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All,

Hopefully someone will have some idea of the cause of this issue and if it's something I can fix myself (~7 on the handiman scale - but definately not a car mechanic) or have to let a toyota/hvac mechanic work on it.

Even after my engine warms up, my hvac blows cold air until the vehicle is moving. And after it is blowing warm air, then the car stops, it quickly starts blowing cold air again.

The vehicle is a 2007 FJ.

Not sure if it is related, but I replaced the resister pack last fall because the fan wasn't working on low speed. It was heavily rusted.

Thanks,

Phil
 

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Sounds like you have air in the system and the heater core is only getting hot fluid at speed. Purging air from the heater core can be a pain, but try power flushing the cooling system, then draining the radiator and block and adding antifreeze to appropriate level.
 

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All,

Hopefully someone will have some idea of the cause of this issue and if it's something I can fix myself (~7 on the handiman scale - but definately not a car mechanic) or have to let a toyota/hvac mechanic work on it.

Even after my engine warms up, my hvac blows cold air until the vehicle is moving. And after it is blowing warm air, then the car stops, it quickly starts blowing cold air again.

The vehicle is a 2007 FJ.

Not sure if it is related, but I replaced the resister pack last fall because the fan wasn't working on low speed. It was heavily rusted.

Thanks,

Phil
Here are some youtube videos on how to flush your heater core. I did this on my Grand Cherokee and an F150 with amazing results. You will have to purge the air out of the rest of the system even after doing this so keep some 50/50 antifreeze handy to keep it full. If it has not been done I would pull a complete flush after this to to clean things up.

https://www.youtube.com/results?search_query=fj+cruiser+heater+core+flush
 

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It sounds like the coolant is low.Allow the engine to cool enough to remove radiator cap(not coolant bottle cap). Fill radiator to neck. Top off bottle and then run and see how heat is.If this doesn't do it pursue other routes.If it does then you need to find out where the coolant is going(leaks etc...)
 

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Stop and do some simple troubleshooting. From your statement above you have been driving your FJ. Correct ? 1. When cold verify the correct level in the overflow bottle and the radiator. 2. Start your engine and turn the heater heat setting to high, continuously observe the temp needle making sure it does not go into the RED. If this goes well and it gets up to temp and everything looks good let then it run 5-10min. Shut it off and let it cool down to ambient temperature. Then start with step 1 again. Every time your engine cools down it should suck coolant from the overflow bottle keeping the radiator full. Eventually the system will be full every time you remove your radiator cap. Throughout this process keep the overflow bottle at the full/hot line. If this works your done If not then you can proceed with more advanced troubleshooting. The resistor block is used for fan motor speed control , your fan runs right?
 

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(snip)
Even after my engine warms up, my hvac blows cold air until the vehicle is moving. And after it is blowing warm air, then the car stops, it quickly starts blowing cold air again. The vehicle is a 2007 FJ.
Lets back up even further, and consider the possible root causes of a lack of heat from the HVAC system:

1. The engine coolant temperature is too low.
Possible causes:
a) Engine thermostat missing, or stuck wide-open
c) Extremely low ambient temperature + low engine load

2. There isn't adequate hot engine coolant circulating through heater core.
Possible causes:
a) Extremely low coolant level in engine cooling system
b) Restriction in heater core or engine block water passages
c) Collapsed or kinked heater hoses
d) Water pump flowrate low, or water pump drive belt slippage problem
e) Cooling system not properly bled to remove trapped air

3. Air isn't being directed through heater core.
Possible causes:
a) Blocked cabin air filter
b) HVAC duct blend flap sticking
c) Improper speed of HVAC fan

Also, you said: "And after it is blowing warm air, then the car stops, it quickly starts blowing cold air again".

Do you mean it stops blowing warm air every time you bring the vehicle to a stop, or every time you turn the engine off, and then re-start it?

What is the outside temperature when you notice the lack of hot air?

Finally, where is the needle on your coolant temperature pointing when you notice the lack of hot air?
 

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Strong post FJTest . You covered everything I was also thinking. Just for reference, having the engine temp indicator information, could be key, to ruling out one direction
 

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Strong post FJTest . You covered everything I was also thinking. Just for reference, having the engine temp indicator information, could be key, to ruling out one direction
Yup, a shortage of hot water = shortage of hot air. Hopefully, the OP will provide some additional info to narrow down the search for the culprit. Temp gage indication will tell a lot, assuming the cooling system is full of coolant.
 

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Discussion Starter #9
Sorry for not following up. Car was unavailable to me today. Also didn't get any notification that my post had replies, so I'll need to look for the setting for that too...

To clarify a few points.

The outside temp is single digits. Therm gauge reads cold the needle moves to normal as the engine warms up. The blower is fine at all speeds but will blow cold air instead of warm if the vehicle isn't moving. This is after the engine has warmed up. I have not checked the coolant or the air filter, I'll do that tomorrow.

Thanks,

Phil
 

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Checked the radiator and overflow resevoir this afternoon. Radiator was about a liter low and the resevoir was all but empty. I topped both off and will see if that resolves the problem. Thanks for the assistance - hopefully, that is all that needed doing.
 

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Checked the radiator and overflow resevoir this afternoon. Radiator was about a liter low and the resevoir was all but empty. I topped both off and will see if that resolves the problem. Thanks for the assistance - hopefully, that is all that needed doing.
It's unlikely that simply being "a liter low" on coolant would cause your symptoms, but I think you may find that you are actually more than a liter low after you heat-cycle the engine several times. Just topping up the radiator and filling the reservoir won't automatically purge the air that may trapped in other parts of the cooling system. The purging of trapped air will usually happen automatically over the next few driving cycles as the coolant and trapped air expand and contract and pull additional coolant out of the reservoir and into the cooling system. So, over the next few driving cycles closely watch the coolant level in the reservoir, and continue adding coolant to the reservoir as needed. Keep track of the total volume of coolant that you add to the system, and let us know what it was.

The next two questions are:

1. Why did you not notice that the coolant level in the reservoir was dropping to the point of being empty? Only two things will quickly kill a Toyota engine: lack of oil, or lack of coolant. Make it a habit to check both EVERY time you fill up your gas tank.

2. The shaft seal on the water pump is designed to be lubricated by coolant; so the water pump continuously "leaks" a tiny amount of coolant (a few drops a week) to keep the seal lip lubricated. Therefore, the coolant level in the reservoir will slowly drop over a period of months. If the rate of coolant loss is greater than this, you have a leak somewhere in the cooling system that needs to be located & fixed.
 

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Just keep checking like I posted. Being a 2007 it will have lost a little over time . Mechanical seals have a very minute leakage rate. You need to check the overflow bottle until the level remains steady then you can check every few months. Sounds like your good.
 

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All,

Hopefully someone will have some idea of the cause of this issue and if it's something I can fix myself (~7 on the handiman scale - but definately not a car mechanic) or have to let a toyota/hvac mechanic work on it.

Even after my engine warms up, my hvac blows cold air until the vehicle is moving. And after it is blowing warm air, then the car stops, it quickly starts blowing cold air again.

The vehicle is a 2007 FJ.

Not sure if it is related, but I replaced the resister pack last fall because the fan wasn't working on low speed. It was heavily rusted.

Thanks,

Phil
Looks like you have a blockage or air bubbles in the heater core.
 
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