Why are fridges hard to open once closed?

Cambridge University engineer Lívia Souza lifted the lid on this question from NeilEP from The Naked Scientists forum... 

Lívia - So the idea is the fridge is closed as a container containing cold air inside of it. So you open the door and let's say it's summer outside and all the hot air is going in and the cold air is coming out. And then when you close the door, what happens is this hot air that went in, starts to cool down and then when it happens it decreases the pressure. And then you have a tiny vacuum and takes a while for you to be able to pull it.

Chris - So it's the air that goes in that's warmer and therefore at a higher volume because it's warmer.  Hitting the cold surface inside the fridge and shrinking so the pressure inside the fridge drops. And presumably then if you kept on opening and closing the door as the temperature went up inside the fridge, that effect would go away. And also if you had a fridge that wasn't on it should be much easier to open it.

Lívia- For sure.

Chris -  Is that true? I haven't tested that. That would be the scientific way to approach this. We need to actually do the experiment.

Duncan -  I can confirm that warm fridges can be opened fine. When I moved house there was this bizarre situation, we had multiple fridges and we just used them like cupboards and they were totally easy to open.