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Heater blowing half cold half hot? (fix on page 4)

147K views 63 replies 17 participants last post by  MacEwen 
#1 · (Edited by Moderator)
hey guys i searched around and didn't find anything about this... i told my mechanic and he said he never seen such a thing ,but hell have to take apart the dash to find the problem... I'm wondering if any of you guys experienced this before.

So my AC and heater worked prefect before up until a month ago i guess. before i knew it the left vent and the left center vent is blowing cold air... as cold as AC air. but the trip thing is the passenger side vents is blowing completely hot air like it normally would. i put the settings to full heat, high air, and aim face.

it first started in the far left vent then it moved to the center left vent. and on occasion the whole center two vents blow cold also. but the right vent remains hot.

i found a crack in the radiator recently and replaced it today. but it is still doing the same thing regardless. i heard that the vents could have gotten stuck??? and to fix it need to pull the whole dash out? i would really hope it wouldn't have to get down to that if not necessary... i don't even know who to bring it to to get a solid confirmation and repair on this...

if any of you guys have any input on this subject it will be greatly appreciated. thanks guys.
 
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#3 ·
#6 · (Edited)
Never mind. Good luck with your repair.
 
#9 ·
why? Why do you think it is servo fault?
IS300 and IS200 (which I have) does not have dual climate control, that means that the heater unit has only one servo and one air flap for temperature regulation.
That means - both, passenger and drivers side are controlled by the same servo and the same air flap.

sure you can check how your servos work by changing climate modes and looking at them, if they move, hold their position and if they dont make weird noises, there is no need changing them...

I am 99% sure, your problem (and mine was) is in heater core. problem is heater core gets clogged up or has an air trap, which means coolant is not circulating trough all core. since you changed your radiator, it could be air trap...

quite lot of IS200 owners in UK forums were suffering from this problem.
so - try to get out all the air out of system, if it doesnt help, try flushing you heater core.
 
#10 ·
I thought about the heater core being the problem too. Since he has hot air through the right side, i was suspecting not nessesarily the servo motor itself but maybe the damper that flaps inside moreless. To the OP, does both of your heater core lines get very hot? If the servo is doing the full range of motion then it's not that.
 
#11 ·
i just got the time to check on the servo and it seems to be mosving full range... im not 100% sure but its moving and not making any ticking or w/e just the gear moving sound and it seems to be a full motion no slips or stops. when i change the modes and the temp i see the same servo for both those controls. is that correct?

im not sure where the heater core lines are but ill go find out. and if it is clogged how do i go on from here? what do i do replace it? flush it? i found out when i replaced my radiator the previous owner put HELLA STOPLEAK into it. prolly to quick fix and sell to me... nothing else seems to be clogged. and the heat worked fine for like 50k miles before this happened...
 
#13 · (Edited)
If you look behind the glove box and to the left, there are two servo motors. The upper one controls the mode or air outlet while the lower one, which is kinda covered up by a small removable duct, is the air mix(responsible for hot/cold). It's rather difficult to see the lower servo's linkage, but it's there. Keep the fan setting not on auto but on a speed rather, and make sure that servo shifts fully. Also, if you look by your battery, you'll see the two heater core lines going through the firewall. They are also the black insulated lines behind those two servo motors and then they 90 into the plastic encased heater core. The evaporator and heater core are in the same unit. See if both the supply and return lines get warm and then hot as the engine gets hot. Just be extremely careful doing so as the temp gets as high as 220*F. As for a flush, if there was a leak stop induced into the system, then I would have it flushed either by drain and refill or at a shop where they can do same but using a machine and higher pressures(such as a Wynn's machine).


I have the exact same problem but haven't had time to figure out a solution. i bought the car salvage from a front end hit and put a new rad in so im thinking it might have a air pocket in it as well or possibly low on fluid might cause it to not push fluid all the way through the core. but im going to subscribe and hopefully get some time this weekend to test some theories.
You very well could have air pockets in the system if it wasn't bled properly. Just jack up the front end or park on a steep hill. Allow the car to come up to operating temp, gently squeezing the lower but especially the top radiator hose. Make sure to keep the reservoir half full and to run the climate control on max hot but low fan setting. You may notice some gurgling behind the center console when the car is cold if there is air pockets. Remember the only thing that should go into the coolant system is Toyota Red and distilled water, unless the system is completely flushed, filled up with distilled water only, ran for a few days, and then a different type of coolant can then be used. Never use tap water and it's always a good idea to monitor the level of coolant when the car is completely cold(mainly if you think the engine is consuming coolant).
 
#12 ·
I have the exact same problem but haven't had time to figure out a solution. i bought the car salvage from a front end hit and put a new rad in so im thinking it might have a air pocket in it as well or possibly low on fluid might cause it to not push fluid all the way through the core. but im going to subscribe and hopefully get some time this weekend to test some theories.
 
#14 ·
okay jason... i drove home from work today and after i parked i took off the glove box and i reached back to feel the heater core lines... both of them seems to be hot i put my finger tip on them one by one and they seem to give me the burning skin effect haha... so i dont know what this could be now... i also reversed back into my drive way so now its inclined and hopefully any air will come out of it over night? maybe? if none of this works then i dont know what to do from there...
 
#15 ·
Well, I am stumped.

