What will be the change in room temperature if door of refrigerator kept open?

Ans: NO, Rather, temperature of the room will increase over the time, not instantly.

Why?

To understand this, let us first understand the working of domestic refrigerator. It contains four different equipment namely compressor, condenser, capillary tube and evaporator and it also has refrigerant or working fluid/medium which continuously circulating through all these four different equipment to enable heat transfer and thus cooling. The refrigerant while passing through different parts, changes phase and this enable cooling in domestic refrigerator.

A fridge can be though of as a "heat pump". It takes air inside the fridge and cools it by removing heat from it. This heat has to go somewhere, though, and is usually blown out the back of the fridge by a little fan. (If you feel the back of a fridge on the outside it will usually be warm if the unit is running).

For this reason, when a fridge is running it is really warming up the room a little bit. In fact, since we can’t design a fridge to be perfectly efficient (the 2nd law of thermodynamics guarantees this), some of the electrical energy gets converted to heat, so more heat gets dumped outside the fridge than gets pumped out, so even if you open the fridge door to let the cool air escape the fridge will still be heating the room more than cooling it.