I worked (3 times in fact) for a company who the owner would pay his installers to do habitat homes, donating their time and usually the equipment also. He also never had his company's name on the sign nor did he ever mention it in ads or to customers.
I have been known to do minor stuff for the elderly or disabled.
Replace a compressor or change a coil. I always charge them though, usually 40 or 50 bucks at least. It ain't right to give charity to folks to their face. But cutting them a deal, allowing them to keep their pride, that ain't charity, that's just doing the right thing.
Good for the OP for giving to the needy though.