Heater not hot.heater fan only works on full - Sentra Nissan Cars & Trucks

Sounds like heater core

Most likely it is the heater control valve that shifts air from blowing across your heater core to your air conditioner core.

If your fan works and your car is fairly new..meaning your heater core isn't dirty and full of craap...then it is the climate cotrol valve.
If you are lucky, it might be a thermostat that is bad and blocking hot water from entering your heater core. Bottom line, if hot water doesn't circulate thru that little heater core, you won't get heat.
You might be able to look under the hood and grab the hot water lines that go thru the firewall and feed your heater core. If they feel cold to the touch after engine has warmed up, then you aren't getting circulating water to the heater core. If they feel nice and warm, then the heater core is fine, but your climate control valve has closed off the fan that blows across the core to disperse heat into the cabin

may be something plugging the heater tube itself, maybe a rodent has set up camp, fan resister works both cold and heat fan speeds, unless they have a resister for cold and hot which I have not heard of.

If both heater hoses are hot, and the radiator is full of coolant, it may be a blend door problem under the dash.
The blend doors direct air thru the heater core and out thru the vents.
It may still be under Ford warranty.

its in the heater box, right dash.
1: fan blow full speed? (heater fan?)
2: does engine hold and reach 180F ?
3: when you slide the hot cold lever. does its end of able move?
and does it move the damper flap from closed to open(open is hot)
knowing these simple facts, allows diagnosis.

Need to check the coolant level to ensure that it is full. If full, check the hoses going to the heater core. Both hoses should be hot. If one is much colder than the other, you have a stopped up heater core. If that is fine, check to be sure the engine is getting as hot as it should. A stuck open thermostat will not allow the coolant to heat up enough and not blow hot air. If all that is good, check the blend door under the dash. It may be getting stuck in between the hot cold positions and not allowing all the air to flow over the heater core.

Probability 1) The thermostat is probably stuck open, coolant is not getting hot enough from the engine to provide heat.

Starting from cold, allow the engine to run and warm up. While doing this, feel the upper radiator hose - you should be able to feel the coolant heating up to the point the hose is uncomfortably hot. If it gets that hot, then go to next step.

Probability 2) The heater core flow is restricted, not allowing full flow of coolant into passenger compartment.

There are 2 smaller heater hoses that run to the firewall. Are either of these hoses getting hot? Both sides hot indicate full coolant flow. Both sides cool indicate heater control valve not opening fully.

When the coolant in the heater core is hot from the engine and your fan is on hot air will blow through the hot fan coil, i figured it out, when i stepped on the gas i could here the coolant squeezing by the control or limiter valve, because the higher rpms make the belt spin faster which makes the water pump pump harder causing more pressure, so when u idle that hot coolant will cool down from the fan blowing on it, u need to find the control valve and open it up to full blast, then hot coolant will always be flowing through your heater coil. ;)

The heater core is possibly blocked or the temperature adjuster is not working.

First check the controls to be certain that the temperature aduster is working and the flaps/doors that direct the flow of hot air are working.

If they are..........

Check heater hose temp. If one is hot and one is cold, you are not getting flow through the heater core.

Bleed it to remove an air blockage.
If that does not work, flush the system.
If that does not work, replace the heater core.

Karl at topgunwon.com

Replace the temp control on this car, it should be electrical control not cables.