I have a 1999 F150 5.4L with 184k that only blows cool air. The vent switch works fine, I can change from defrost to floor vent. I can also change from "hi" to "lo" so the fan seems to be working. The problem is the air temperature. Cool air blows no matter where the temperature dial is.

The problem started a couple of weeks ago when I was running the a/c full bore. Sometimes the a/c would be on, other times there would only be cool air blowing.

As fall approaches, I am looking for a fix!

Any ideas on what is causing this?

 

I used to have the same truck as you. Mine had the manual climate controls; fan speed, temp and vent select *****. I don't know if the 99's were avail with electronic climate control. Pull your temp selector **** and look at the back side of the **** and check to see if it is cracked on the back side. If it is, the **** can't grab tight enough to turn/adjust the blend door that controls your air temperature, replace the ****. You can also get a pair of needle nose and grab the plastic shaft on the climate control that the **** sits on and turn the shaft. If your air temp changes replace the ****. If air temp does not change maybe the cable to the blend door came off either at the **** end or at the blend door or the blend door itself may be broken.

The climate control console is fairly easy to remove if it comes to that. Gently pull the trim bezel around the stereo and climate control off. It's held on by basic trim clips. Once you have that off it should only be 4 screws holding the climate control console on.

Hope this helps you out or at least points you in the right direction. Good Luck!

 

It's funny you mention the back side of the **** not grabbing the plastic shaft. I had this happen about 4 years ago on this truck and had to replace the ****. When turning the temp ****, I can feel resistance like the **** is turning something in the climate control console.

I will look into the blend door fix. I had the blend door in mind when I wrote my previous post but I wasn't quite sure.

This morning on my way to work I figured I would give the heat a try in hopes warm air would blow out of the vents. I was able to get a little warm air but the problem continues...

 

Can't hurt to take the **** off and take another look. If you tried adjusting your temp and got a little bit of change it could be the **** just isn't grabbing enough to get the full change in temp if it is not cracked on the back side. Try changing the temp control with a pair of needlenose pliers to see if you get your full range of temp. If that doesn't work look at the cable and blend door.

I mentioned the **** because I worked as a service advisor at my local Ford dealer for a little while after I retired from the Navy. An older lady came in one day pi**in' vinegar because her A/C was not blowing cold air in her truck (same generation as yours) and she had her truck in previously for the same problem and still was not fixed. I wrote up the service request and sent her on her way. Before a tech took her truck in I decided to take a look. Turned A/C on, tried adjusting temp and no joy, I took the **** off and say it was cracked. I adjusted the temp using needlenose and wouldn't you know it blew cold air and hot air. I replaced the ****, worked like a champ. I call her back 10 minutes after she left to tell her her truck is ready. She came back, still mad, and said, "It better be fixed right this time." I handed her her keys and told her to go check. She came back a few minutes later much calmer but still trying to sound mad and asked what was the problem. I told her, she could not beleive it, so I showed her the old **** and sent her on her way. Glad I didn't see her again.

Anyway, sorry to get long winded for something so short and simple. Let me know if I was able to help you. If I can't hopefully someone here will be able to. Good luck!