All 3 roof airs failed simultaneously?

[plyonsMC9]

With the power on I'd first check incoming voltage, neutrals can drive you silly trying to find a loose connection, if the voltage looked normal, then I'd turn the power off and check all of the connections even remaking them. All of the bouncing our buses go through could possibly make for loose or bad connections!  Being in the environment of bussing would be to our advantage to do a yearly preventive maintenance in these areas just for that reason!  Trouble shooting is simple divide and conquer, first go to the source and check, then just keep splitting circuit in half until you find the problem!  Never assume anything in electrical trouble shooting, Phil another thing would be to check the receptacle that feeds your bus or the cord even.  I know this didn't give actual specifics but the idea of how should help.   The most difficult problem in electricity is trying to find a problem that won't show itself, a broken wire, or a component that isn't completely broken, they can humble the most experienced electrician!  Good luck Phil!

Greetings Pat,
I will keep the divide the circuit in half concept in mind as I work through this.  Is there a technique to finding the neutral problems? So far, all my readings show steady voltage.  No matter where I am testing, and what the power source is ( land or generator ) - always 121 - 122 volts. 

Thanks again! Phil

[plyonsMC9]

Phil,

Revert back to my post on how to check the capacitors on the fans..

Keep spinning and oiling those motors ....

Nick-

Will do Nick,  covers will come back off again.  I did get the fans to spin very freely & had them pretty oiled up, but will re-do that process on the malfunctioning A/C units.

Thank you! Phil

[jjrbus]

Phil, I am electrically challenged, once I found the capacitors and starters, I simply switched them from the AC that worked to the dead AC and from the dead AC to the working AC. (they are all the same model right?) Time consuming but eliminates tring to figure out if I am useing ohm meter right, am I on the right scale etc. My next step was to switch the circut boards around.
                                                                                            HTH Jim

[plyonsMC9]

Jim, I am very impressed that you figured all that out.  Nice work for one of us electrically challenged.     

Kind Regards, Phil

[oldmansax]

Nick,

Are the fan motors on those rooftops capacitor start? I thought they were just shaded pole motors. I don't remember seeing a capacitor when I cleaned mine last year but, then again, I can't remember where I put the cars keys either! 

I'm just asking. It would be a shame for Phil to further complicate the situation by looking for something that isn't there.

TOM

[Sam 4106]

Hi Phil,
I don't want to offend you, but your posts haven't made it clear, to me anyway, that you have oiled the bearings at BOTH ends of the motor. If you haven't, please do that before spending a lot of time checking for electrical problems. You have proven that the blower motor shafts were stuck so it makes sense to work from there.

Last fall I had the same problem on one of our roof A/C units. The solution was to free the shaft and oil the bearings. If you didn't leave your units turned on long enough to burn something out you should have the same results.
Good luck, Sam 4106

[Nick Badame Refrig/ACC]

Nick,

Are the fan motors on those rooftops capacitor start? I thought they were just shaded pole motors. I don't remember seeing a capacitor when I cleaned mine last year but, then again, I can't remember where I put the cars keys either! 

I'm just asking. It would be a shame for Phil to further complicate the situation by looking for something that isn't there.

TOM

Hi Tom,

Most of the roof units have "run" capacitors on the fan motors not start.

Shaded pole motors are too expensive for Dometic and others to use.....Lol

The caps should be in the control box if they have any.

Nick-

[Sojourner]

About shaded pole (SP) and a permanent split capacitor (PSC):

http://en.allexperts.com/q/Heating-Air-Conditioning-696/Blower-motor-capacitor.htm

Quick starting and use about half the electrical power energy as SP motor is the reason not being use.

About "humming" noise is same as either binding shaft (dry & little rusted) or capacitor is bad or very low electrical power. So do the simple things first at least 110 volts (the lower the voltage, the longer it hums before it spins or never, spins freely and capacitor.

FWIW

Sojourn for Christ, Jerry

PS...I used to rewind motors and moist proof sump-pump motor as well.

[JohnEd]

I was a NCO Work Center Super for many years.  My instruction was that "if you can't get the problem to 'FOLLOW' a component/subassemby when you switch them with a working unit....then you did not prove what went wrong."  Sometimes everything worked after they did the switch,  JJR had the real inside track when he suggested that "a known working part" be substituted in for the suspect part.  If the malfunctioning part starts to work....put the suspected bad part in what was the good system and PROVE it was the culprit by showing that the previously good sys is now bad.  Switching the caps was a real good idea and I would try that with both units and I would make sure that all caps work in you "good" system.

