Capacitors for A/C units - Montana Owners Club

Ozz · 05-10-2013, 04:24 AM

Just FYI info on the capacitors needed for our rooftops, I was on a service call yesterday, I had a bad capacitor, the compressor was not coming on.
Many times inexperienced servicemen will condemn a unit, thinking the compressor is bad, when it is just the capacitor. The compressor will be hot, not working because the internal overload is open.
Sometimes I will have to bag the compressor with ice to cool it down and after I install the capacitor it will run for years.
Many times (most times) the top of the capacitor will be bulged out, a clear indication of a bad one.. besides the compressor or fan motor not working

But sometimes they are bad and not bulged (rare)
The split capacitor is really two in one, a fan cap and a compressor cap. There is a common terminal, a fan terminal and a 'Herm' terminal, which is the compressor.
You shouldn't need a hard start kit, or capacitor, because it is a capillary feed, not an expansion valve system, and there is a timer built-in the thermostat, allowing the system to equalize pressures. But in older systems the compressor may be tight, and you could use one. They won't hurt to be installed even in a new system. I will include both of them:
Capacitors for Dometic RTU’s (same with other brands in this size)
Dual capacitors 30 5 mfd 370 volts
Supco SPP6E boost capacitor.

bncinwv · 05-10-2013, 05:34 AM

Thanks Ozz for the validation that if something goes wrong with the AC unit, the only tool that I would employ is a telephone!! Hee Hee!!

Bingo

kdeiss · 05-10-2013, 07:29 AM

[quote]Originally posted by Ozz

Just FYI info on the capacitors needed for our rooftops, I was on a service call yesterday, I had a bad capacitor, the compressor was not coming on.
Many times inexperienced servicemen will condemn a unit, thinking the compressor is bad, when it is just the capacitor. The compressor will be hot, not working because the internal overload is open.
Sometimes I will have to bag the compressor with ice to cool it down and after I install the capacitor it will run for years.
Many times (most times) the top of the capacitor will be bulged out, a clear indication of a bad one.. besides the compressor or fan motor not working

But sometimes they are bad and not bulged (rare)
The split capacitor is really two in one, a fan cap and a compressor cap. There is a common terminal, a fan terminal and a 'Herm' terminal, which is the compressor.
You shouldn't need a hard start kit, or capacitor, because it is a capillary feed, not an expansion valve system, and there is a timer built-in the thermostat, allowing the system to equalize pressures. But in older systems the compressor may be tight, and you could use one. They won't hurt to be installed even in a new system. I will include both of them:
Capacitors for Dometic RTU’s (same with other brands in this size)
Dual capacitors 30 5 mfd 370 volts
Supco SPP6E boost capacitor.

Ozz that is what I am looking for 30.5 370 Now I can head up the roof with Cap in hand. Thank You Ken

Ozz · 05-10-2013, 10:09 AM

You bet Ken, I think you were the one that asked that question when I was wanting often needed parts list and other MOC info.
It is a 30 mfd for the compressor and a 5 for the fan motor 370
I just changed out a 45 5 370 on a 3 ton residential unit.

kdeiss · 05-10-2013, 10:46 AM

Thanks again Ozz I sold Parts,Wire and insulation to motor repair shops for 40 years.
When I get back home to Pittsburgh in a week I will stop by one of my old customers and pick up a 30/5 370 cap

Ozz · 05-10-2013, 01:11 PM

It's good to be connected like that.

snfexpress · 05-16-2013, 01:07 PM

Ozz,

The Supcos we installed allowed our Honda generators at 1 and a half speed to power ONE AC with no draw down problems.

Nice post.

Leaseit · 06-18-2013, 02:09 AM

Now if there was only a service valve on the unit I would be even happier.

Ozz, have you put service valves on these units before. If so I would like you input and maybe the maker and model number.

Randy

Ozz · 06-18-2013, 02:17 AM

Hi Randy,
No I haven't. It would take specialized equipment to work on a RV rooftop unit. The refrigerant is weighed in them, and the charge is critical. If the unit is low, there is a very small leak, as it only holds a very small charge, topping it off is probably not an option. If there is a line break (vibrating line against another, or a surface,) a guy would drill into the lines, high and low pressure, install a tube with a schrader valve in it, run dry nitrogen into the lines, then braze the broken line, pull a 600 micron vacuum, then weigh the refrigerant in. If there is a coil leak, it is probably time to replace the unit, as other leaks will appear.
Ozz

jswharton · 06-18-2013, 10:23 AM

OK, while I understand in concept, I would not know what to do!

In Houston and believe it or not it get hot! So last weekend I could tell the LR unit was not performing, so I turned it off and eventually went on the roof, took the cover off and . . . . Like I was 16 working on my first car just started touching stuff. There was a large cylinder ( I'm thinking the compressor?) and it was hot, the was a small cylinder attached ( the capisitor?) any way asked the wife to flip the unit on, the fan started and waited for the compressor to start, hmm nothing, so I started banging some stuff and tapped the box where the wires connect and, I'm back in business, it worked all weeken and cycled on and off, something is screwy. Guidance for a lost sole over his head?

Ozz · 06-18-2013, 10:35 AM

Scott, I think you are doing fine.
Most all newer electronic thermostats... I haven't seen all of them

have a time delay before the compressor kicks on, the fan starts quickly, then after two or so minutes the compressor kicks on.
When a capacitor is bad, either side of the compartmented capacitor, the fan usually hums, and you could start it by flipping the fan blade to rotate, but it would not start next cycle.
The compressor may or may not hum, if that side of the capacitor goes out.
Your unit was probably working fine, as the delay is normal.
(Unless you have problems you didn't mention, or I missed.)

Gkerlin · 06-18-2013, 11:01 AM

Scott, just a thought but perhaps you were simply iced up.

Like Ozz said - there is a delay in the compressor start but the time your unit was turned off might have just been enough to melt the frost.

My LR unit is notorious for icing up if I run the fan on auto on a hot day. As it cycles to low speed I think that's enough to start the problem So - when its hot out I run the LR fan at high instead and it no longer ices up.

jswharton · 06-18-2013, 12:07 PM

I thought of that, but not sure how to know? I had walkways thought it was in / on the fins? Or is it the compressor that freezes? When I got up there there was sweating on the tube exiting the compressor (cold side). On my list to tools to get was an IR thermometer. By touch I would have guessed the cold air coming out the inside vent wasn't cold enough. But I am getting a bit older and insensitive, I mean have lost some sensibility in my hands, whew!

So I got one and shot both intake and exit vents, about 20 degrees difference so all is good!

Thanks for the feedback, you guys are great

You may also like: