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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5483
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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My Trane A/C Condenser fan wont run. The unit is model TTP060E100A0

Customer Question

My Trane A/C Condenser fan won't run. The unit is model TTP060E100A0 and is about 10 years old. Last night the A/C stopped working. I found that the blower and compressor would run, but the condenser fan would not.

I took the top off the condenser and made the following observations:
Fan blades turn freely by hand
No sign of anything blocking them
Resistance on fan motor leads:
brown - purple 41 ohms
brown - black 40 ohms
purple - black 19 ohms

It looks like the compressor and fan share the same contactor, so that seems to rule out a contactor problem.

Resistance across starter capacitor (series with brown motor lead) - open circuit (even on 20MegOhm setting), and even if I repeatedly reverse the polarity of the tester leads.
Removed capacitor and appears that the capacitor plastic case has heated and blistered near the bottom.

My conclusion is the capacitor is probably bad. My questions:
Does this diagnosis sound correct?
How can I be sure that is the only problem, and that the fan motor is OK and there is not some other problem?
Submitted: 3 years ago.
Category: HVAC
Expert:  Phil replied 3 years ago.
Chat Conversation Started
Phil :

Hi, I can answer your question, lets handle them one at a time. Click 'accept' when you are satisfied.. or we can get another expert.

Phil :

The ohm readings on the fan motor you took indicate bad windings in the fan motor, that would be common at age 10 for a fan motor.

Customer :

What resistance should I see there?

Phil :

However your ohm meter reads can be off due to various reasons, there is a chance it is just the capacitor.

Phil :

Common to Run winding will be the low read

Customer :

Which is Common - Run (by color)?

Phil :

Common to the start widing will be the next lowest read, about 30% greater than common to run.

Phil :

and between run and start windings you get the total of the two reads on a good motor

Phil :

Your reads are way off on all counts.

Phil :

I have no way of knowing by the color codes which is run winding etc.. those change like the weather with fan motors.

Phil :

regardless those numbers dont add up, and you did check all 3 combinations..

Phil :

also... very vew fan motors last more than 10 years..

Customer :

So do you suggest doing any additional testing, or just replace fan motor as well as capacitor?

Phil :

Regarding the capacitory... for fan motors those are *run capacitors, metal case, not plastic. Plastic case capacitors are for start only, in 48 years Ive not seen a start capacitor on a fan motor of that type.. you do see them on compressor hard start kits though.

Phil :

leave the compressor wiring alone to be safe.

Phil :

ooops... capacitor I meant

Phil :

Odds are in the 99.9% range the fan motor is bad...

Phil :

If you can find the run capactor for the fan motor I can tell you how to do an 80% reliable check on it... and a 100% reliable check if you have a capacitor checker available.

Customer :

The wiring goes like this. Black wire from fan goes to contactor. Purple and brown wires go to two sides of plastic capacitor (about 3 inches long by 1 1/2" diameter cylinder). A separate red wire connects the side of the capacitor (purple wire side) to the other side of the contactor.

Customer :

There is another much larger capacitor in the unit, but it is wired to the compressor, not the fan.

Phil :

Its wired for a RUN capacitor.. those are in the circuit at all times, and are oil bathed for durability and adequate cooling of its internal components, layers of insulating paper and metal foil... but you have a START capacitor installed insetead..those have no oil or capability to be energized constantly.. those burn out if used as run capacitors.

Phil :

Read me the microfarad rating stamped on the capacitor we can go from there.

Phil :

I cannot be more than 99 percent sure so far, but it sounds like someone has replaced the run capacitor that came with the unit with a start capacitor, probably of the wrong microfarad rating as well.

Phil :

Get back to me with mfd rating, we can go from there.

Phil :

NOTICE; if the capacitor has blisters, it has been overheating.. those have been known to EXPLODE.

Customer :

Here is a picture of the capacitor - looks like it is 7.5 uF

Phil :

That condition also points to a missaplied capacitor.

Customer :

Full Size Image

Phil :

7.5 uF is close enough... that looks line a run capacitor, metal case plastic coated judging by the top seal on it, but i cant be sure.

Phil :

Those can explode as well when they short internally..

Phil :

they can explode when testing them sometimes as well

Customer :

Here is a top view as installed

Full Size Image

Phil :

To do the quickie ohm meter check on that do this

Phil :

Thanks! its a run capacitor, the 7.5 mfd rating confirms it.

Phil :

Do this check and other tests etc at your own risk, from here I have no way to assess all aspects of the situation.

Phil :

disconnect the capacitor, carefully not which wired go to the marked terminal on the capacitor.

