my 1999 dodge ram van has both fromt and rear air. when i step on the gas my front blower stops blowing air out when it comes back on it is cool air. what could the problem be

Most likely cause is a bad vacuum check valve in the vacuum line that feeds the heating system. That check valve is located on the passenger side of the intake and should be within a few inches of the intake. Pay attention to it's orientation so that you don't put the new one on backwards. (It's a one-way valve.)

thank you