On 2/11/2012 7:37 AM, JIMMIE wrote:
On Feb 11, 1:30 am, The Daring
wrote:
On 2/10/2012 5:01 PM, JIMMIE wrote:

The HVAC guy told my wife the motor run capacitor on my AC unit needed
changing because it measured 4 instead of 5. He didn't say 4 or 5
what, I'm assuming uF. Does this really need to be replaced?

Jimmie

A new capacitor that size is not that expensive and from the value of
5uf I have to assume it's the run capacitor for the blower or condenser
fan motor. If the tech tries to charge you more than $20.00 for the cap
which wholesales for $3 to $5, he may be trying to rip you off. The cap
value dropping from 5uf to 4uf is quite a bit and could be an indication
of a capacitor that's failing. I've had to replace a lot of defective
capacitors for customers in the last decade because all the damn things
are coming from China. If you decide to have it replaced, ask the tech
to replace it with a higher voltage rated capacitor. If it rated at 370
volts AC ask the tech to install one rated at 440 volts AC.

TDD

Ive never heard of anyone measuring the things before. While I am not
officially an HVAC tech, I work on radar systems, I wind up doing a
lot of the preventative maintenance on the ones at work and our tech
orders dont call for checking caps for capacitance. What they do call
for is measuring the start and run currents and recording them to
show trends and verifying the right capacitor is being used. If the
current is out of spec the first thing on the trouble chart is change
the cap. Over 25 years Ive changed a lot of them but never because I
measured the capacitance.. I know the environmental techs dont measure
capacitance either, they do check leakage current along with all the
other checks. I also know that even the best multimeters tend not to
be that accurate at measuring capacitance and I doubt like heck he is
carrying a capacitor analyzer around with him. Just didnt sound like a
good reason to fork out $100.

Jimmie

I check the darn things all the time because power surges and near
lightning strikes pop a lot of capacitors in AC systems. For folks
living in rural areas, I've been installing surge arresters on the
furnace and outdoor condensing units because of not only capacitor
damage but newer units have a lot of expensive circuit boards where
the older systems relied on relay logic controls. The more conscientious
HVAC techs use a capacitor tester on a regular basis because more damage
is caused to very expensive motors and compressors when the Chinese caps
go "POP!". Most of the HVAC techs who have a capacitor tester carry
this one or a similar one:

http://preview.tinyurl.com/6p7c8ld

My own test gear tends to be more elaborate thus more expensive since I
also do circuit board repair work on a lot of different things. If you
have electrical/electronic repair experience, you should be able to get
your own 5uf capacitor at any motor rewind/repair shop, HVAC supply
house or W.W. Grainger. I always replace them with the 440 volt rated
capacitors.

TDD