Bad Capacitor, Bad Fan Motor, or Both?

[Bill R]

Yesterday while running both front and back A/C's, (Front 13.5K Penguin II, Rear 13.5K DuoTherm) both cooling very well, been running for about 2 hours, all of the sudden the front A/C shutdown.  Checked breaker, was good.  Checked power at the unit, have power.  Checked thermostat, all good.  I went on top of the coach to look briefly at the unit, placed my hand on the cover, and it was very hot.  The back A/C cover was just warm.

Today, back on top of the coach, I pulled the front unit cover off, and using my wireless Micro-Aire I turned the fan on low.  Nothing.  But reached in and spun it, it started right up.  Shut it off, won't come on.  Spin, it starts to move again.  Below are other observations and voltage readings.  I am fairly certain that this is either a capacitor or fan motor issue, or both.  

- fan does not start until I spin it 

- fan will stay spinning when going from hi to low speed and the reverse, it only will not start up after I shut the fan off completely

- on low speed the fan seems to run normal

- on high speed the fan makes an oscillating humming noise and is loud

- there does not appear to be any difference in fan speed going from high to low

- inside the coach, air is barely, and I mean barely, coming out of the vents, on low or high

- compressor will kick on, but it is really loud after just a minute, and makes an oscillating vibration noise

- Temperature of the fan motor casing unit was 130F, hot to the touch, the rear unit fan motor only gets up to 108F

- The compressor casing temp was up to 196F, the rear A/C compressor only gets up to 140F

- Capacitor voltage for front A/C fan was 120V on low, and 176V on high speed.  The rear A/C capacitor was 120V low, and 280V high.  What a difference on the high speed.

- the front A/C unit is pulling 4 more amps than the rear with fan speed high and compressor running.

 

I think it is safe to say that the low air flow is causing the front unit to run hot.  Probably shutdown yesterday on high temp.   Bad capacitor causing the fan to run slow, or bad fan motor, or both?  Thank you in advance for any insight.

 

 

 

 

 

 

 

[96 EVO]

Bill, when my front Duo therm 'start' capacitor had a meltdown, it was only when the compressor tried to start. Fan ran fine.

So, I think if you have a capacitor issue, it may be the 'Run' capacitor.

[Tom Cherry]

29 minutes ago, Bill R said:

Yesterday while running both front and back A/C's, (Front 13.5K Penguin II, Rear 13.5K DuoTherm) both cooling very well, been running for about 2 hours, all of the sudden the front A/C shutdown.  Checked breaker, was good.  Checked power at the unit, have power.  Checked thermostat, all good.  I went on top of the coach to look briefly at the unit, placed my hand on the cover, and it was very hot.  The back A/C cover was just warm.

Today, back on top of the coach, I pulled the front unit cover off, and using my wireless Micro-Aire I turned the fan on low.  Nothing.  But reached in and spun it, it started right up.  Shut it off, won't come on.  Spin, it starts to move again.  Below are other observations and voltage readings.  I am fairly certain that this is either a capacitor or fan motor issue, or both.  

- fan does not start until I spin it 

- fan will stay spinning when going from hi to low speed and the reverse, it only will not start up after I shut the fan off completely

- on low speed the fan seems to run normal

- on high speed the fan makes an oscillating humming noise and is loud

- there does not appear to be any difference in fan speed going from high to low

- inside the coach, air is barely, and I mean barely, coming out of the vents, on low or high

- compressor will kick on, but it is really loud after just a minute, and makes an oscillating vibration noise

- Temperature of the fan motor casing unit was 130F, hot to the touch, the rear unit fan motor only gets up to 108F

- The compressor casing temp was up to 196F, the rear A/C compressor only gets up to 140F

- Capacitor voltage for front A/C fan was 120V on low, and 176V on high speed.  The rear A/C capacitor was 120V low, and 280V high.  What a difference on the high speed.

- the front A/C unit is pulling 4 more amps than the rear with fan speed high and compressor running.

 

I think it is safe to say that the low air flow is causing the front unit to run hot.  Probably shutdown yesterday on high temp.   Bad capacitor causing the fan to run slow, or bad fan motor, or both?  Thank you in advance for any insight.

 

 

 

 

 

 

 

YouTube to the Rescue.  Note his meter....I have a similar one as do several here.  GREAT investment...

BTW....there are many on this on Youtube.  This one popped up first.  Pretty straightforward.  Let us know what you do and how it turns out.  There is a $350 or so "fix" for a soft start...might be worth a $20 investment in the standard first....

