I wrote in about my compressor a while back that was hard to start up when it would try to refill the tank. Seems to be cold natured. Put a lighter weight oil in, might have helped a little, warmed it up with a small heater and it fired right up. I would like to put a Kick Start Compacitor on it to give it that extra boost on these cold days. Has anyone tried this before,will it work, if not why not? If it will, does anyone have any pointers. Don't want to plug up a heater just for that if I don' have to. MY compressor is 2 1/2 hp. 120v.-14amp. On a dedicated 20amp. Circuit. Got to try something, no what I mean.

What is the length of the circuit, and what size wire?

From sub panel 25ft. 10/2wg uf in conduit, 7ft. 12/2wg to outlet. I checked voltage with meter, it's 120. I also checked pressure switch, unloader valve, check valve and all are good.

Since you said you would like to put a capacitor on the motor, not you wanted to increase the size of the capacitor, makes me ask what type of motor do you have. If it is not a capacitor start type I don't think adding a capacitor will work. And if you did add a capacitor, what size would you add?

You said that the motor is a 120 volt motor. Could it be a 120/240 volt motor? If so, rewiring to 240 volts will probably resolve the problem.

39 degrees outside this morning, not that cold in my shop but I had to let the pressure drop to 30 lbs. before compressor would pump(would hum and kick off reset button). Capacitor I want to try is same as on the motor, 130uf 250vac, it's purpose is to put extra power (300% varies) to start up compressor, it's called a hard start kit or a kick start kit to help get a motor started like on cold days, or stuck compressors. The plate reads 120v motor not 120/240v on my compressor. These capacitors are used on AC compressors etc. I think it would work if uf and voltage is the same. Have looked to find if someone has tried this before but no luck. What do you think about this idea. Remember when temps warms up I have no problem.

With that information it sounds like a logical possibility. However, I have another question and I suppose it comes from my lack of knowledge. If the hard start capacitor is the same size, 130uf, as the one you are already using, how can it provide more current to the start windings. Seems to me that it would have to have a higher uf capacity. Could the existing capacitor be weak? It is my understanding that some types do weaken with time. Thirty nine degrees does not seam all that cold for starting a compressor, although my 30 gallon Husky occasionally does the same thing in the winter time. It will occasionally trip the breaker during winter months but it always does it when I'm not around. It stays on all the time and like most air systems, it leaks a little air. It usually kicks on about once a day even though I'm not using any air.

These types of capacitors throw a jolt up to 600% more juice for a good spinning start for stuck or lazy compressors for AC and other appliances. There are several sites on the internet, pull up Hard Start Kit on eBay or supco hard start kit. I'm curious to see if this would fix it in cold weather. 130uf is important from what I read, should keep this number the same as original, the 250vac can be higher. It's only 5 months old, got it on sale but I want it to run when I need it, I also like a challenge. Will probably replace the old one with a regular capacitor first.

As I previously related, my air compressor use to periodically trip the breaker. It hasn't done that recently. It has taken me all this time to remember what I did. I change the breaker. I guess the old breaker had gotten weak. Have you tried a new breaker.

All new panel, breaker, wire and outlet. Did some more research and found out that this compressor has this problem in cold and cool weather and so do many others that is kept in an outside shop without constant heat. I emailed the company before I ordered the Hard Start Capacitor and discussed the problem with a rep. and he said this should fix the problem . If it works it's a cheap fix, $7.60 including shipping & handling.

That's good news.

You stated that you had to let the compressor drop to 30 PSI before it would start. The tank pressure normally is NOT continuously applied to the compressor, it is bled off when it is not running The tank pressure should therefore not affect the start-up. Most (all?) air compressors have a means to "unload" the head pressure from them so it does not start under head/load. Some have a simple check valve, some also have a valve that opens to dump the pressure behind the check valve. You have certainly heard the hiss of air being released when a compressor reaches setppoint pressure and shuts off. Is it possible your unloader is malfunctioning? It sure sounds like it.

Only had the problem when it was cold or really cool in the shop. It's warm now in Georgia and it works great, the weather changed about the time I got the capacitor. I'll save my Kick Start capacitor for next winter and see if it does what they say and what I hope it will do.

Cold will make many problems more apparent, like a weak car battery that starts a car reliably when it is warm but not in the cold of winter. Your compressor may have just enough power to start into the head pressure when warm but not when cold due to the added friction of cold lubricants. This would still be a bad thing and may cause the motor to fail prematurely due to the high startup current and longer start-up times.

I assume it used to start up okay, even in the cold? If it no longer does, something has changed. If you can find out what changed and fix it/change it back then you should be back to normal operation and a longer life for the compressor. You say the unloader is okay, but if it won’t start cold with pressure greater than 30 psi in the tank I suspect the unloader is really not okay. With 30 or 90 psi in the tank, the compressor should start into 0 psi. If you think about it, the tank pressure can’t make a difference if the compressor is unloaded (0 psi at the heads).
If it acts up again there are two ways you can check it out, try one or both of the following. One would be to loosen a fitting to the compressor head or the unloder valve and see if any air escapes. If it does, the unloader isn’t working properly. You could try loosening a fitting when it isn't cold and failing, if the cold is making it not start there may be some pressure at the head all the time, but it only stalls the motor when you add the extra load from cold belts/lubricant. A second way is to note the how it sounds and how fast it gets up to speed with the tank at 0 psi. Then shut the motor off before it hits the set point pressure, say 90 psi or so. Wait a few minutes then turn it back on. If it does not start up the same as it did at 0 psi, there is possibly a load problem related to tank pressure. That points to the unloader and check valves.
An intermittent cap could also cause issues that might make you think it is the tank pressure that contributes to the problem. It might just be the cap happened to work correctly the time you started it at under 30 psi. I don't think that is the problem, but I can't say for sure thatit isn't.

Good Luck!

I bought this compressor new in late September. Had this problem since first cold day, changed oil to 5w20 and could not tell any difference, no belt,all one unit. I will check the unloader the way you suggested, but I have already checked it by your #2 suggestion a number of times when it was cold but no luck. When cold the air pressure had to be 30lbs. Or less, that was necessary. Thanks for the info.