Posted: Dec 08 2015 at 5:03am | IP Logged

10ecjed wrote: 2012 Frontier 4x4 My heater/defroster blows cold air sometimes, like this morning at 6;30am. Ive been having this intermittent problem for two winters now. Most of the time I can turn off the truck and restart it and it's blowing warm air. This morning I tied that a few times and didn't work. I went back inside the house and ate someting and about 30minutes later I went out and it's blowing warm air. It's like the flap will not move to let the warm air in sometimes. Any ideas? I hope so. Driving me crazy.

Have you checked the radiator fluid level?   For My '13 V6;  To check, first take off the overflow cap, then take off the radiator cap.  If low, leave the cap off the overflow and fill the radiator.  It'll show overfull in the overflow,, but after both cap's back on and run the engine, the level will equalize back down in the overflow.

If coolant level ok, then it may be the heater core valve.

HTH & Good Luck

Posted: Dec 08 2015 at 10:01pm | IP Logged

10ecjed wrote: frontierx376  OK. I will try bleeding the system. Rubble   I have checked the levels and they are fine. What do you mean by the heater core valve? I am not sure if bleeding the system will help, but I will do it anyway. It blows heat almost all the time, when turned on. It is an intermittent problem. If it's a core valve, it seems like it would not work at all. Correct me if I am wrong please.

Look at these Diagram's:  https://www.google.com/search?q=frontier+heater+core+valve&a mp;rlz=1C1CHNY_enUS656US656&espv=2&biw=1280&bih= 628&tbm=isch&tbo=u&source=univ&sa=X&ved= 0ahUKEwiyxPa9-c3JAhWF9R4KHWAZBp4QsAQIOg#tbm=isch&tbs=rim g%3ACeDS7MAk3vg2Ijg3OLrD1RrrYEGM7T3A47NQmHHm-ytMKjUFarJq_19I ZVsdbdOl7w2lHRI3qUYKBkXS5hBIVoCJJ8yoSCTc4usPVGutgEYEAvu5AQLn gKhIJQYztPcDjs1ARouv7g_1rhhYMqEgmYceb7K0wqNRFWrYIvwUFGdCoSCQ Vqsmr_10hlWEVatgi_1BQUZ0KhIJx1t06XvDaUcRVq2CL8FBRnQqEglEjepR goGRdBEN4ByymO8p6SoSCbmEEhWgIknzEQ3gHLKY7ynp&q=frontier% 20heater%20core%20valve

It show's the heater core Valve or where it is anyway.

Check that the Heater Core is Hot, warm, or cold.  If the heater core is Hot,, then it may be the mixing air door.  If the heater core is cold,, or not hot enough,, then you know that the Hot Coolant is not flowing through the Heater Core.

Down load the Service Manual,, it explain's how to change out the coolant.  On my '13, from the factory, the coolant was low in the radiator, but full in the OverFlow container.  I found on mine,, that I had to remove the Overflow Cap, and then fill the radiator up.  The level will rise in the overflow container to over full.  But when I put the cap's back on both the Overflow and the Radiator, after running the engine for a short period,, the Coolant Level equalize's in the overflow to the full level,, or just a little bit above the full level.  To verify the radiator is full,, you have to take the cap off of the overflow First or the coolant in the radiator will come out, when you take the radiator cap off.

That's the way it is on my '13 V6, and I think that it's the same on the '12 V6 as well.  I'm not sure about the 4cyl though.

Even though the coolant was low in the radiator on my '13, I still had good heat though.  And doing it the way that I explained got any air as well.  It really through me for a loop trying to figure out about the low coolant level in my radiator, but I feel like I understand it  better now.  Maybe one of the service tech's took the radiator cap off first and some of the coolant came out.  Seem's likely, cause I've kept a close eye on the System,, and it doesn't seem to have any leak's that I've been able to find.

If your's is still in warranty,, I would take it by Nissan and let them do it, cause it may just be the Air Door that need's to be adjusted.

HTH & Good Luck