LX470 Heater Function Problem (1 Viewer)

[ItGoesTo11]

I have a 1999 LX470 - 160k miles - original owner- garaged - completely stock - well taken care of - no modifications of any kind.

I'm looking for help with the function of the climate control/heater. Here is the problem:

In cold weather, when the car is started dead cold, the climate control immediately turns the blower fan on full blast, as if it's trying to heat the cabin, but with no warm coolant in the heater core. The climate control unit is on auto temp and auto recirculation.
Eventually, when the engine warms the coolant and heat gets to the heater core, the system will heat the cabin and function normally, floating the temp at the prescribed level. So, in essence, the system works perfectly when the engine is warm, except at the initial start when the engine is cold.

Here is what I determined and checked:

It appears the system can't tell there is no heat in the engine/heater core and "thinks" it is warm and immediately starts blowing (cold ambient) air at full blast at first start. I checked the operation of the air mix motor/servo and it appears to be functioning properly. The blower fan is functioning properly. I also used the button combination on the climate control unit to look for errors and the only error showing is "21", which is normal for doing this in a dimly lit garage (sunlight senor). No other codes show.
I also put a laser temp scanner on the hoses going into the heater core and they do register engine temp going in and a lower temp coming out, so that shows there is good coolant flow through the core when the engine does reach temp.
The A/C works perfectly, I checked that operation. And the A/C compressor is not engaged when in heating mode. The engine temp gauge works correctly.

So, what method/device does the climate control system use to determine if there is heat in the engine coolant/heater core? It appears to be blinded to the fact there is no heat in the engine/heater core and acts as if the engine is warmed up. I suspect the device that measures engine/heater core temp may be the problem as the system works perfectly otherwise but appears to be "fooled" that the coolant is warm at first start when it is not.

Any thoughts in what direction to look?

 

[Leandro]

I have a 99 LX also, and i noticed the same when i press the defrost/defog button. basically, doesn't matter the temp, just blows like crazy.
if i press Auto, it works normally (but I'll check again)

 

[AMGAndrew]

I could be mistaken but I think every car I've owned with Auto cliamate control has worked this way. The system is trying to get the cabin warmed up as fast as possible (hence the blower on max) and the way to do that is to be blowing air through the heater core the moment it starts receiving warm coolant. The system isn't smart enough to know how cold and how long it will take for the coolant to warm up so it just has to be programed like that.

Then again, I could be totally wrong.

 

[ItGoesTo11]

I have a 99 LX also, and i noticed the same when i press the defrost/defog button. basically, doesn't matter the temp, just blows like crazy.
if i press Auto, it works normally (but I'll check again)

Thanks, that is indeed the correct function of the Defroster, mine does work like that. My problem is not with the defroster though, it is with the general operation of the climate control system when using heat and in the Auto setting.

 

[ItGoesTo11]

I could be mistaken but I think every car I've owned with Auto cliamate control has worked this way. The system is trying to get the cabin warmed up as fast as possible (hence the blower on max) and the way to do that is to be blowing air through the heater core the moment it starts receiving warm coolant. The system isn't smart enough to know how cold and how long it will take for the coolant to warm up so it just has to be programed like that.

Then again, I could be totally wrong.

Thanks, but no, it should not be blowing ambient (cold) air when there is *no* heat in the engine coolant or heater core. Previously it would slowly increase fan speed in relation to heater core/coolant temp until it's hot enough to blow at max fan speed. This system is smart enough to gauge coolant/heater core temperature and adjusts the fan from 0 to 100 according to the cabin temp setting and coolant temp.
But now it's just blowing at full maximum the second the vehicle is started. This is a new problem to this vehicle, it just started happening.

 

[TX_TLC]

Thanks, but no, it should not be blowing ambient (cold) air when there is *no* heat in the engine coolant or heater core. Previously it would slowly increase fan speed in relation to heater core/coolant temp until it's hot enough to blow at max fan speed. This system is smart enough to gauge coolant/heater core temperature and adjusts the fan from 0 to 100 according to the cabin temp setting and coolant temp.
But now it's just blowing at full maximum the second the vehicle is started. This is a new problem to this vehicle, it just started happening.

Just going to confirm you are correct, this is the correct operation of the LX auto climate control. Sounds like there is a single connection that isn't being made somewhere along the line.
Did it suddenly begin this way of functioning or was it gradual?

 

[benjawi4]

Not discrediting the apparent issue, but imho why bother using the automatic feature at all? When I'm cold I automatically turn the heat up, conversely, when I'm hot I automatically turn the heat down. I love my cruiser wholeheartedly, but it doesn't get to decide when I'm warm or cold hehe

 

[BillZ260]

I use auto mainly for the fan speed control and i use the temp to push more or less air depending on my comfort. I'll say it works wonderfully in my '02 911 Turbo, but has been hit and miss on the LX.

There should be ambient sensors in/on the dash somewhere, maybe fine and test or swap that out first, may have failed, maybe dirty or blocked?

