Dear Felix
Unfortunately, the [PRODUCT, ex. Cold Elite Air Conditioner unit you installed in our premises] on [DATE, ex. June 1, 1998] is malfunctioning. [STATE NATURE OF MALFUNCTION (S), ex. Instead of cold air, the unit expels room-temperature air.]
I would like to arrange an appointment for service under warranty #[WARRANTY NUMBER] (a copy of which is enclosed, along with the sales receipt). Please call [NAME, ex. me] at XXX-XXXX so that we can determine a mutually-convenient time.
Regards
Lydia