1992-f-350 dually, 460~Not getting any heat. the AC unit engages as soon as the blower gets turned on. only cool air. I have the temp gauge turned to hot. Also blower fan is only working on high. And finally One of the hoses coming from near thermastat housing is warm, the other is cooler. I went to replace the thermastat and there wasn't one in there so I dropped in a 180. any help?

 

I don't think you have the temperature gauge turned to hot.You have the temp.control turned to hot.The blower probably needs a resistor replacement.You'll have to check specs.on thermostat,I'm thinking hotter .The Haynes manual states-"Don't drive the vehicle without a thermostat."
Manual also states,[you do have a manual,correct?]
Could be many things,Both hoses at the heater core should be close to the same temp.Plugged heater core?Possible, blend door issue.
Start with the resistor and go from there.

 

My money is on the plugged heater core. Had that problem one winter when I lived in Canada. Turned on the defroster one morning and it FROSTED my windshield ! Got a new one at Canadian Tire, it lasted less than a year.

 

I have a 88 w a 460. I would think the climate controll is the same. The heater core is just a loop in the system, it dosent care what your settings are at, coolant passes through all the time. The temp selector on your dash goes to a cable like a throttle cable on a lawn mower. This has a bend on the end that just hooks in to a hole on an armature that moves a flap that adjusts how much air passes through the heater core when the fan is on. You should be able to see this under the dash behind the glove compartment. Check to see if the cable is still attatched to the armature. Also, if you follow the cable from the armature back to the controlls you should see a clamp around the end of the outer cable jacket. This determines how much you can move the temp control lever. In my case the cable slipped in the bracket and I could only move the temp lever a bit. Once i put it back where it belonged I had full range of movement. As far as AC goes I have one button that engages the compressor. When I push this button AC will kick on no matter what the other settings are. This might sound dumb but if you have the same button make sure it is out for off. It should have a blue light that is for on. Sorry I cant help with the fan switch. All I could suggest there is to pull the whole unit and flush it out with some electrical contact cleaner and/or replace the switch. hope this helps, Karl....

 

I checked all of the above, it all seems to be working fine. Cable is still operational.
Above the fan under the hood is an air controlled suction valve with arms. The white line going to it is broke and arm is not moving. There is a similar one under the dash that seems to be working fine. Could this be it?

 

Yes - that is part of the problem. You need to replace the blower resistor. It is mounted on the heater air box under the hood. A 180 thermostat is too cold. I believe the proper one is 195. Computer controlled engines do not like cool engine temperatures. I suspect a change to 195 will improve your mileage.

 

I will do all the above give me through the weekend and I will let you know....Latest monday evening.