 

[ItGoesTo11]

Just going to confirm you are correct, this is the correct operation of the LX auto climate control. Sounds like there is a single connection that isn't being made somewhere along the line.
Did it suddenly begin this way of functioning or was it gradual?

The correct option of an LX470 Climate Control in Automatic Control is, it will vary the fan speed from 0 to 100 dependent on several factors...the cabin temp set on the display by the driver, the outside temperature, the cabin temperature and finally if there is any heat *in* the heater core.

If there is *no* heat in the heater core, the fan will not run (in heat mode), this parameter overrides the other three factors noted above. Once heat comes into the heater core, then the fan progresses in speed as the heat increases in the heater core.

I am presuming there is a temp sensor someplace that is/has failed, but I don't know where to look or what tells the climate control unit there is heat coming into the heater core...

 

[ItGoesTo11]

I use auto mainly for the fan speed control and i use the temp to push more or less air depending on my comfort. I'll say it works wonderfully in my '02 911 Turbo, but has been hit and miss on the LX.

There should be ambient sensors in/on the dash somewhere, maybe fine and test or swap that out first, may have failed, maybe dirty or blocked?

I don't believe it has to do with the ambient temp sensor, as the fan will not run (in heat mode) if there is no heated coolant in the heater core. The system needs to know there is heated coolant in the heater core before it instructs the fan to run or it would just blow cold air on your feet, which is what it is doing now. This problem of blowing cold air upon cold start began just a few days ago.

I'm guessing it's whatever sensor tells the climate control system there is heated coolant in the core is what has failed, but I do not know what/where that sensor is.

 

[ItGoesTo11]

Not discrediting the apparent issue, but imho why bother using the automatic feature at all? When I'm cold I automatically turn the heat up, conversely, when I'm hot I automatically turn the heat down. I love my cruiser wholeheartedly, but it doesn't get to decide when I'm warm or cold hehe

I've used the Auto function I this vehicle for 17 years, it's worked perfectly all that time, until a few days ago. No modifications have been made to this vehicle recently or before.

The reason to use it is it holds the prescribed temp perfectly, I don't have to do anything, just drive.

 

[ItGoesTo11]

Just going to confirm you are correct, this is the correct operation of the LX auto climate control. Sounds like there is a single connection that isn't being made somewhere along the line.
Did it suddenly begin this way of functioning or was it gradual?

Oh...and this happened suddenly, just a few days ago..

 

[ItGoesTo11]

In doing some more research. I checked the dashboard temperature gauge which shows normal engine temperature rise as the engine warms up. So that appears to be functioning properly.
However the engine in this vehicle (2UZ-FE) has a second sensor, an Engine Coolant Temperature Sensor. I am now wondering if it is failing and the Climate Control might be using that sensor to determine if the coolant is warm enough to activate the fan for heat? I read if it fails it should throw a CEL code, but maybe it's not totally failed enough to trigger the CEL?

Does anyone know if the LX470 Climate Control unit uses the Engine Coolant Temperature Sensor to read coolant temp so it knows when to activate the fan in auto mode?

 

[Leandro]

In doing some more research. I checked the dashboard temperature gauge which shows normal engine temperature rise as the engine warms up. So that appears to be functioning properly.
However the engine in this vehicle (2UZ-FE) has a second sensor, an Engine Coolant Temperature Sensor. I am now wondering if it is failing and the Climate Control might be using that sensor to determine if the coolant is warm enough to activate the fan for heat? I read if it fails it should throw a CEL code, but maybe it's not totally failed enough to trigger the CEL?

Does anyone know if the LX470 Climate Control unit uses the Engine Coolant Temperature Sensor to read coolant temp so it knows when to activate the fan in auto mode?

I don't think that's the same sensor, the coolant temp sensor is used by the ECU to adjust engine parameters, if it's bad, at least you'll get CEL. In any case, that's a pretty simple test with any OBD blue tooth tool ($8 on ebay)

 

[ItGoesTo11]

I don't think that's the same sensor, the coolant temp sensor is used by the ECU to adjust engine parameters, if it's bad, at least you'll get CEL. In any case, that's a pretty simple test with any OBD blue tooth tool ($8 on ebay)

I have an OBD Scan Tool, I'll test it tonight. But I also read it doesn't always trigger the CEL. But there is no other sensor on the engine I can find that would measure coolant temp, so I'm guessing the Climate Control shares that data with the ECU and uses it to vary the fan speed depending on how much heat is in the engine. and thus the heater core.

There IS coolant flowing through the heater core, I know this for sure. So it seems to be a sensor issue as the Auto Climate Control works perfectly once the heater core is warm. The issue is only on cold start until the engine warms up.

 

[AMGAndrew]

10-4. The more you know...

Sounds like you've talked your way through the problem and know more about the system than most of us.

