During summer months the temp in the cab gets extremely hot with the heater off.It is a 1997 super duty with no AC.

 

If the heat is excessive and otherwise unexplained one thing to check for is retarded timing or similar. The unburned fuel will get the exhaust, and cats, really wound up cherry red or at least a whole lot hotter than they should.

 

Probably because it's summer....

 

If there is no heater control valve, the hot water is still circulating through the heater core in the dash, all summer long. You can add a ball valve to the heater hose, and turn off this water flow in the summer. This will make your A/C more effective, too. Some people add a vacuum-controlled valve and plumb that into their HVAC system so that it is automatic.

Also, look for air leaks or dislodged rubber grommets that might be letting hot air into the cab thru shifter holes, etc.

 

We used to have a lot of old body style Ford pickups on the family farm. There are 2 different ways to disconnect your heater core for the summer months.

1. Cut the in hose and put a valve in the line.
2. Pull both hoses from the heater core and connect them together with a hose connector.

Also check your blend door. I had a 95 f150 that wouldn't go to heat in the winter. Tore that dash inside out one year and found one of my sons toy farm fence panels had fell down the defrost vent and was holding the blend door open.