Help!! No heat in Minnesota

[EGOR46 at aol.com]

My 93 90CS  with climate control is blowing nothing but COLD air.  The blower 
and everything else seems to working OK, but there is no heat.  Where do I 
start  looking?  Worse yet, the driver's side heated seat no longer is 
heated, so when it is 17 below outside it's just as cold inside.  Would 
really appreciate any suggestions on how to troubleshoot these problems.