Good LUCK...

[Bill R]

@96 EVO Hey Ben.  Yeah I am referring to the run capacitor when I was referring to "capacitor".  Feeds both fan and compressor. Thanks.

@Tom CherryThanks Tom for the video.  Seems to be my exact scenario.  My VOM does have capacitance.  So it looks like I know what I will be doing tomorrow.

I'll report back what I find.  I am hoping it is as simple as the run capacitor, and thank your for the quick comments. 

[96 EVO]

Carefull with them suckers, if they are good, they can give you a pretty good zap!

Mine was easy to spot. Rather than cylindrical shape, it was football shape! 

[MyronTruex]

No need to buy a meter with a capacitance checker.

You are already up  there and disconnecting the old one to test,  just put a new one in its place. Substitution is a very good procedure when you have a part that is as easy to swap as this one is. 

I rarely suggest "throwing parts" at any electronic issue but in some cases it is a great way to resolve problems and at least to eliminate any possible doubts. It is not uncommon to have more than one problem in a device. Replacing a part can help prevent call backs and is cheaper than labor in most cases. 

For example, our "bird" circuits often use large solenoids that can have burned or contaminated contacts. They might work fine one day and not the next. So replacing it as a preventative measure when diagnosing an issue that seems to be intermittent is a good move. 

[Ivan K]

When that happened to us on the road, I swapped the suspect cap between units to make the more important one to work and had a new capacitor delivered to Amazon box on the way. A little more work but no waiting when in a pinch. I carry spares since then.

[jacwjames]

1 hour ago, Ivan K said:

When that happened to us on the road, I swapped the suspect cap between units to make the more important one to work and had a new capacitor delivered to Amazon box on the way. A little more work but no waiting when in a pinch. I carry spares since then.

I'd follow Ivan's lead.  Quick test to determine if it is the capacitors.

[Bill R]

@96 EVO, @Tom Cherry, @myrontruex, @Ivan K, and @jacwjames.  You all nailed it, but I can't pick all of your comments as the solution.  

I did the quick capacitance test today and the run capacitor was shot.  Both the fan and compressor were 0 uF.

Made a run to the local appliance U-Fix-It shop and got a new and a spare run capacitor.  $46 total.  Installed and now she is running and quieter than ever.  Even seems to blow more air than before.

So I have a couple of questions about these run capacitors.

1) Do the run capacitors just die at once, or is there a slow degradation that will slow performance of the unit over time?  If it is a slow degradation then a quick capacitance test every so often during PM might head off a problem.

2) Both my units are 13.5K BTU Penguin II Heat Pump.   The rear one is older than the front that had the problem.  When I looked at the rear unit run capacitor the spec on the label was 20 + 10uF.  But the one I had to replace had a spec of 40 + 15uF.  Why such a large difference?  Both units look nearly exactly the same except the older unit compressor is horizontal and the new one up front is vertical.  Does it really matter about how much difference there is?  If I had done a swap test would the 20 + 10uF capacitor have been able to run the front one?

Thank you for helping me not only fix the issue, but learn more in the process.

[Tom Cherry]

40 minutes ago, Bill R said:

@96 EVO, @Tom Cherry, @myrontruex, @Ivan K, and @jacwjames.  You all nailed it, but I can't pick all of your comments as the solution.  

I did the quick capacitance test today and the run capacitor was shot.  Both the fan and compressor were 0 uF.

Made a run to the local appliance U-Fix-It shop and got a new and a spare run capacitor.  $46 total.  Installed and now she is running and quieter than ever.  Even seems to blow more air than before.

So I have a couple of questions about these run capacitors.

1) Do the run capacitors just die at once, or is there a slow degradation that will slow performance of the unit over time?  If it is a slow degradation then a quick capacitance test every so often during PM might head off a problem.

2) Both my units are 13.5K BTU Penguin II Heat Pump.   The rear one is older than the front that had the problem.  When I looked at the rear unit run capacitor the spec on the label was 20 + 10uF.  But the one I had to replace had a spec of 40 + 15uF.  Why such a large difference?  Both units look nearly exactly the same except the older unit compressor is horizontal and the new one up front is vertical.  Does it really matter about how much difference there is?  If I had done a swap test would the 20 + 10uF capacitor have been able to run the front one?

Thank you for helping me not only fix the issue, but learn more in the process.

