The Mystery of the Missing Heat

[Dunnik]

Hi all, new to the forums and new to my 1-owner, dealer-serviced 2006 LX 470, which I bought, sight unseen, from Vancouver, BC and had it shipped here.

From day one, it's had severe problems producing heat. Symptoms are, it blows cold in any and all settings, and it can take 40 minutes or more to produce anything remotely resembling heat. The rear heat functions as well as the front, which is to say, not at all: rear on/off, auto/manual, no effect. The vehicle is capable of producing heat...sometimes...maybe after 40 minutes.

So far, the following has been attempted, with no result:

- new thermostat
- two coolant flushes, confirmed no air in the system
- new heater T's and heater core flush (a tip thanks to searching this forum)
- heater core inlet and outlet temps are within factory specs, so seems unlikely it's that
- new clutch (blower) fan

What else is there? I'm at a loss. Your thoughts are welcome. We'll see if Lexus Downtown here in Toronto is also stumped, they've kept the vehicle over the weekend (I've kept their loaner). It's been in and out of their shop four times now. Fortunately this dealership is one of the good ones and has not given up, as many indies might, at this point.

P.S. Ironically, I bought this vehicle for use only in the winter, and what better vehicle to tackle anything a Canadian winter can throw at you than a Series 100 Land Cruiser? A vehicle with heat would be better. Hoping to get this fixed before winter ends - actually, hoping I can just get this fixed no matter how long it takes. Otherwise happy with my purchase: other than a blown telescoping steering wheel motor and this heat issue, the truck is sorted.

 

[TheForger]

Do you have rear heat? If so are you getting any heat out of those rear vents after adjusting the rear AC controls? Maybe it's the little blender door

 

[Dunnik]

Do you have rear heat?

Rear heat functions as the front does, which is to say, it doesn't. Should have included that key bit of info in the post, I'll update thanks.

 

[FxFormat]

Blend door not operating correctly or ambient temp sensor has gone bad. If you're sure the heater core isn't clogged and there's no air in the cooling system and the thermostat is a good one and not a junk one that's stuck open.

 

[TheForger]

ambient temp sensor has gone bad

^This is a good idea as well. I did this and it did improve the AUTO function of my AC system. It's also very easy to do and took maybe 5min. Check my post HERE for a couple pics of what mine looked like.

 

[Biga27110]

Air mix servo others have called the blend door.

 

[TheForger]

Well hang on I'm pretty sure there is a servo for the rear AC as well and that system is separate from the front system? Correct me if I'm wrong. If so and you don't have heat in the rear, the likelihood of front & rear servos both failing is slim.

That is a really clean truck how many miles does it have?

 

[Dunnik]

Thanks all, will check those ideas out. Truck has 250,000 km on it (155k Freedom Miles), and is otherwise very clean, especially underneath, which was really what I was aiming for: a rust-free example.

 

[CloudCity]

Truck has 250,000 km on it (155k Freedom Miles)

You know how to work a room better than Eddie Murphy.

 

[Austin Hot Shoe]

Not the same problem, but similar.........had heat at vents but none at floor.........carpet covered the floor vents, it looked like it had been like this since new, the carpet was not properly tucked behind floor vent. Took me 4 years to figure this out.

 

[Dunnik]

...carpet covered the floor vents

I saw your post in fact when I did a search, alas no, air blows strong in the footwells, no blockage.

 

[BullElk]

^This is a good idea as well. I did this and it did improve the AUTO function of my AC system. It's also very easy to do and took maybe 5min. Check my post HERE for a couple pics of what mine looked like.

Does cleaning this help the AUTO function only?

Also, regarding possibly changing a bad thermostat......If the T stat was bad wouldn't you already know it by just checking coolant temps? If coolant temp is 185*, like it should be, then its good and air should be properly warm, correct?. What would coolant temp be if its stuck open?

 

[Dunnik]

Cleaned cabin ambient temp sensor, wasn't too dirty.

No result.

As there doesn't seem to be anything more to be done, the Lexus dealer is returning the vehicle.

Refuse to believe this is unfixable. Any other thoughts or suggestions would be most welcome.

 

[TheForger]

Huh, that's frustrating...Makes me think your heater core is messed up in some way. From the sound of it this is less of a problem of hot air not coming through the vents, and more of a problem of not producing hot air in the first place.

