Front heat not working

Alright, I’ve got a challenge and I’m looking for advice. I’ve searched and haven’t seen anyone else with this problem. The front heat doesn’t start up when it’s cold. The rear heat always works. Eventually when the truck warms up enough something kicks in and it starts working normally. The colder it is outside the longer it takes to start. I can switch between fan directions (floor, center, defrost, etc) and I hear a slight clicking but no air is blowing. I have replaced four parts of the system: blower resistor, blower motor, selector switch, and a relay under the hood. After each replacement the system continues to function as before. So there is something that doesn’t work in the cold and eventually kicks in once it warms up. I haven’t timed it but it’s probably 15 minutes at zero degrees. And the last piece of info. The hot/cold adjustment knob doesn’t work. It’s either hot or cold with no middle. I don’t think that’s related to the slow start but maybe? Any advice??

The right way to do this is with a wiring diagram and a voltmeter. Check for voltage at each connector from the blower motor back to where you know you have power. But you have to freeze your butt off doing this while it isn't working.

The Rube Goldberg way to do it is to buy a bunch of Scotchlok connectors, wire, 194 bulbs with sockets, and make a holder for the sockets. Then wire each bulb to one step of where you would measure with the meter. If the one from the live blower motor wire to ground lights up its bulb, the others should all light up and the motor is bad. Make sure all the bulbs are connected to a really good ground.

Update on this problem. I bought the wiring diagram book (about $30 used) and studied the components in the circuit. There actually aren't too many parts involved in the blower motor control. I found one small relay that I had not yet replaced and this turned out to be the problem. A $10 relay was freezing during the cold weather and not functioning until it warmed up.

It took about two years, a few hundred dollars in parts and lots of time investigating and working on it but I finally fixed the issue.

Good to hear and thanks for the follow up. What year is the truck?

Glad that worked out so easily for you. Thanks for the update.

Mossback - the truck is a 2010 XLT

Jonneyo said:

Update on this problem. I bought the wiring diagram book (about $30 used) and studied the components in the circuit. There actually aren't too many parts involved in the blower motor control. I found one small relay that I had not yet replaced and this turned out to be the problem. A $10 relay was freezing during the cold weather and not functioning until it warmed up.

It took about two years, a few hundred dollars in parts and lots of time investigating and working on it but I finally fixed the issue.

Click to expand...

Which relay was it that you replaced? I am having the same exact problem with my 2016.

Just a heads up with others reading this thread, my front blower motor quit working on me, but rear was fine so I used that until our winter lull ended and I needed the defroster badly. I started by the book, and Q & A from here. I went to pull the plug at the blower to check for voltage and the plug was still connected, but loose. Quick, simple fix and I was happy, happy. So were my frozen fingers...