I have a 2000 IH 9400i and know there should be an cab air filter some where,have an idea its under passenger seat or is that something else,has a vent there on door side. Is there a filter in htere by chance?

 

It's probably near the floor on the passenger side, up by the firewall. Wherever the intake vent is for your heating and AC system is, the filter is nearby.

 

Under the passenger seat, in the HVAC unit.

Best thing to do is take the pass. seat out, remove the top cover from the HVAC unit, pull out the fiberglas filter and wash & dry it.

While the filter is out. use an air blow gun to blow all the dust & dirt out of the heater core & AC evaporator.

If that doesn't get your heat working properly, post again, there is another "quirk" in those systems that may be preventing full heat (or AC) output.

 

Thanks for the info. was wondering where things were kept on this truck. I purchased used last feb. 08' and has been pretty good truck to me,but never got any book on things on the truck and where they are located which, iam gradually figuring out for myself.