Cold air is coming in from outside, didn't do this before.

the windscreen fog is from humid air coming in from the outside
air conditioners work by removing the humidity from the air so if you close of the outside vent then the recirculated air inside the cabin eventually has all the moisture removed
that is why the windscreen clears because there is no moist air to condense on the cold windscreen
now you will say that it is too cold and that is why you turn it off
well try this -- leave the ac on and adjust the heater control to produce lukewarm air no fogging up and not cold
it is called climate control

is the outside compressor running or just the condensor fan.

The first thing to do would be go to your local auto parts store and buy an air conditioning recharge kit. Provided your vehicle isn't too old, they sell recharge kits that require no tools.

If their is a leak anywhere while you recharge, you will know.

Try recharging the air conditioning first, it is very simple and the kits come with simple instructions.

If there are no leaks, your A\C will blow cold air again. As for the pressure, if it continues to slightly blow air you may be looking at a new air compressor unit or a vaccum line. A new unit will run you anywhere from $200-$2000 dollars plus labor depending on the vehicle.

If the recharge works, at least you will have slightly blowing cold air rather than hot and you can continue that way until the unit fails.

Check the refrigeration lines coming off the outside unit. One should be very cold and one relatively warm. If one is not very cold, then the compressor is not working. Usually you can hear it when it is running. The condenser fan in the outside unit should also be operating. If the compressor and fan are operating, but the refrigeration line is not cold, you probably have a refrigeration leak and have lost the coolant. You will need a service tech for the repair.

Put the vent on inside air circulation,not fresh air,then no air will come out.

You didn't tell the make on your camera, but
I have seen this problem on my own.

I believe it is a dew sensor.

Dew is when a cold device goes outside from the airconditioning, and collects moisture on its insides from the air, like a cold drinking glass. This ia bad thing for that device.

Do not operate it as long as you see that. take it outside in a plasitc bag, and let it warm up first.

If your compressor is running outside (low hum noise) then your probably need freon .If the compressor is not running could be a bad cap or bad compressor

There is a baffle/damper that allows outside fresh air to flow through the unit. This is only supposed to be open in cooling mode when the outside temp is moderate, or whenever you want just fresh air and fan operation.

Find the lever that controlls the baffle.

Some units have a switch in the control panel for this.

Does it look like a box with four flex ducts or pipes coming off of it? if so its a fresh air/ heat recovery ventilator, supposed to bring in fresh air, keep in mind, the outdoor unit does not bring in air, it is just a pump to the indoor unit. that unit may be running independently, or wired incorrectly

Since it is not so hot outside you may have to adjust the Thermostat to a lower setting to get the AC unit to kick on the compressor and blow out cold air. Give it a try, and if not the T-stat then we can go from there.