Sounds like you are trying to create more of a search form as opposed to just filtering. If so, take a look here
http://allenbrowne.com/ser-62.html
for an example. Under Tips for Serious Users you will also find something on applying a filter where a subform is used. It may not apply to you, but it will show the code lines for setting and applying a form filter. The whole site is probably worth your time.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.