A Captain refused a B737-300 with a WING BODY OVERHEAT MEL because of passenger comfort with single pack operation in hot weather and a flight restricted to FL250 in thunderstorm conditions.

Narrative

The same aircraft was assigned to us for three legs. We noted a MEL of the left wing body overheat sensor. After reviewing the MEL; I felt there was a potential safety problem; in that one system failure could cause several events; e.g.; if due to the fact we couldn't use APU except for start; and left pack shutdown; loss of right engine would cause de-pressurization for one; bird strike anyone? OAT in one destination was approaching 100 degree. I noted that all passengers leaving the aircraft; were either complaining of the heat in the aircraft (right pack only) and or some were rather pale and sweaty looking. Limited to 25;000 FT; with some thunderstorms along some of our routes; further limited options to us for safety of flight. After conferring with Dispatch and the Chief Pilot; we determined for Passenger/Crew safety to remove the aircraft from service. Flight was subsequently cancelled. Passengers were accommodated on other flights. Some were upset and I'm sorry about that. However; I made this decision after weighing all parameters for safety of flight. Just because the MEL says it's okay; under certain situations; look a little closer at the implications of system failure related to that MEL.