When you turn the bad sys on can you give the fan a spin with your finger?  Not enough torque at start to cut anything off completely.

They keep bringing you back to "oil the shafts" so they must know somthing.  Does the shaft on the good unit spin as freely as the shafts on the bad units?

Good luch here, you are 30% there.  My ac unit, built in 73, still works fine.  Front one was replaced twice that I know of.

John

[Lin]

Just curious.  When you turn on the bad units and you get a hum, did you try spinning the fan by hand to see if it would kick in?  I have had humming motors that would start running with a spin which added to the diagnostic information available.

[Sean]

Most of the roof units have "run" capacitors on the fan motors not start.

Shaded pole motors are too expensive for Dometic and others to use.....Lol

Nick,

I'm not sure I understand this comment -- shaded pole motors are the absolute cheapest single-phase induction motors made.

FWIW, Dometic units are capacitive-start.  They have both run and start capacitors.

A representative wiring diagram can be found in the Dometic user manual.  One can be found on-line here: http://www.dudesrv.com/pdfs/DometicBriskAirUMan.pdf

(Phil, if you don't have the manual already, you might want to download the one linked above.)

HTH,

-Sean

[Nick Badame Refrig/ACC]

Sean,

If read the diagram a little closer you will see that the start capacitor is wired to the compressor and the run capacitor is wired to the fan & Comp..

The combo Run capacitor has 3 terminals, "H" hermetic, "C" common, "F" fan.

Nick-

Oh, Phil said he has Penguins, not Brisk Airs.

[Sean]

If read the diagram a little closer you will see that the start capacitor is wired to the compressor and the run capacitor is wired to the fan & Comp..

Yes, sorry, I was talking about the compressor, which I understand also not to be starting.

In any case, the fan motor is still capacitive-start, just not with the extra start capacitor.  (The "run" capacitor is there to provide differential field for starting.)

Oh, Phil said he has Penguins, not Brisk Airs.

The manual I linked is the Penguin Manual (not sure why its file name is BriskAir, maybe same manual)  -- you  can also find it linked on the Penguin web page here: http://www.dometicusa.com/climate.php?product=50

These should be the correct diagrams for Phil's Penguins with the ADB's.

-Sean

[niles500]

""On - getting the hard starts and wiring them inline with the capacitors - would this be something for a seasoned professional to do, or something I could learn?  I claim total ignorance here.  I don't know what a hard start is or where to find the capacitors!    If I can learn this, I can post pix, to the BBS,etc., for further guidance & questions""

Phil - first off I want to apologize, I replied once to this ? and it must have gone to cyber space - Nick is right if your compressors are working you don't need hard starts - they are like "super" capacitors, if your commpressor is locked down from sitting or wear they will usually get them started.

On the neutral issue - I have seen cases where the neutral is bad upstream and due to how the bond was made the system uses the ground as a neutral (a very poor neutral), small loads can work marginaly this way but when you apply a big load that is when you find out you have a neutral problem - I don't know how you store your bus but it could be as simple as a rodent munching or possibly you used some AL wire?

It is quite possible (not so probable) that all three are just fan motors/shafts seizing but brought to my mind this possibility - If the oiling suggested doesn't work we can always revisit  this. HTH

[plyonsMC9]

Hi Phil,
I don't want to offend you, but your posts haven't made it clear, to me anyway, that you have oiled the bearings at BOTH ends of the motor. If you haven't, please do that before spending a lot of time checking for electrical problems. You have proven that the blower motor shafts were stuck so it makes sense to work from there.

Last fall I had the same problem on one of our roof A/C units. The solution was to free the shaft and oil the bearings. If you didn't leave your units turned on long enough to burn something out you should have the same results.
Good luck, Sam 4106

Offend me Sam?  HaHaHa - I KNOW I don't know what I'm talking about.         I appreciate your taking the time to offer suggestions & your experience.

I have only oiled the bearings at ONE end of the motor.  Didn't even know I could oil both ends.  I'll look to do that.  I do note though that right now the blowers spin quite freely.  Wouldn't the motor have to be very weak right now to not be able to spin the cages that spin freely?

Thanks Sam! Phil