No heat on FAN level 4

[BoatDriver]

I have heat on fan levels 1 through 3 but on 4 it feels cold. Does anyone know why this is and please help. I replaced the thermostat and mt coolant is full.

 

[eddie baller]

When u change the temp setting from hot to cold doesit make a clicking sound? If so ur blend box might be bad there is a write up on how to change it on here.

 

[BoatDriver]

no clicking noise when I adjust from hot to cold.

Thanks