit, they do run three phase fan on two phases with a capacitor on the third wire.

[chillwithit]

are u sure there isnt reversable rotation leads? maybe orange & yellow inclosed in stacons