Electrical question - heat pump/airconditioner

warren46 · October 19, 2016, 08:41:42 PM

I got a quote to repair my heat pump. The service tech says the dual capacitor is "weak." The unit runs normally. Repair cost is $329. My question is why should a capacitor, even a "dual capacitor" cost over $300. The dual capacitor is for both the compressor and the fan.

What say the experts here on the Forestry Forum.

Warren

LaneC · October 19, 2016, 10:50:48 PM

I hope this does not sound wrong, but if it is running normally, why is a repair needed?

LeeB · October 19, 2016, 11:19:21 PM

Did he have both hands on your shoulders and blow softly in your ear while telling you this?

Gary_C · October 19, 2016, 11:22:40 PM

A capacitor is in an electrical circuit to resist changes in voltage by storing electrical energy. It is similar to a water storage tank in a piping system. I have no idea how either a capacitor or a water storage tank can get "weak."

In a motor circuit, the most likely cause of problems with capacitors is poor connections that get hot and then fail or complete breakdown of the capacitor itself. If the connectors on the leads are corroded, the connectors can be replaced with new crimp on connectors. The capacitor itself getting weak is not a problem that I would expect.

That being said, most capacitors will cost anywhere from $10 - $50 dollars depending on where you purchase them. If the service man has to order the capacitor, make a trip to your home, open up the unit, install the new capacitor, close up and test the unit, then a $300 cost is not unreasonable. A $300 cost for just the capacitor alone is a bit high.

You might confront the serviceman with a question of how he determined it was weak but you might get more BS.

Brucer · October 20, 2016, 01:26:03 AM

I've heard the term "weak capacitor" used sometimes when an electrolytic (water filled) capacitor had begun to dry out. In theory it shouldn't happen, but it can. The result is a loss of capacitance. Depending what the capacitor is used for, it may cause noisy, uneven operation, or slow starting.

warren46 · October 20, 2016, 05:39:51 AM

Quote from: Brucer on October 20, 2016, 01:26:03 AM
I've heard the term "weak capacitor" used sometimes when an electrolytic (water filled) capacitor had begun to dry out. In theory it shouldn't happen, but it can. The result is a loss of capacitance. Depending what the capacitor is used for, it may cause noisy, uneven operation, or slow starting.

Brucer,

Is there a simple test to determine i a capacitor is losing capacitance?

Warren

Magicman · October 20, 2016, 07:33:26 AM

No, not a simple test. I once had a capacitor bridge that tested and determined the value/capacitance of a capacitor, but that was a specialized instrument. Your technician probably had one and determined the actual values of your capacitor.

I notice that in recent years, the cost of these units have really dropped: LINK

LeeB · October 20, 2016, 07:45:11 AM

Wow, even the fluke isn't too terribly priced and they are always on the high end.

LeeB · October 20, 2016, 07:52:09 AM

Had to look it up. Never knew you could test them.
http://en-us.fluke.com/training/training-library/test-tools/digital-multimeters/how-to-measure-capacitance-with-a-digital-multimeter.html

Magicman · October 20, 2016, 08:04:35 AM

Yup, I had been reading too. My old unit had a bank of known value capacitors and I suspect that a comparison was made with the capacitor being tested. It then applied the high voltage to detect any leakage.

I notice that the new ones apply a voltage and measure the charging interval.

Raider Bill · October 20, 2016, 08:58:13 AM

Around here A/C repairs are one of the biggest ripoffs next to car repairs.

Why was the repairman there? I bet it was a yearly service and he was just padding the call ticket.

If in doubt go buy one yourself and install. Prob cost $50. I bought one last month cost $32.00

pineywoods · October 20, 2016, 09:41:02 AM

A capacitor is one of the simplest electrical devices. Consists of 2 sheets of metal foil with an insulating film (plastic, paper etc) between them. Each sheet is connected to an external terminal..The whole works is just rolled up and encased in some type of container. The "size"is determined by the surface (square area) of the foil and thickness of the insulating film. The voltage rating is the max voltage before the insulating film ruptures and effectively shorts the 2 foil sheets together.
In theory, this type of capacitor is either good or shorted, not much in between. There is another type which uses a chemical film as the insulating medium, the tend to short out with age, but are found mostly in direct current circuits. Most common modes of failure are breakdown of the insulating film and failure of the electrical connection between the foil (aluminum) and the wire lead (copper). It's easy to test a capacitor with an ordinary resistance meter (ohm meter), if anyone is interested I'll detail that in another post

muggs · October 20, 2016, 10:00:36 AM

Do you happen to know if these are start caps [ black plastic] or run caps? [ metal } Muggs

Brucer · October 20, 2016, 03:58:00 PM

Warren -- looks like more knowledgeable folks than me have already answered.

pineywoods -- don't forget the electrolytic type capacitors. They can lose capacitance gradually.

warren46 · October 20, 2016, 07:55:13 PM

Thanks for all of the replies. I think I will pass on the replacement.

Warren

pineywoods · October 20, 2016, 08:29:50 PM

Quote from: Brucer on October 20, 2016, 03:58:00 PM

pineywoods -- don't forget the electrolytic type capacitors. They can lose capacitance gradually.

Yeah, that's the ones with the chemical film for an insulator and they do deteriorate with age. DC only, polarity sensitive.

azmtnman · October 21, 2016, 12:06:11 AM

I made a living doing heating and cooling for nearly 20 years.
A motor capacitor is rated in micro Farads (funny shaped u, capital F). It has something to do with "phasing" on a motor winding with a start and run winding. Industry standards are + or -10% for a run capacitor (which is what yours is.) If it is low, your motors will draw more amperage and could cause them to run hot and kick off on overload and eventually motor failure.
I have no idea what labor rates are in your area but it should take about 30 minutes to change if it's in the most difficult place imaginable. It would be easy for you to change yourself.

POSTON WIDEHEAD · October 21, 2016, 07:39:12 AM

Less than $5.00

jdonovan · October 21, 2016, 03:02:28 PM

you can find the capacitors on the net fairly reasonably priced. Many of the common dual capacitors (start/run) are $30-50 delivered.

I don't understand the markup in some of the trades... I know they guy in the van parked in my driveway costs some money to get him there. I;m willing to pay a reasonable rate for parts and labor, but a < 30 min job to replace a $50 part, really doesn't seem like it should be a $300 bill.

Larry · October 22, 2016, 03:54:35 PM

I rebuild a lot of dead motors and also build balanced rotary phase converters. I use a lot of capacitors and most come from the Surplus Center. All of them are less than $10.

The local motor repair shop is also a source for capacitors. Of course they are higher than the Surplus Center but if I just need one, they end up being cheaper because of shipping costs. They will also test a suspect capacitor for anybody that walks in the door free of charge.

Some years ago I bought a Klein clamp on amp meter from Lowes that also measures most capacitors. It was not that expensive and I use it a lot. A simple analog ohm meter (one with a needle free at Harbor Freight with a coupon) can be used to determine if a capacitor is good or bad but will not tell the actual capacitance.

I should add a lot of bad capacitors show physical signs of being bad. Swelled case, paper or oil secreting from the case, cracked case, and corroded contacts. If one has those symptoms I don't even bother to test it...just replace it.