I will assume you are talking about evaporator --a few reasons restricted air flow coils dirty -air filter clogging --fan not working or operating properly --low on freon ---turn fan on and with a spray bottle mix water and a little liquid soap and spray coils the fan will pull mixture thru coils keep spraying do not wipe the coils you can get injured and also damage coils an replace with new filter if still freezes over will need to check freon level and fan operation
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I will assume you are talking about evaporator --a few reasons restricted air flow coils dirty -air filter clogging --fan not working or operating properly --low on freon ---turn fan on and with a spray bottle mix water and a little liquid soap and spray coils the fan will pull mixture thru coils keep spraying do not wipe the coils you can get injured and also damage coils an replace with new filter if still freezes over will need to check freon level and fan operation