My house in the Phoenix, AZ area has two gas packs on its flat roof, a 2T and 4T Trane XL1100 unit. The 2 ton often makes a lot of noise when starting. When I finally got around to taking a close look at what was happening, I found that at higher temps it would often stumble upon starting and sometimes start after the internal overload (or whatever else is inside) reset. The cooling performance has always seemed OK.

My first thought was to replace the run capacitor and that seemed to help a little bit. Finally after a long and grueling inspection of every bit of high and low voltage wiring involved as well as the voltage levels and the contactor relay, I concluded that this unit, in this installation, has probably always been hard to start when the temps get high. The unit was manufactured 01/94 and this is the second summer we have lived in the house.

I measured the pressures and compared them to the curves packed with the 2 ton unit and they were very close to the curve for the existing WB temp inside the house over the outdoor temperature range from 70 degrees to 103.

I installed a hard start kit that I removed when I replaced a 4 ton heat pump at our previous house. The GE 3ARR3 K6TV3 relay and 130-16x uf capacitor made the compressor start like a scared rabbit up to the 108 deg high temp for the day.

I know I'm leaving out a lot of details, but I'm confident that there is nothing wrong with the original installation or the few components I mentioned.

Is hard starting a common problem for some equipment in this part of the country? Trane installed kits on some units and not others (according to the data in the units)

Would I be wise to install a starting kit in the other unit also, even though I don't think it has starting problems? At least If there is, it only shows up at temp/voltage extreems and it hasn't caught my attention like the 2 ton unit. Both units get the full late afternoon sun right into the condensor

Would one of electronic units by Supco (or others) be preferable to the mechanical relay and cap? I see Grainger sells some of the Supco line.

Is there any risk in leaving the old hard start relay and cap in the unit? The relay seems to operate OK and there is 280 volts across it when the compressor is running. The cap is in a plastic case that is cracked. It has probably been cracked for years in the old heat pump (vintage 1990).

I don't have much experience with AC equipment, but with 40 years of troubleshooting electrical, electronic and mechanical equipment, and the help of experts like I see here and Google, I can usually learn enough to stop before I get myself into real trouble.

Thanks for your suggestions,