 

[kruisinkid]

if the front and rear heaters are not producing heat it has to be upstream. i would suspect at the T's. how did you measure that the IN and OUT temps are to spec for the front core? that could just as easily be an air bubble that is at the spec temp. air will actually get much hotter much faster than water in the system. i would park on a severe incline and run the truck with the rad cap off and try and keep dumping in coolant, all with both heaters at full hot temp. dumb question but all this testing is with the system in manual not auto correct?

its either a blocked core, air in the system, or air mix servos not moving (but not likely since no heat in front or rear). have you checked every available fuse for the HVAC system?

 

[2001LC]

Welcome to mud!

I'm guessing this LX was sold, because of this very issue. What did Lexus and Toyota service history reveal?

- new thermostat Did you confirm in tech stream and with IR temp gun coolant temp? what was it?
- two coolant flushes, confirmed no air in the system. How have you checked for air in system (detail)?
- new heater T's and heater core flush (a tip thanks to searching this forum) Any blockage or foreign matter?
- heater core inlet and outlet temps are within factory specs, so seems unlikely it's that Was this with fan on full? What were temps?
- new clutch (blower) fan What is this?

Has flow of coolant from engine to core (just before DS heater Tee) been checked?
Has flow of coolant from cores to engine (just after PS heater Tee) been checked?
Have servo door operation been confirmed?
Anything else not working? I mean anything. Say like OAT temp readout on center console,power antenna, a light, AC, anything?
Has windshield ever been replaced? There are always signs if replaced.

Not having heat come from neither front or rear, is a clue. It may indicate flow of coolant restricted.

 

[TheForger]

Does cleaning this help the AUTO function only?

Honestly I’m not 100% sure but I believe so. The sensor detects the cabin temp and when on AUTO it will automatically adjust the AC temp & fan speed accordingly to keep it within a specified range

 

[kruisinkid]

yes the room temp sensor is like the thermostat in your house. when your system is on auto, that is the sensor that tells the cooler or blower when to turn on and how high, temp, etc.

 

[KliersLC]

I'll be watching this closely to see what you come up with. I have the same symptoms in my daughter's rig, but I already know what the issue is....debris clogging the front and rear heater cores because a genius PO used crap coolant and/or tap water....

This is on my list of things to do as I really do not want to replace the heater core... Heater Core Flushing - OWNED!

 

[Dunnik]

Welcome to mud!

I'm guessing this LX was sold, because of this very issue. What did Lexus and Toyota service history reveal?

- new thermostat Did you confirm in tech stream and with IR temp gun coolant temp? what was it?
- two coolant flushes, confirmed no air in the system. How have you checked for air in system (detail)?
- new heater T's and heater core flush (a tip thanks to searching this forum) Any blockage or foreign matter?
- heater core inlet and outlet temps are within factory specs, so seems unlikely it's that Was this with fan on full? What were temps?
- new clutch (blower) fan What is this?

Has flow of coolant from engine to core (just before DS heater Tee) been checked?
Has flow of coolant from cores to engine (just after PS heater Tee) been checked?
Have servo door operation been confirmed?
Anything else not working? I mean anything. Say like OAT temp readout on center console,power antenna, a light, AC, anything?
Has windshield ever been replaced? There are always signs if replaced.

Not having heat come from neither front or rear, is a clue. It may indicate flow of coolant restricted.

Thanks for the replies, will try to address:

- service history showed no work on the HVAC system or any associated complaints

- as noted, did not perform the work myself, it was done at Lexus Downtown in Toronto. The first thing they did was replace the t-stat, when no result, they said the first t-stat was actually a bad part; replaced with a new t-stat confirmed to be working, with no result. Was not told coolant temp.

- they've replaced the coolant entirely 3 times now, to no effect, each time running the system to eliminate any air; they seem sure there is no air in the system

- no reports of any foreign matter or blockage flushed out of the core

- assume tested with fan on full, was told temps at the intake and outlet were within 5 degrees C, which, I'm told, is within factory specs

- the fan that blows the, in this case, heated fluid in the core into the cabin?

- everything - other than a blown telescoping steering wheel motor - works

- unknown if coolant flow has been checked in these areas

- windshield is OEM glass, non-IR

- no difference whatsoever between any settings, auto/manual, direction, front/rear

To clarify, the system is capable of producing heat. When it was returned to me last night by their valet service, heat blew nice and hot. This morning, however, after sitting all night, back to "normal". It's very intermittent: this morning after nearly reaching operating temp it was blowing warm-ish air, but after a few seconds, it went to cold. As noted in the OP, I've seen the system take 40 minutes to finally start producing heat.

I've been avoiding driving the truck for long periods but there's a warming spell coming up this weekend, going to drive the truck more thoroughly to see if there's any kind of pattern, or if things get better or worse.