[millertime14693]

My ac was running but not blowing out cold air. i checked the compressor capacitor to find that it was bad. the only one i could find on a sunday was a 35+5. the old capacitor was a 30+3. I installed the new one and it seems to be working just fine. My question is, can I leave this bigger capacitor in the circuit or will it cause too much current over time and eventually burn something up?

 

[HVAC/Stud]

Change it out first chance you get.

 

[lentz]

Change it out to the right size as soon as possible. We do not go over 5% larger. (30-3)?? What is the name and size of your system?

 

[hvacrmedic]

My ac was running but not blowing out cold air. i checked the compressor capacitor to find that it was bad. the only one i could find on a sunday was a 35+5. the old capacitor was a 30+3. I installed the new one and it seems to be working just fine. My question is, can I leave this bigger capacitor in the circuit or will it cause too much current over time and eventually burn something up?

The compressor will run ok, but the condenser fan will be shutting down on the internal line break in the not too distant future.

 

[SkipsAC]

:ditto::ditto:

 

[FrostyBeer]

I think it should be fine, if not why do they say + or - 5 on them?????

It's +/- 5%

 

[udarrell]

You can go +/- 10% of the original MFD Rating.
Problem is that .10% of 30 is 3-MFD not 5; so a 35 it's 2-MFD too high. It takes a 50-MFD capacitor to go +/- 10% up or down 5-MFD.

You could have used a 25-MFD & a 5-MFD wired parallel (line power going to each CAP) in the circuit which provides 30-MFD.
When stocking capacitors all those combinations should be considered.

If the 3-MFD goes to the condenser fan motor; a 5 would be too much, you could only go to a 3.3-MFD.
However, if the 3-MFD is good you could rewire the capacitors so it is left in the circuit to the blower motor.

Single phase electric motors need a capacitor to energize the second phase winding. If the wrong MFD Rated run capacitor is installed, the motor will not have an even magnetic field.

This will cause the rotor to hesitate at those spots that are uneven. The hesitation will cause the motor to become noisy, increase energy consumption, cause performance to drop, and cause the motor to overheat.

FrostyBeer, some actually may say 5%; .05%, as that would be safer than .10%.
Some even say it should be an exact MFD Rating for a Run capacitor; other say 10% for a start capacitor others say 20% for a start capacitor. Keep the MFD Replacement Rating as close as you can to the original!

The Text Book that I go by was 10% Run & 20% Above only Start cap...

 

[jpsmith1cm]

Guys, remember that this is ASK Our Pros and not a DIY forum.

 

[udarrell]

Guys, remember that this is ASK Our Pros and not a DIY forum.

Guess we did a good job confusing him.:grin2:

 

[millertime14693]

Thank you everyone, I appreciate your help. I was not aware of the 5% rule, so I will be going to grainger to get the right size tomorrow. I understand everything you guys are talking about as far as sizing the capacitor, running them in parallel, using the 3microfarad just for the fan, etc. I actually wasnt expecting this much help! Im a union electrician and figured it was too big, but you never know, that's why I asked the pros! Great info. Great forum. I would recommend it to anyone.


PS

I probably wouldve just waited until tomorrow to get the exact size if it were up to me. But the pregnant wife vetoed that idea. I guess they get cranky when its hot.

 

[uzzo2]

I would like to jump in here with an observation. Almost all the capacitors I've been buying off the shelves to stock my truck with over the last couple of years check lower than their rating. I thought they were supposed to check a little higher when brand new. Perfect example is my unit at my home, I put a new compressor in it 2 years ago. Well when I went to service it last year, the compressor was drawing more amps than when I installed it. Not over RLA, but pretty darn close, I did some checking and found out the brand new capacitor I put in it was weak. I had to put another one in it the other day. It's supposed to be a 40, I had to get a 45 off the truck that was only checking 43. I believe it's just junk we're getting from china IMHO.

 

[qwerty hvac]

I would like to jump in here with an observation. Almost all the capacitors I've been buying off the shelves to stock my truck with over the last couple of years check lower than their rating. I thought they were supposed to check a little higher when brand new. Perfect example is my unit at my home, I put a new compressor in it 2 years ago. Well when I went to service it last year, the compressor was drawing more amps than when I installed it. Not over RLA, but pretty darn close, I did some checking and found out the brand new capacitor I put in it was weak. I had to put another one in it the other day. It's supposed to be a 40, I had to get a 45 off the truck that was only checking 43. I believe it's just junk we're getting from china IMHO.

Use AmRad. They are made in the USA.


Sent from my iPad using Tapatalk HD

 

[precision hvac]

Or...
Call a pro.

I thought this wasn't a DIY site?
Waaaay too much info given IMO.

 

[HVAC/Stud]

The +- 10% is the MFD reading limits. It has nothing to do with aplication.
If a motor OEM says 5 MFD there is not +- . You use a 5, nothing else will do.
Show me a compressor motor that says 40 MFD +- 10 %.

You take a capacitor out of the box and check the MFD it is good as long as the reading is +- 10 %.

You are doing a maintance and you check the capacitor, the +- 10% is your limits of the cap, out of the limits change the cap.

I was at the supply house today and a HO needed a cap on a lennox, it was a duel cap, 45/4. The counter guy said no problem here is a 45/5.

I told the HO that was BS. Order the correct one.


STUD

 

[Home&Marine]

Or...
Call a pro.

I thought this wasn't a DIY site?
Waaaay too much info given IMO.

Why call a Pro when you can ask one Here and DIY!