My thoughts.  The design engineers had a reason, probably the starting or peak amps.  I can read, off my remote on my surge protector, amps per line.  BUT, I have both 15 KW.  I’d buy a spare, 20 + 10 UF for it.  BUT the Dometic is over $100 and the Coleman is $75.  WHY?.?  Keep reading.  Your front one will eventually die.  I don’t think replacing the capacitor will prolong it’s life.  The variable startup or soft start will let you get a few more (days, months, years, eons?) out of the front one.  We had a discussion about this a while back.  Putting in an expensive Soft Start, either brand, will NOT increase the life of a NEW unit….so money wasted.  Eventually….the front is gonna die.  Spend $350 or so….gets you X% more life. If the rear fails, you can push it.  But $700 or more is not a good investment for something that will eventually die.  Corollary.  Medicare will not pay for Viagra and a face lift for me.  Not cost or functionally (financially) viable.  But, they will pop for a replacement joint or a new pacemaker as that adds to my productive life….and I can help folks here.  BUT, when I go to that big RV Caravan in the sky….you can’t buy an equivalent replacement.  If that makes sense….I got a piece of FL real estate that is dry about twice a day…. LOL.

Buy a replacment of the same size for the rear….there is a generic on Amazon if you put in AC Capacitor 20/10 UF for $18.  So maybe the 13.5 kW is scarce…IF you have to have AC and Amazon or a local shop doesn’t have one and the local shops don’t carry that odd size….maybe the cheap spare makes sense.  A highly recommended 40/15 UF is only $18 on Amazon….I’d buy the cheap Amazon, if there are no other name brands a ittle higher……and keep it.  The front AC gets more use. You’re good to go there….That’s my take…..

You’ve about convinced me to purchase a spare capacitor for my two.  All the AC techs for home AC carry capacitors.  They go or a stray lightning bolt or some freak oddity onnthe grid takes them out.  $150 service call to keep a $8,000 system running.  Good investment.  $350 for a way past its normal useful life AC….not for me….but many folks extend the life of their systems.  Who knows….They may sell them?

That’s my logic.

YOU DONE GOOD….thats the main thing….

 

[Ivan K]

Capacitor sizes are calculated based on motor size and winding design. Obviously, the design has changed between your rear and front compressors. I doubt Dometic makes the compressors. Run capacitor size effects performance and could cause overheating of the windings so run capacitors have pretty small tolerances compared to start capacitors which are in the circuit for a short period, to give it the initial kick. Easystart has little to do with running the units, its value is in lowering starting current through the start winding of the compressor by learning how to ramp it up as necessary instead of an instant inrush that a simple capacitor would provide for just a short duration. It completelly eliminates OEM start capacitor. This way, the unit can run off a smaller generator, for instance. In my case, two units on 30A shore if necessary. If your problem was with hard starting but then running fine, like sometimes with an old worn out compressor, a cheap hardstart unit for $20 or so could keep it going for some more time. Those cheap hardstart units effectively double or even more increase the size of a starting capacitor . Opposite to what Easystart does. These relatively large size capacitors are nothing but 2 or more long strips of rolled up metallic foil with insulation that can eventually burn at any part inside the roll and change or lose it value.

[96 EVO]

My front unit start capacitor blew about 5 years ago. Replaced it with an Amazon (probably made in China) unit. Same spec's as the original, and the heat pump is running good as new!

Will the unit die one day, you bet it will! They ALL will!

But just not today !

[Bill R]

3 hours ago, Tom Cherry said:

My thoughts.  The design engineers had a reason,

2 hours ago, Ivan K said:

Capacitor sizes are calculated based on motor size and winding design.

To the point about design specs, and being an engineer myself, I decided to dig further on the compressor for the front unit that I just replaced the run capacitor for.  It is an LG GJS134C rotary fixed speed compressor.  I was able to download the specification sheet and it states that the run capacitor should be 55 uF.  WHAT?  What was there was 40 uF.  Now I am beginning to wonder if this was not a factory installed run capacitor and someone just decided to put in whatever closest available capacitor there was.  An unfortunate common thing done by AC techs, not all.

I also know that a too low rated run capacitor can overheat.  Maybe that is what happened here?  And another interesting point is that this LG compressor does not require a start capacitor.  The wiring diagram of the control board actually say optional.  I am going to look to see if there is actually a start capacitor.  I don't recall seeing one now that I think about it.

I looked at the fan motor plate and it does say that the run capacitance is 15 uF.

So it looks like I need to go purchase a 55 + 15 uF run capacitor based on the engineering specs of the compressor and fan motor.

[Ivan K]

That is an interesting find. Mine are 20/10 like your older one but I never looked at the stickers. 

[Georgia Mike]

I replaced mine last year and that’s what I found on my Penguin.

 

[Bill R]

Thanks @Georgia Mike.   My bad run capacitor does not look anything like yours and only 40 + 15 uF.  As I suspect previous repair replaced with what was available and not what is specified.

@Ivan K My older unit is a reciprocating compressor and like yours requires 20 + 10 uF.  The newer front one is a rotary compressor with different specs.  

Lesson learned:  Always look at fan motor and compressor name plate to confirm run capacitance requirement.  What is existing may not  be correct.

[Tom Cherry]

Wonderful discussion.  From a pure engineering standpoint, which is what we had to do when we had similar issues with equipment that was broken, the only “real” way to determine what the proper capacitor should be would be to download the parts breakdown for a specific unit.  Then take the OEM PN & google it.  With all the online photos or ads, the uf values are probably listed or on the ad copy that the vendor downloaded.  Now that assumes that Dometic installed a capacitor that was correct for that model.  

Unfortunately, just saying that this is what is in mine without a model number or size is a bit confusing.  We have MH with two 13.5, one each 15 & 13.5, two 15 (mine)…then the 3 AC, which I always assumed (stupidly) were two 15 & one 13.5.  

BILL R made a good find by referencing the compressor & finding the correct one.  If he is curious, google the Penguin/Dometic PN….MAYBE with the word capacitor and get the OEM Dometic PN & see what that is.

out of curiosity…..my first hit for Dometic RV capacitor chart was this.

https://pantherrvproducts.com/capacitors/

if you click on the individual capacitor, at least one or two that I tried, there is a “compatibility with” listing.  But some of the PN didn’t look like the ones I am familiar with.

I scrolled down some of the other “hits” in my search.  

  this, to me, was a very informative video.  The same process that Bill R used…

I’m gonna, later this morning, pull my build sheet and get the Dometic info for my two, identical 15, and will share it…

[cbr046]

51 minutes ago, Tom Cherry said:

I’m gonna, later this morning, pull my build sheet and get the Dometic info for my two, identical 15, and will share it…

@Tom Cherry which may or may not be correct!  With all the parts substitutions by suppliers you never know what's really in there, build sheet or not. 

I do like @Bill R's approach - when in doubt look at the compressor and fan plates. 

My HVAC Tech buddy sold me a $35 capacitor for the house when I could have gotten it on Amazon for half that.  He said all capacitors are NOT the same build quality and there's some real junk out there.  We camped together, raced together, ate together . . . .  and he's done lots of work for free so I know he wasn't jiving me.  His capacitor had a lifetime guarantee (mostly I find those guarantees to be more trouble than worth), so maybe partly the increase in price. 

Most big company techs thrive on selling $20 capacitors for $100, and that's on top of showing up and labor fees.  Part of their "compensation plan". 

A capacitor will frequently swell as it's dying, another tell-tale sign. 

In capacitors size *IS* everything!  No fun mounting a capacitor in a clamp that's not the right size. 

A capacitor stores energy, which is why, after all power is removed, you short the lead to ground (pliers, screwdriver, NOT your finger!) as a safety precaution. 

A capacitor offsets the motor's winding inductance and effectively changes when the current flows by a few degrees (voltage vs current).  Once the motor starts spinning the magnetic effects take over inhibiting the current to a much lower value.    Who remembers their righty-lefty electromagnetic vs current theory?  They taught us both ways:  Right thumb points direction of current while the fingers point the direction of magnetic field . . . . or is it the left thumb . . . . or is it electron flow vs current flow?  They taught us both ways and could never remember the difference. 

So there we have it . . . . Maybe why I got a 'C' in Motors class . . . . in 1973! 

I guess André-Marie Ampère was right handed . . . . or was he left handed so he could visualize current vs magnetics while taking notes with his left hand?  So many unanswered questions in life . . .

- bob

[Tom Cherry]

@cbr046

you said..

@Tom Cherry which may or may not be correct!  With all the parts substitutions by suppliers you never know what's really in there, build sheet or not

I totally agree.  But if you go to the OEM documents and then get the correct PN and reference it….then I’d say that the odds of getting a direct replacement will be fairly high.  I am no expert but again, MY buddy, who took several HVAC classes locally at the tech school to work on his family, friends and rental properties, who sold his electrical supply business and was bored at 45 as he didn’t need to work and also graduated MagnanCum whatever in EE from Pittsburgh,  carried a variety in his HVAC tool bag.  He bought them locally from a nationally franchised distributor, who won’t sell to the general public, unless you sing a sad tale… sold the same brands on Amazon.  So…..who knows.

