Have a Ducane 3 ton hpump we installed today, works fine in cooling mode but in heating mode it drops out the low pressure switch. Pressures look good on the line set. Is there any reason it would work fine on cooling but drop out on heating. Reversing valve seems to be working okay. Get plenty of heat on the hot gas line. Compressor will only run for a couple of minutes in heating mode and then drops out. How do I check if it is the switch or another problem. I really don't feel like recovering the charge, changing the switch and finding I have a blockage or restriction somewhere. Temperature around here is only about 45 degrees right now so tough to get the charge just right until it warms up.