My hvac/heat is having issues. My truck is an 1996 Ranger. the hvac will only blow cold if it is only on MAX A/C. If i turn it over to a/c it automatically changes over and blows HOT heat. then last night it got alittle cold so i turned the heat on and it will only blow hot heat out....if i change the climate to try and have cool and hot it doesnt do anything....so it will only blow if its on max ac for AC and the heat....i cant get to be just right...i turn it on and jusdt acouple mins it is too hot to stand..so i have to turn it off then it gets cold...theres no in between...guess i have to ride with the windows open with the heat on full blast if no one is able to help me. I changed the heater valve under the hood last christmas....theres nothing else i know of to do except take out the climate control piece and install an digital climate control. let me know if you know what my problem may be. thanks

 

There are two things happening here, one is normal, one is busted.

First, when you switch to MAX AC, it bypasses the heater core so you can't have heat at all.

Second, your blend door actuator isn't working. I believe this is vacuum operated and is a common failure. I don't know the fix but it is common here. When it fails, it fails to full heat.

 

On most 95+ Rangers, the blend door is moved by a small motor through a gear reduction. Some years have a cable arrangement. The small square pin at the top of the door can break, disconnecting it from the motor actuator. Replacing the blend door is a big job but there is a workaround that may get it going again.

http://www.blenddoorfix.netfirms.com/