What Causes My Window Unit Air Conditioner To Freeze Up, With Ice All Over The Coils When In Use Over Night.?

There are two common reasons for a window unit air conditioner to freeze up. Either It needs a good clean or the thermostat is too low. However, it always best to consult a qualified refrigeration engineer as soon as possible if you think there is a problem with the unit so that the problem doesn’t get any worse.
It is always a good idea to turn your air conditioning unit down at night to save energy, but also to help maintain the unit. The unit should also be serviced regularly by a trained refrigeration engineer.
Restricted airflow and a dirty unit could be contributing to the problem. Most units will have an air filter under the front indoor plastic cover and grill, these can be removed, cleaned and replaced easily. The rest of the unit can be cleaned with a toothbrush, but it is important to be extremely careful and gentle. If you are in any doubt or you do not feel comfortable doing so, call a refrigeration engineer.
The most common reason for overnight freezing is having the thermostat set too low. If it is a digital unit set the thermostat no lower than 22 degrees C. If it is an analogue unit it should be about two notches below maximum, note that you should hear your box a/c cycle on and off as it reaches its desired temperature, if it is not then you have it set too low drop the temp until you hear the compressor turn off .The fan will continue to run.
If the problem persists then you should get a professional refrigeration engineer to have a look at it.

You have to recharge the system, its most likely low on Freon. You may also have the temp set to low and the air conditioner can't cool the area your trying to cool .It may be to small of a unit .Most people try to use an air conditioner to cool to large of an area .Then when the room doesn't cool to what you want you turn the setting lower . This doesn't help, all it does is overwork the unit and they freeze up .

Also you need to clean the coil fins. They get loaded with dust and dirt. Use a toothbrush to clean them. (Don't bend the fine; this will restrict the air flow.) Also make sure that the air vent is closed, your not trying to cool the air coming from the outside, you want to cool the inside air. You use to be able to charge the units yourself, but nowadays you need to get someone in to do this. (Go. Rags.) This should help with your problem

It needs to be cleaned as soon as the ice begins to thaw you will see the gook use a tooth brush and gently carefully ... Piece by piece wipe & pull the dirt out careful not to bend the fine thin fins... And wash and rinse the brush each time its not  as tedious as it sounds.. Also the window unit must be tilted back enough that the water drips out of the back of the unit .. I have a dry mode..which dehumidifies.. (love it) I I place a bucket underneath to catch the drip so bugs are not drawn.. I used to have a hose/tubing attached to the drip spout and it was long I let it drip into my flower bed but have since removed the flower bed from  the yard. The hose must be going in a down slope. Also I cover the unit during the winter(the outer part of it) one year I did not and had to carefully blast the back of it with a thin stream of water to get the dirt out.. Too lazy to remove it completely to do it right. Thats what you are supposed to do.

You may want to try turning the a/c down at night. If it is on high cool all night it may do this. But restricted air flow can surely be the problem. Most units do have a filter under the front indoor plastic cover or grill. It is usually just a sponge type of material and can be washed and dryed and reinstalled with ease.

If the problem persists you should have an a/c professional look at it. If you have not had it serviced in some time (or never) you should do so. Most of the time the problem can be fixed and your a/c will last a long time.

I am a refrigeration/air conditioning mechanic and it could be a couple of reasons the most common is having the thermostat set two low if its digital st it no lower than 22 degrees if analogue about two notches below maximum note that you should hear your box a/c cycle on and off as it reaches its desired temperature if it is not then you have it set two low drop the temp until you hear the compressor turn off .The fan will continue two run
(some split type a/c's will not cycle off)

Can you get a hose and spray clean the a/c unit or what type of cleaner should you use to clean the vents

Forget that ,, a technician never can fix an air conditioner NEVER . They just tell you it is cheaper and better for you to just buy a new unit. ( never fix ) I am 57 y/o and have been dealing with these problems for 40 years ,, a technician never fixes any ac problems , ever .

If it get's cold at night time your A/C will freeze up just shut it off at night you should not need it if you keep your windows closed good luck mine does the same thing

You can check the filter and evaporator. Low air flow over the indoor coil, dirty filter, clogged evaporator, or
low on refrigerant. I suggest you to ask some help from professionals or you may bring your unit in near centers that offer 24/7 Aircon Emergency Services.

Either airflow through the coils is restricted such as a dirty filter or fan motor losing rpms, Also could be low on refrigerant.