Reviving this thread.
I just chased my tail for a couple of days, trying to figure out why my heater was blowing cold air.
Heater control valve was leaking slightly, bought a new valve. The old one disintegrated in my hand, so that was for sure bad. Also replaced the 2 short hoses from the valve to the core. Easy peasy, right? Still no heat. Removed cover under dash and put my hand right on the heater core and it was cold. Figured i had an air bubble, bought one of those burp funnels, got a little bit of air but no change. The hoses got warm but not really hot. I've had thermostat get stuck open before, kinda seemed like that might be it. Bought new thermostat, and new heater core since it is original. Replaced thermostat and heater core. Put new foam on the heater core, it seals real good now the old foam was dead.
Engine got up to temp, still no dang heat. Hoses to/from heater core were warm, but not hot.
I really should have figured this out earlier, but i obviously wasn't paying attention.
The dang valve was closed.
I finally noticed after all that work, that the valve was in fact closed. I thought i may have accidentally closed it when putting the vacuum line on. Removed vac line, instant heat. Put vac line back on, valve closed, no heat. Since it is winter time, i just put a screw in the vac line and left it off. I now have nice hot heat, i could dry clothes in the truck now.
So the valve did need replacing, and the thermostat was suspect, but the heater core was likely fine. I am saving it as a backup just in case.
So, now that i have figured out the problem - does anyone know why i would have vacuum on that line when i shouldn't?
I was under the impression that this line should only see vacuum in "off" and "max AC". This problem is fairly new, the heat was working OK last winter. There is a check valve involved within the vacuum circuit with the tank. I'm wondering if that check valve could be bad? I haven't checked out the unit behind the dash yet, could the vacuum lines be routed incorrectly?
It seems that the orange vac line connects from the recirc door to the valve, i haven't really messed with that yet but wondering if that has something to do with it.
Been working on vehicles my whole life, i've had no vacuum before where there should be vacuum, but never had vacuum when there shouldn't be lmao. I'm positive that the valve is installed in the correct orientation, the AC switch is not turned on, "warm" is selected for temp, and it is not in "max AC" position either.
Any advice would be great, it's fine for now with the vac line plugged and disconnected but i'm just curious as to how this happened/is happening. Maybe i installed a vacuum line wrong on the unit behind the dash? I'll check that out come springtime i think, too cold to be messing with it now.
Thanks and have a nice day!
