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memphisflyer · 06-26-2012, 06:42 PM

I have a 2000 Allegro Bay with 2 Duo Therm units on the roof. This weekend my fan quit working in the rear unit. Compressor works fine. I got up there today and discovered that the run capacitor for the blower was actually melted and ruptured. I have spent the afternoon trying to find that capacitor with no luck. PPL is sending me a similar capacitor but not exactly the same. The original is rated at 20/10 and the closest one they had for a Duo Therm replacement is rated as 30/15. So my question is can I use this "not quite right" one or am I asking for trouble. Electronics is my weak suit and I don't want to do anything that is not totally safe. Thanks for any help you can provide.

Pigman1 · 06-26-2012, 07:04 PM

Have you checked Grainger? When I had capacitor problems on our Bus a/c, I was able to get what I needed from them. The Tucson store had what I needed in stock, so we didn't even have to wait.

EngineerMike · 06-26-2012, 07:09 PM

Memphis- not sure of the ratings you mention, they don't look like actual specs but perhaps are some mfgr's model#'s? Capacitors are rated in micro-farads, sometimes with an abbreviation that looks like µf, and in volts. Basically there are two plates in these types of capacitors, one charges positive and the other negative, usually wound in a spiral with a non-conductive insulator layer in between. The insulator usually breaks down & creating a voltage leak (they get hot & maybe "melt"). the voltage rating tells you how heavy duty the capacitor is at resisting insulator breakdown; 120V is the lowest for this type cap, then 240V, then 330, then 440, etc. The micro-farad rating tells you how much charge it will hold.

You need a

run-capacitor

that is in the neighborhood of the microfarad rating you are replacing, and voltage at least as high (but higher is better). The OEM units in my A/C's are something like 45µf and 120V. I'm replacing them w/45µf-330V units for better longevity.
BTW, you can google "run capacitor" and get plenty of hits for selling you replacements.

memphisflyer · 06-26-2012, 08:01 PM

I looked at lots of run capacitors from several different suppliers and no one seems to have the exact one. Here is everything that's printed on the side of the one that the case melted on ( I know some of the information is not needed but in the interest of being thorough, here's all of it):

"Cambridge Capacitors
20+10 uf +/- 10% -40/70C
usFile No E128031
C22.2 No 190
Non PCB 1 Phase
M30G44 4899
Type NY1PG 20+10
Fabrique EN GB.Uk Made"

Thanks again for the help.

sundancer87 · 06-26-2012, 10:04 PM

I wonder if the front A/C unit has the same markings as on the dead cap. It would be nice if it had the standard markings on it, then your problem would be solved.

You know the running voltage of the fan is 110 volts so the operating voltage of the cap will need to be more than that, say, 150-200 volts. The higher voltage rating will be fine as was stated earlier.

If the capacitance rating of the replacement is too small the fan may run slower than normal, too large and it may run faster. However, the markings you have don't help much and I don't know an easy way to figure the capacitance other than an RC time circuit which I doubt you want to tackle.

RV Wizard · 06-27-2012, 02:45 AM

You need a dual 20 uf and 10 uf combined capacitor. I would use any voltage raded capacitor you can find as all will be sufficient but a higher rater one as stated before is better. Do not use the 30/15 capacitor as it will cause the motors to draw a higher amperage and run hot; eventually damaging the windings. The motors are designed to use certain size capacitor to operate at the intended rpm, voltage and load. Capacitors cause the current to lag behind the voltage as seen on an oscilloscope. Using the wrong size does not allow the motor to operate as per design. It may run, and run for a long period of time, but you want to do it right for the life of the motor.

lonestarace · 06-27-2012, 07:23 AM

Quote:

Originally Posted by memphisflyer

Thanks for any help you can provide.

You might go to a MH shop and scronge one out of a old unit?

87Rockwood · 06-27-2012, 07:29 AM

Do you have any ac motor rebuilders in your area? They would have the parts as well.

memphisflyer · 06-29-2012, 04:19 PM

I talked to several parts folks and a couple of A/C experts and that capacitor I need is extinct. However, all agreed that I could use one 20 and one 10 with a jumper between the commons. Works great. Thanks for all your input. As someone new to the motorhome world I'd be lost without this forum.