Phil :

then using a analog type ohm meter (dial/ needle type) and watching for a slight jerk of the needle when you first touch the leads across the capacitor

Phil :

... see of the needle rises briefly a faint amount before falling back.

Phil :

if it does its generally a good capacitor.

Phil :

if the needle doesnt move.. its probably bad

Phil :

digital meters are not so good for this test, but you can try it.

Customer :

I really don't see a lot of point in testing the capacitor since it is blistered, and reading an open circuit at the megohm level (even on reversing polarity).

Phil :

Regarding the motor again..odds that its windings are bad are in the 99% range, a close examination will show the rotor has been dragging on the stator occasionally.

Customer :

I am more interested in knowing if the motor is OK. I rechecked the resistance on it, making sure that everything was disconnected and get:

Phil :

You are correct re the test of the capacitor.. I just mentioned it because you seemed interested in looking at all aspects.

Customer :

purple/brown - 60 ohms, purple/black 20 ohms, brown/black 40 ohms Does this still sound bad?

Phil :

Ok those are GOOD ohm reads.. the 40 ohm read and the 20 ohm read add up to 60 ohms. in that case the windings would be good. Please note those are different than the original reads which would have been on bad windings.

Phil :

Your meter would also be stable with those reads, odds that it would get a combination that added up by accident are near zero.

Phil :

at 10 years old however, that motor is due to fail... they rarely last longer than that. Look on its end bells for some plugs you can remove to oil the motor bearings, tell me what you see.

Customer :

Took a few minutes to get the motor out. Here are some motor pictures. I am not clear what I am supposed to be looking for:

Phil :

Hello, I dont see the usual oil plugs... but I do see pressed in ball bearings! thats unusual and a very good sign..that motor may last a while longer.

Customer :

This is a Trane remember - they say "It is hard to stop a Trane!"

Phil :

If there is no sideways play in the motor shaft, and the shaft spins freely the bearings are good

Phil :

:)

Customer :

So back to the key question - is there anything else I can do to verify that the motor will be OK?

Phil :

Yes.. buy a new run capacitor and try it... if it runs with the fan blade attached at 1.9 amps its good.

Phil :

You can also do a meggohm test on the windings to ground...

Phil :

some would call that over kill though

Customer :

Would the motor be damaged at all from the line voltage being applied, but not running due to the failed capacitor?

Phil :

It would have over heated.. but since the windings check good on resistance, damage is unlikely.. a megohm test would show any insulation damage.

Customer :

Resistance to case shows about 600K on all 3 leads, but not very stable reading. I can get a similar reading by holding the ohmeter leads in my fingers and checking body resistance (although I was not touching the leads when testing the motor).

Phil :

You are a smart man...

Phil :

600k means there is a slight voltage leak on the windings to ground, but perhaps not enough to cause the motor to fail for some time.

Customer :

OK, Phil - here's the botXXXXX XXXXXne. In Texas, I cannot buy HVAC parts without a license. So I can only order them on the internet. I wanted to avoid buying some parts (such as the capacitor), waiting 5-7 days for it to arrive, only to find I needed additional parts (such as the motor).

Customer :

However, luckily I find that this capacitor is not really an HVAC part - I can buy it locally at a Grainger supply. I will get one Monday, try it, and if it doesn't work I will order a motor. I appreciate your guidance, and you have given me the confidence that this is the right direction to go. You have earned your $18 for all the time you spent with me. Thanks

Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5483
Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial
Phil and 7 other HVAC Specialists are ready to help you
Customer: replied 3 years ago.
Thought you would be interested in this followup. Bought the capacitor yesterday at Grainger supply for $7. Put it in and the system is working fine. Motor runs great.
Thanks again.
Expert:  Phil replied 3 years ago.

Thanks! I do appreciate the follow up.. You saved yourself at least $200, probably more and maybe some misdiagnosis fall out. but then again, you had to spend 7 bucks.

 

You might be interested to know that those things used to cost about that, 7 dollars in the 1970's! The big ones for the compressors used to cost 45 to 60 dollars.. now they are 20 dollars or so... and the dollar has depreciated in value dramatically on top of that.... the US mfgrs buy them for 20% of that... not so bad. But maybe 1 in 10 of those is bad out of the box... still not so bad.

 

***

I used to consult Daikin in Japan, they asked my why virtually all of the US made solenoid coils failed... what! I said they are reliable in the US.. it runs out the they tested them by boiling the coils in salt water for a few days :) Theirs passed that test though.

 

its s strange new world. Thanks again for the accept.

 

Phil

 

 

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