No cold water coming out of shower head only hot water already replaced the single conector for hot cold selection and replaced the internal cartridge. What next? Thanks in advance

Well you just did what I would have suggested. Now we need to confirm cold water is reaching the mixer. Kill the main, remove the cartridge, close the supply to the water heater and then partially open the main. You should have cold gushing out, if not come back and tell us what happened.

no cold water coming out of shower head only hot water already replaced the single conector for hot cold selection and replaced the internal cartridge. what next? thanks in advance
Close the supply to the water heater and then partially open the main... I don't think I can do this I live in a APARTMENT / CONDO... PURCHASED 2 YEARS AGO I CAN TURN THE MAIN WATER VALVE OFF OUTSIDE BUT THE WATER HEATER / BOILER ROOM HEATS FOR THE ENTIRE 20 UNITS HERE... DOES THIS SEEM RIGHT

Do you have a good flow of cold at all other fixtures? If you are correct then when you kill your main you would still have hot water at your other fixtures. That doesn't sound correct to me. Tell me more.

I have a good flow in bathroom sink and kitchen... not sure how to stop flow the main water heater since it is for all 36 units...

There should be a hot water shut off somewhere inside your home. Otherwise you could not change a faucet without shutting down the whole building. You said you can shut off the cold, the hot shut off should be near by, maybe under the kitchen sink.

When I changed the cartridge and temperature selector I did turn of the water for the whole 32 units.. from the outside main that's all there is here except for the kithchen faucet and bathroom toilet & sink

This is certainly a bad way to plumb a building. I'd shut off all 32 units and install my own hot shut off just inside my unit.