Hard Start Capacitors

[johnredd]

Is there any downside to using a hardstart capacitor? If it makes starting easier and uses less voltage, would it not make sense to put one on all units? There must be some downside...I just dont know what it is.

any info on this is appreciated!

[timebuilder]

I disagree with the idea that "there must be some downside," if the start components are correct for the application.

The fact is that most units used to have these components from the factory, but some bright spark thought they could save money by eliminating them.

I take it your contractor installed a kit, and you are worried?

[philjafo]

I recommend them on all compressors I service, as timebuilder said they used to be a factory installed part but are often left off for cost savings.

[johnredd]

Thanks for the reply. I am studying HVACR online and by book (Refrigeration and Air Condition Technology). I do have one on a system that I service and I was trying to better understand the pros and cons of a hsc

[timebuilder]

Thanks for the reply. I am studying HVACR online and by book (Refrigeration and Air Condition Technology). I do have one on a system that I service and I was trying to better understand the pros and cons of a hsc

Simple answer: properly designed for the equipment: no problem.

[Ac_man]

What's the purpose of the potential relay and how does it work on the hard start kit??and is it also recommended on r410a units with txv's??

[VTP99]

What's the purpose of the potential relay and how does it work on the hard start kit??and is it also recommended on r410a units with txv's??

The potential relay engages and disengages the start capacitor. This is accomplished by electromotive force. On cap tube systems the pressure will typically equalize on off cycle, not much torque is required to start the compressor. With TXV's the pressures do not typically equalize so more torque is required to start the compressor.

[allan38]

double post

[allan38]

The potential relay is used to detect the start of the compressor and cuts the start capacitor out of the circuit once the compressor is running. It does this by detecting the back EMF generated by the compressor, the back EMF powers the potential relay and opens up the circuit. The start kit also has a resistor across the capacitor terminals for a reason I'm not entirely certain of, possibly to prevent pitting of the relay contacts when the compressor shuts down.


Because each compressor has a differing amount of back EMF generated during operation, the potential relay should be matched to the compressor. Many generic start kits use a large ball park match such as 1-3 tons or 3 1/2 to 5 tons. The two wire start kits use a different type of relay or a PTC resistor (Positive Temperature Coefficient) to remove the start capacitor from the circuit.

In my opinion, a start kit should be replaced as a set, a failed potential relay will cook the start capacitor so just replacing the capacitor may result in a call back.

Note: Some technicians have observed the PTC type start kit may not cool off enough in desert heat to reset between calls for cool. This may result in a compressor overheating and the AC going down. Thus the PTC type start kit may not be reliable in high heat conditions.

[allan38]

Scroll type compressors have enough starting torque to start up against a TXV without a start kit.
That being said, the start kit still reduces starting power consumption on scroll compressors just as it does on reciprocating compressors.

The start kit is used on compressors that use single phase power. Compressors that use 3 phase power don't use them. 3 phase systems are used primarily in the commercial world. I have seen a few 3 phase compressors in residential systems that had 3 phase power at the home.

[rundawg]

The start kit also has a resistor across the capacitor terminals for a reason I'm not entirely certain of, possibly to prevent pitting of the relay contacts when the compressor shuts down.

The high voltage stored in the start capacitor could discharge across the contacts of the starting relay, thus welding them, and preventing the relay from functioning.

The resistor permits the capacitor charge to bleed down at a much faster rate, preventing arcing and overheating of the relay contacts.

[mofotech]

Would any of you guys then even bother putting a hard start kit on a new install? Maybe it is sold as a extra accessory to customer? I put a kickstart on brother-inlaws 8 yr old unit when we did a tune up few months back. Lol, I hope it increased his compressor life. Lollll

[philjafo]

The company I work for has been putting them on for a long time and I can't say that I see fewer failed compressors with hard starts because failed compressors are fairly infrequent. However I will say that I almost never see a bad run capacitor unless the hard start has also failed.