The only thing I can possibly think of since your passengerside is hot and driverside is cold is either there is a heater core blockage(even though both the inlet and outlet lines are hot) OR the damper controlled by the air mix servo isn't shifting right causing cooler air to be forced downstream to the end vents. Below is a very similar thread in which all of the same aspects were covered like in this thread. I also remember trying to help another member awhile back with the same issue, but no success. One thing I'm not sure of is how the heated core is routed. I would think it would be one series looped pipe but it may very well be a parallel grid and maybe there is blockage. I wonder what the temperature feels like for the driverside rear seat because that comes off the same ducting and is branched off at the same spot.(see below).

http://my.is/forums/f115/weird-heat-problem-421185/

2002 IS300: OEM Electrical (HEATING & A/C - CONTROL & AIR DUCT) Replacement Parts
 
#16 ·
The problem IS in your heater core! I tell you!
The reason why both of your heater core hoses were very hot it is because IS300 and IS200 does not have a bypass valve or anything else that controls coolant flow in the core. heater core is directly connected to primary (or small) cooling circuit on the engine and it is hot all times, even when your ac is set to max cold....
I made a drawing for you so you can see whats happening with your heater core

 
#18 · (Edited)
I guess I'll join the list because I have the same problem. Both of my heater core hoses are hot and I bled my cooling system. I don't hear the gurgling sound when the car is cold, so I'm guessing there aren't any air pockets in the system. Im just going to bite the bullet and change the heater core. I do notice on long drives the driver will get warmer, but the passenger is still hotter.
 
#19 ·
I guess I'll join the list because I have the same problem. Both of my heater core hoses are hot and I bled my cooling system. I don't hear the gurgling sound when the car is cold, so I'm guessing there is no air pockets in the system. I was reading another thread on here and a member stated that he changed the whole blower unit to fix the problem. He said something about an air blend door. I'm going to look for the thread and post it.
If half of your vents are hot and the other half are cold when the climate control is set on max hot, then as lex2oo mentioned, your heater core has some blockage. It wouldn't be the blower because that only makes airflow, it doesn't change the temperatures. I may have been "that guy" that mentioned about the air mix damper possibly causing the poor temperature regulation(only because we ran out of options), but after seeing that the heater core is of a parallel design, that only seems to make sense it is the heater core. It may be worth it to flush the system several times using distilled water only to see if the blockages can be freed up. I would also drain the block when you do the flushes. That would be the last hope that i can think of before replacement. Most auto repair shops offer a coolant system flush, which may be another option.
 
#20 ·
Thanks Jason. I actually edited my post, I didn't see the post with the diagram of heater core. It makes a lot of sense. I'm going to try and flush it again but Im leaning towards the heater core. My question is, does the whole dash have to be removed in order to replace the heater core?
 
#25 ·
there is a SH*T load of work that has to be done to get that sucker out... even with whole dash out the core is barely visible. Whole heater unit has to be removed, and AC must be discharged... this is how it looks like:

When I had my dash removed I disconnected those two aluminum hoses in the place where they enter the core itself. they are pressed in the core and not ment to be removed, so it is quite risky, I would not recomend to do it, but I guess I got lucky.
core pipes are easy to access from engine compartment, so if you have a gardening hose with good water pressure, you could do the work by yourself.

some use vinegar, some bleech, some citric acid and there are some chemicals specially made for radiator flushing. I dont know what works the best so do a search on that. and the idea is to flush the core, both directions with high pressure, then fill it with some chemical and leave for the night, after that, flush again... should help
 
#28 ·
So just as an update on mine i had it flushed by my friends shop cause i have no time with school and he said their was alot of dirt/grim crap in the system and that fixed it but i should drive it for 2 weeks and reflush it. I had heat for 2 days but guess it clogged again cause now the drivers side is cold again but not as cold as before but the pass side is hotter than before the original flush so it did do something. he reflushed it a second time and its a little better but still cool air i think im gonna try a chemical and flush it for a third time.
 
#29 ·
Are you flushing the system as a whole or are you flushing just the heater core? Just curious, I thought you can remove the flex line off the hard pipe right before the firewall. That way you can flush it backwards as well. Sounds like you're making good progress though.
 
#30 ·
Holy cow. What a pain. :(
 
#31 · (Edited)
I hear ya, definitely a whole weekend project and that's even if you have the tools/equipment to remove the core and recover the R134a. I know to remove the heater core, the whole dash needs torn apart, A/C refrigerant recovered, and whole assembly taken out. What I was suggesting to those who have this issue, why not open the lines shown in the pic below and stick a garden hose on both sides, giving it a backflush as well. Hell, I'd even hook my pressure washer up to it before having to rip the dash apart. It's definitely a lot easier and would be an epic simple fix verses replacing the core. Well, it's worth a shot IMO.

I have read many threads where a common cleaner, CLR, was used with great success. It is a mild acid that removes rust and scale. I've even read that oxyclean can help(not positive on our car though)

This is right near the firewall, where the heater core lines are.



here's the cleaner I've been reading about. Available at pretty much most household stores. You would want to use some pvc tubing to hook up to the outlet or inlet(depending on which way flushed), and drain it into a bucket. You don't want this stuff on your skin and all over the car, obviously. Fill the core up with that for a bit(I believe a diluted mix), and then make sure that it gets completely flushed out. Should do the trick if it's not severely clogged up.

 
#32 ·
I've used CLR to remove lime scale around the house. That shit is awesome! My real estate agent turns us on to it, and you know they practically clean houses for a living ...
 
#35 ·
If the passenger side is hot and working good then you probably suffer from the same problem as others have had, a partially clogged heater core. Please read the last two pages as it shows you why and what you can do to try to fix this(flush core).

Not sure about the whistling noise. Does it come through the vents or change whenever you change the various functions on the AC control console?
 
#38 ·
im in a mess too..i wish i could have solved my problem within a few weeks but no.........
i recently had this problem with my altezza 1999 with 3 s ge engine. it was blowing cold on left side so after taking it apart i need a water pump and a heater matrix. before i buy one does anybody know if a uk lexus heater matrix is the same or do i need a altezza one. thanks a lot
 
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