A/C, low pressure port location

Should I add the oil and the refrigerant to the low pressure valve and does it matter which goes in first

I recently replaced a cracked A/C refrigerant hose on my car, I am pretty sure all the refrigerant leaked out. I know how to recharge the system but I am not sure if I should add oil charge with the refrigerant. Any advice is greatly appreciated. Thank you!

Should I add the oil first? And does it go into the low pressure valve also?

Replaced compressor, condenser, dryer, and expansion valve. System holds 14.5 ounces. Pulled a vacuum, recharged with correct amount, pressures are 30 low side about 160 high side. Liquid line up to condenser is hot but condenser and liquid line to expansion valve remains cool to the touch. Suction line from expansion valve to compressor also room temperature. I am a mechanic for thirty years this one has me stumped. I thought a restriction in the condenser which is why I changed it. This car has the condenser and dryer as one assembly. Temperature at vent is about 80 degrees.

I notice a few days ago that the center vent blows significantly less heat (airflow) than it has in the past. Most has diverted to the outside set of vents on the instrument panel. The upper and lower vents seems to be getting the right amount of airflow if they are selected. It is just the center vent does not seem to be blowing much heat (airflow).

I did notice a sound from under the dash about the same time I notice this airflow problem. It seemed like a sound of a flap snapping shut that would divert the airflow to the center vents properly.

Is there anything that is typical on this vehicle I could check? I am still trying to figure out how to get the climate control system loosened from the dash to take a look inside without tearing everything apart to do it.

Thanks for any help you can give me.

The AC gets cold on the highway (not very cold) but in town it is up and down. It will go cold then hot then cold then hot constantly. Could this be a loose belt? And when I say not very cold I mean not very. Last summer it was very cold. Now it just gets cool.