Heater/Blower motor issues

What's going on everyone...I've had my 1990 B series for a few months now, since I've had it I had some heat issues. The truck hit opperating temp on my gauge but my heat blows Luke warm now if I let the truck sit and idle for a while it will blow pretty hot but as soon as I start moving it gets like warm I already replaced my thermostat. And still the sane issue. Now the other day I went out started my truck went to defrost my windsheild and I had no blower motor fan on any settings I was thinking a motor resistor but the resistor doesn't control the highest setting and it's not working on any speeds some help with these issues would be greatly appreciated

It could be the switch. My fan won't blow at all unless the switch is on high, and even then its barely blowing and its just luke warm. Also the luke warm I think could be possibly due to slight block in the heater core maybe... as far as I know the switch for the fans in these trucks are notorious for going bad my last B had the same problem as well.

First, the thermostat should be 192F/195F if you want to get decent heat. I use Stant brand, and that 192F/195F thermostat year-round in Arizona. Some slip in a piece of cardboard for winter to block off half the radiator. Also, after your thermostat install, did you bleed out ALL the air out of the cooling system? Very important. Check coolant level every other day for a while and top off. I actually jack up the front end and run with cap off to bleed out the air.

OK, get underneath on passenger side. You need to see if there's positive voltage (with the fan switched on) in one of the two wires going to the fan motor itself. You'll need a test light - better would be a $15 DC voltmeter/multimeter and first see if the fan is getting voltage. You could also pull out the fan and jump that directly.