over heating the condenser inside walls?

i have an upright freezer model WF14FC2CW.BLA serial WBS2126634 white westinghouse that doesnt freeze, the unit runs the freon pressure is 4psi on the low side, at the starting point of the unit condensation starts normaly on the evaporator, after about 20 minutes of runing my freon pressure begins to raise and the sides of the freezer get too hot, my condensation on the evaporator begins to drop. These takes me to believe on the need of an external condensator, but not sure so i would like to know what you recomend, thank you for your suppor.
sincerrely yours.
marco acosta
dba. acostas refrigeracion
tijuana mexico
acostasrefrigeracion@yahoo.com.mx