If it is a shared temp sensor and it works enough for the ecu not to throw a code, it's probably not the sensor. I assume the coolant temp signal goes into the climate control module/ecu and that sends signal to the blower resistor which sends signal to blower motor.

I know blower resistors are extremely common fault for a lot of older vehicles. Does your blower/fan speed work on every level in manual mode?

I've learned a lot from this thread and reading into climate control stuff today.

 

[2001LC]

I have a 1999 LX470 - 160k miles - original owner- garaged - completely stock - well taken care of - no modifications of any kind.

I'm looking for help with the function of the climate control/heater. Here is the problem:

In cold weather, when the car is started dead cold, the climate control immediately turns the blower fan on full blast, as if it's trying to heat the cabin, but with no warm coolant in the heater core. The climate control unit is on auto temp and auto recirculation.
Eventually, when the engine warms the coolant and heat gets to the heater core, the system will heat the cabin and function normally, floating the temp at the prescribed level. So, in essence, the system works perfectly when the engine is warm, except at the initial start when the engine is cold.

Here is what I determined and checked:

It appears the system can't tell there is no heat in the engine/heater core and "thinks" it is warm and immediately starts blowing (cold ambient) air at full blast at first start. I checked the operation of the air mix motor/servo and it appears to be functioning properly. The blower fan is functioning properly. I also used the button combination on the climate control unit to look for errors and the only error showing is "21", which is normal for doing this in a dimly lit garage (sunlight senor). No other codes show.
I also put a laser temp scanner on the hoses going into the heater core and they do register engine temp going in and a lower temp coming out, so that shows there is good coolant flow through the core when the engine does reach temp.
The A/C works perfectly, I checked that operation. And the A/C compressor is not engaged when in heating mode. The engine temp gauge works correctly.

So, what method/device does the climate control system use to determine if there is heat in the engine coolant/heater core? It appears to be blinded to the fact there is no heat in the engine/heater core and acts as if the engine is warmed up. I suspect the device that measures engine/heater core temp may be the problem as the system works perfectly otherwise but appears to be "fooled" that the coolant is warm at first start when it is not:

Any thoughts in what direction to look?

Just so I'm clear: "And the A/C compressor is not engaged when in heating mode" is AC light on or not in auto heat mode?

 

[ItGoesTo11]

Just so I'm clear: "And the A/C compressor is not engaged when in heating mode" is AC light on or not in auto heat mode?

The A/C light is lit on the A/C button, so it could engage if the system, tells it to.

 

[ItGoesTo11]

10-4. The more you know...

Sounds like you've talked your way through the problem and know more about the system than most of us.

If it is a shared temp sensor and it works enough for the ecu not to throw a code, it's probably not the sensor. I assume the coolant temp signal goes into the climate control module/ecu and that sends signal to the blower resistor which sends signal to blower motor.

I know blower resistors are extremely common fault for a lot of older vehicles. Does your blower/fan speed work on every level in manual mode?

I've learned a lot from this thread and reading into climate control stuff today.

Thanks and yes, I learned a lot too about something that is relatively stable and never needs much discussion, climate control!

It does share the sensor, but you are correct, the ECT would throw a code if it failed since it is part of the emissions control system. And yes the fan is working normally.

However, good news, I solved the issue. I'll update in my next post.

 

[ItGoesTo11]

[UPDATE: SOLVED] I solved the issue. In researching this issue further, I came across a bunch of articles that all said "check you coolant, lack of heat could be due to low coolant". Well, that doesn't apply to me right? Since the expansion tank on the side of the radiator showed "full". Out of mechanical curiosity I opened the radiator cap and I could see...low coolant! Damn...
I had the timing belt replaced this spring and I think they never filled the radiator fully, but since I didn't need heat in the summer it wasn't noticeable and I don't live in a hot climate so there were no engine temp issues. So I suspect that's where the original issue started.

The LX470 (100 Series) heater core inlet tubes are the highest point in the system, so if there is air in the coolant system it rises to that spot and vapor locks the heater core when you first start up. The water pump does not generate enough push at idle to flush the air, which it why the vehicle would sit idling with cold air blowing for twenty minutes, but would gain heat after we drove it a bit. The faster spinning water pump would flush the air from the heater core. But the process would repeat the next morning after cool down and the air rising to that spot.

(and to make matter worse, the LX has rear heat and there is a "tee" right before the cabin heater core inlet tubes that feeds the rear heater core and those tubes dive *downward* through the transmission tunnel making water flow easier for that core but much harder for a vapor locked cabin heater core. The coolant "waterfalls" through those rear tubes first if there is air in the system.)

So I added about a half a gallon to top it off and took it for a ride to burp out any remaining air. Revving the engine up and down the range as I drove a few miles. That seems to have solved it. I'll know for sure in the morning. But, in essence my climate control system was actually working perfectly, it was trapped air that vapor locked the heater core and kept heat from getting to the cabin.

Thanks for the help in diagnosing this, sometimes it helps to just talk through it.