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Posted: 12/14/2010 4:09:00 PM EST
I have a 2005 nissan frontier. The heater has been giving me trouble. When the truck is standing still there will be cold air blowing out of the vents even when the engine is fully up to temp and the heat is set on the highest setting. Once I tak off and the truck is rolling down the road, it will start blowing hot air within seconds. If I stop at a redlight, in just a few seconds it's blowing cold air again. It also seems like the faster I'm going the hotter the air from the vents. Driving through town at 30 to 40 mph it will blow fairly warm air. Going 70 on the highway, it will blow very hot air.

So, does anyone know the cause and how to fix it? Your insite would be much appreciated.

Thanks,
Adrock1
Link Posted: 12/14/2010 4:30:36 PM EST
[#1]
sounds like a clogged heater hose or core to me.. When you are driving, pressure bulids in the system as the rpms increase. drain the coolant then take off one of the heater hoses at the core. Take your hosepipe and try to run water through it. if it comes out rather forcefully then you are all good in that area. if not then you have a clogged core. Check to make sure you have aadequate water flow to the heater lines themselves. make sure your truck is cold, and keep running water in the radiator, until the thermostat opens. it should flow out of one of the hoses..
Link Posted: 12/14/2010 5:24:27 PM EST
[#2]
Link Posted: 12/14/2010 9:27:25 PM EST
[#3]
Yeah, sounds like your low on coolant.
Link Posted: 12/15/2010 6:19:01 AM EST
[#4]
I had a '91 Civic that had overheated (bad radiator) and subsequently cracked its head gasket.  I was unaware of this, as the crack only let water into the combustion chambers, not into the oil circuit.  Eventually, when enough coolant had been burned off, I noticed no hot air coming from the heater core anymore - the coolant level was low enough to have drained the heater core.  An HC test on the exhaust confirmed that the engine was consuming coolant, so a new head gasket went in.  

So, check your coolant level first, and check into where it may have gone...
Link Posted: 12/15/2010 1:28:04 PM EST
[#5]
I checked the coolant today. Resevoir was full with the vehicle all warmed up. It was doing the same thing on the way to work this morning, but then on the way home, it stayed warm wether I was moving or not.

Another observation is that it was blowing warm even at a standstill as long as I gave it a little gas and revved the engine up a little.

Adrock1
Link Posted: 12/15/2010 2:14:05 PM EST
[#6]
Does the coolant temp gauge do anything unusual?

Does that engine's water pump have plastic blades? You may be missing some blades, so very little coolant circulates at very low RPM, but does circulate a bit at higher RPM. Normally you would see engine temps going way up in this condition, but with the cold air temps, perhaps not.

Remove the rad cap (engine cool), start engine and let it heat up until the thermostat opens. You should see quite a bit of coolant flowing back into the rad from the engine at idle.
Link Posted: 12/15/2010 3:38:22 PM EST
[#7]
Not to hijack, but my truck (chevy 2500) will blow cold air on one side of the truck and heat on the other. I could have th eheat on full blast and one side will be blowing the ac. Why does my truck do this???
Link Posted: 12/15/2010 3:59:32 PM EST
[#8]
Link Posted: 12/16/2010 4:48:01 AM EST
[#9]
Quoted:
Unfortunately I have never worked on the HVAC system of a Nissan Titan, if you have a service manual you may want to look up the blend door actuator and find out if it is electric or vacuum powered. I have seen lots of Fords with vacuum powered HVAC systems do funny things, more often that not they will either get stuck on defrost or drop to defrost under acceleration.

I had a work truck with a minor vacuum leak in the HVAC, anytime you accelerated it went to defrost until you had more vacuum on the manifold.

For the GMC, does the truck have dual zone climate control? If not you probably have a vent door stuck somewhere in the plenum, good luck with that.


Does sound like something jacked in the blend-air system. The blend air works by mixing cold and heated air in the hvac box..usually a blend door opens/closes partly or fully..and mixes air from the heater core..and AC side to achieve the desired temp. Could have a mechanical controlled door..vacum..or electric. Changing temps with engine speed sounds like a vacum issue to me..but I ain't familiar with Nissan.

If it is a vacum operated system..may have a leak..bad check valve..bad dashpot..bad dash controller..etc.

Link Posted: 12/16/2010 6:15:39 AM EST
[#10]
Heater core is plugged.
Link Posted: 12/16/2010 1:39:45 PM EST
[#11]
Well, made some more observations today on the way to and from work. I had heat at all speeds and RPMs. So now it's not acting up. I hate this shit because I know what will ultimately happen. I'll take it to nissan, and they won't be able to replicate the problem. So they will guess, try to charge me a bunch of money, and probably not fix the right problem. Ugh!!

I have a long road trip coming up in about a week to florida. I'll see how it behaves on the way. At least if my heat totally craps out, I'll be in florida. At least until the return trip

Adrock1
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