Random no hear front and rear

[Doug118]

Temps dropped about 30° overnight (12° this morning) and suddenly I have no heat front or rear. Any ideas on what would cause this? Coolant level is fine. It’s very confusing that both worked last night and now this morning neither front or back work

 

[B-train]

Here's how I would go after it:

1. Verify level with cap off reservoir.
2. Start truck and watch fluid level, top off as needed
3. Turn on blower and cycle from 60 to 90F a couple times slowly as the truck warms up and observe if you feel any changes. Or use temp gun pointed in the vent to verify
4. If that fails and temp guage shows heat in the engine, coolant jug full, then maybe power cycle on the system will help. Battery negative removed for 10 seconds or so should do it.
5. Last resort is a bi-directional scanner to see if you can see what it's doing and check for codes.