I have single handle Meon faucet in bathroom. I was not getting cold water in shower, so replace new Meon 1222 (bought from Home Depot). Now problem is water is driping from shower head. How to fix it?

Do you mean you replaced the entire mixng valve or you replaced the cartridge only? Did you graese the cartridge with plumbers silicone grease before installing? If not then try it before doing anymore work.

I replace only 1222 cartridge only. I apply silicone grease on black rubber part.

It sounds that you have some dirt inside the faucet, shut the water to the shower, remove the cartridge now turn on the water for a few seconds to flush out the debris, clean the cartridge and install, hope it is fixed now, good luck.

John

I think John is correct, a bit of debris on the seal. Here is what you can do, return that one to HD and get your money back. Get a free replacement from Moen via their lifettime warranty Warranty Information for Moen Faucets