My whole HVAC system in my 04 Screw Lariat is litteraly blinking. As if someone installed a christmas flasher in the system. Power on or off (particularly distracting at night when dash lights are illuminated). Have checked the owners manual as I am not a true tech but a very proud owner. All indicated fuses appear intact. Not a real diode or relay whiz so if any of you have an idea please let me know. This is the electronic controls model. Seems like a relay problem to me. Blower, clutch, door, lights, display,fan & compressor all come on pause off pause on pause off pause. Really annoying that the June/July swelter season is upon us.

 

I have an 04 that did the same thing,I was driving home one night the h.v.a.c. pannel started flashing on and off then went out, pannel went black or blank ,next day did not work in morning but ride home that night came back on and has worked ever since.The only thing I can tell you was a relay on passenger side kick pannel was clicking while this was happening.Listen and check to see if you hear a relay clicking on your truck possibley bad relay !!!

 

Thanks very much for adding in Tom. Glad yours came back to life. Actually I too have the clicking noise. Its actually the blower motor relay doing its job. Man I wish this was that simple. I got excited when I pinpointed the noise too. I was like cool! Relay! Ok check book which one.... aw dangit! Blower relay of course it cuts in and out when power is applied and fan is selected. Shux! Seems like there is something else maybe a ground that allows so much heat to build up then open contact, cools quickly then closed, cycle cycle cycle cycle. Its driving me nuts but I think I'll hafta bite the bullet and call this more of a DIY than I can trouble shoot without good direction.
Still open to all suggestions. Thanks again Tom!

 

Update! Fixed I think! So something just told me to simply reboot by discon/recon. the battery. So far so good! Hope this works for the next guy. A whole week of what am I gonna do down to a simple battery redo/ Humph. Now I gotta get the sweat stains off my leather.

 

So my dad called me up asking this same exact problem and asked me to search our infamous forum of help and I found this post. So I told him to disconnect his battery to reset his computer just like you did. It worked!! Thanks again F150online!! Especially since we're hitting record breaking temps. this summer 105+. Thanks again!!!

HE also has an 04 F150 Lariat screw

 

Awesome andrzej77ff! Glad I could contribute. As you can see I rarely step in usually only when trouble arises. This place is great!