Why is AC freezing up after replacing fan motor? ?

it's cold outside sometimes

Only are generally only 2 things can cause that condition.

Low air flow across the evaporator coil or low charge.

While most know to keep clean filters in their HVAC system, few ever clean the evaporator coil because it is either difficult to get to or impossible.

Evaporator fins get plugged with dirt over time which restricts the air flow and causes freezing

Well, it sounds like the fan may not be running fast enough. That extra wire may have been for a different speed setting. Like one wire is "low" and the other wire is "high" like on a range hood fan over your stove top. Might have to switch wires and observe the fan speed to see if it increases or decreases. In low humidity conditions, like desert areas, the condenser coils freeze very easily since there's not enough moisture in the air to keep the condenser wet  so the condensation keeps dripping quickly. They use a different contraption in those locations. 

may be because they are suppose to freeze up or you would have a heater instead of a cooler thats why ...

I'm not an expert but depending on the system there should be a sensing bulb that comes from the expansion valve. The sensing bulb may have come off the evaporator, It regulates flow through the expansion valve and helps to prevent freezing.

BTW, I'm kind of wondering if you meant to say evaporator instead of condensor?

WRONG FORUM. You need to ask in the Maintenance & Repairs ·forum in the HOME & GARDEN  category. This is  Cars & Transportation.

Put the CORRECT motor with 3 wires.  Check and check again if you installed the blower the correct way.  Check the charge with a manifold gauge.

I'll wager that the fan is blowing backwards. If it is in front to the condenser it needs to be blowing towards the motor. If the 134a is low in charge it can also ice things up.

I'm gonna guess that the slower motor, even though it doesn't seem to be much, is the reason. You no longer are getting adequate air flow to keep the condenser from icing up. If you can't get a 1100 RPM motor, I'd look for something just a bit faster rather than slower.

Question: Was the horse power rating the same or what?

Various things can cause the AC to freeze up.   One is the lack of air circulating by the fan.  This does not seem to fit your scenario