I can't find the Pressure switch on my furance it's a nordyne m1m series

It should have a diagram that ID`s each part and shows where it is,,

Most of the M1M Nordyne units did not have a pressure switch but about 1500 or so of them did leave the factory with a HSI/pressure switch setup. A complete factory service manual is provided at the link below. It covers both styles of burners available on the M1M units. Becareful!! If you do not know what you are doing just do not do it since this the HSI version of this unit can be a little touchy to service and adjust. The standing pilot unit is strait forward no problem.

http://www.nordyne.com/Literature/690a.pdf

The manual does NOT tell you how to remove the limit switch.