The ones with a 5 star rating and 2000 sold in the last month is not a bad recommendation.  Whether you pay $46 or $18, probably BOTH will last, based on the age of the units.  I had not planned on even fixing one of mine….just putting in both new.  But, for $25….I’ll do a little tinkering….

Yes…I do remember a LOT of those two years I was an EE Student….and then when they told us that half of one course that was driving me bonkers was for my graduate school “preparation”, I and several others marched out of class and selected different Engineering fields….and I made the Dean’s list from there on.  But, I DID learn a lot about DC circuits and it is helpful today….but I constantly learn some basics over again…

Thanks….

[russ2528]

All HVAC compressors (unless they are 3 phase which are commercial compressors)under 5 tons are PSC (Permanent Split Capacitor) style (unless it’s a variable speed, which I have never seen on unit like that) and only requires a run capacitor to operate. Higher end units will typically also have a start capacitor. The compressor was hot due to the high head pressure caused by the condenser motor not working. If the compressor is real hot and not running, it means the compressors internal overload tripped. They normally reset when they cool down. You can use a wet rag to speed up the cooling, If you have an older compressor it’s winding get worn down which makes it a little harder to start and can cause a breaker to trip or the internal overload. Adding a start capacitor will generally solve that. 
 

The run capacitor should always be what the factory spec is. when a motor or compressor has a bad capacitor it puts stress on the windings sitting there hot and trying to start but can’t. I wouldn’t preemptively replace the fan motor, just be aware of it. 
 

The soft start add on’s will extend the compressor life. The hardest thing a compressor motor experiences is when it tries to start. 
 

Keeping a spare capacitor is not a bad idea. You guys are all very helpful and smart. Many heads are better than one. 
(HVAC tech for 53 years) happily retired for 8 years, owned my own HVAC company for 40 of the 53 years. Loved my trade. 

[fixitguy]

Caps were filled with PCBs and would last for 30 years!!! Course now PCB’s DO cause cancer so now the oil is different and caps only LAST 8 YEARS OR SO.

Most often the top rises up like a loaf of bread!! So a visusal inspect first can tell if defective. They are cheap/ and come in a zillion differetnt sizes..

stamps label in small type on the edge of the top HERM [ compressor]  C ]common] and FAN for fan!! take a picture or write down the color code and location.

easy to change its getting on the roof that is dangerout.. 4 most dangerous tools== chainsaw/ table saw / ladder/HA and I cant rell the last one!

 

Edited July 20, 2023 by Tom Cherry
“ (quotes) were removed from comment based on medical facts.

[Bill R]

So to continue this thread, while checking out the rear unit which has been operating fine, I discovered that the start capacitor was totally blown to pieces.  See pic below.  Yet the unit continues to operate.  Doing some research I have discovered that these devices are start capacitors with a motor starter relay.  These devices I believe basically perform the function of a hard start relay.  It is Dometic P/N 3311883.000.  I was shocked at the price on Amazon.  Nearly $70. 

My question is can I purchase a standard hard start relay like these in this link to replace?

https://www.amazon.com/dp/B0878WV8QR/ref=sspa_dk_detail_2?pd_rd_i=B0878WV8QR&pd_rd_w=2X2WI&content-id=amzn1.sym.386c274b-4bfe-4421-9052-a1a56db557ab&pf_rd_p=386c274b-4bfe-4421-9052-a1a56db557ab&pf_rd_r=NDVP01AV3PJ95G5SVZ1D&pd_rd_wg=rpeyk&pd_rd_r=f69f5c1f-c1fb-45b7-91cc-41fd1294993e&s=automotive&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWxfdGhlbWF0aWM&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUFRTTRERDlON0RPSlImZW5jcnlwdGVkSWQ9QTEwMDc4NTVZMDQzSjc4Q0VDMDEmZW5jcnlwdGVkQWRJZD1BMDAwMDk0NzMyR1g3MEtTNjNMTlMmd2lkZ2V0TmFtZT1zcF9kZXRhaWxfdGhlbWF0aWMmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl&th=1

 

 

Edited July 19, 2023 by Bill R

[96 EVO]

No answer for you Bill, but I'm surprised that compressor will still start!

[cbr046]

Would a Soft-Start bypass that starting cap?

- bob

[russ2528]

When using a soft start system you will remove the start capacitor. The purpose of the soft start is to reduce the starting amperage (lock rotator amps) a start capacitor bangs the compressor on fast to overcome the compressor starting torque.