1994 fleetwood heater

I have a 1994 fleetwood and the heater does not always blow hot air when the climate control is set to max heat. The hoses going into and out of the heater are hot. System is set on ECNO as suggested by the book. Can any one help me solve the problem?

Air mix actuator may be sticking in cold position. Heater core being restricted is also possible. ACM may have codes stored indicating where problem might be.