Dual zone air con heating unevenly

[Aircheese]

Hi,

I have owned an is250 for 3 years and 1 year for is220d previously.

Recent months, my wife starts to complain about the air comes from her side is always lower than my side (driver side). I can confirm she is right.

Symptoms:

From a cold start until the temperature is up to a certain level, the vents are blowing the same temperature.

Once the car is up, the vent from her side starts to blow colder air than my side. (The aircon is in sync mode, same temperature setting for both zone. 21-23 degrees are our normal setting for winter)

Even in “dual zone mode” with her zone set up 2~3 degree than my side, her side is still lower than mine.

My thought:

I can confirm that the engine coolant is up to the right level. And the symptom dont really seems to relate to the coolant or blocking pipes.

Because the heating is always strong once the engine starts to warm up and it is same with my experience.

The only issue troubling me is the uneven heating.

I think it might be something wrong with the cabinet temperature sensors, my side or her side.

Do you know where are these temperature sensors located? or any experience with these kinds of issues?

[Mauler]

Will be interesting to see what people think of this as I'm sure this is the same on my IS250 - passenger side is deffo cooler than the driver's side when set to the same temp.

[Farqui]

Hey Martin, My GS has done this for a few years now and I oddly a recent regas of the AC helped and boosted the passenger output from stone cold (even when max heat selected on that side) to luke warm.

If you research online you'll see that the heater servos can play up - mine appear to all be working okay and I'm loathed to rip into them again as some are a right pain to refit into the heater guides.

Issues are also reported with the heater matrix's which have a design that can easily clog on one side of the vehicle, the passenger side for right hand drives. The design has both the feed and return pipes on the same side (drivers) so coolant flow across the matrix isn't even and the far side (passenger) can clog up.  I've flushed, soaked and back flushed my matrix numerous times and still find small black particles coming out, from where I can only speculate.  After all this, the passenger heat output has improved a little but the drivers side is really good now!  It's been a while since I did a flush, so I'll try and get another done when the weather improves.

Cabin temp sensors might be worth looking into if you use the Auto function but we don't and still have the issue.  Maybe I should test Auto again and see if there's any improvement?

To really investigate/fix either area any further I'm looking at taking the dash out but only when the ambient temps increase.  A new heater core/matrix can be sourced for just £46 from Rockauto + p&p, so whilst the dash is out I'm tempted to get one and replace mine anyway

Dave at Lex-Tek has seen a few older cars with clogged heater cores, he replaced one in an RX not long ago that felt much heavier than the replacement. 

I will also be keen to hear if other folks have fixed this issue.

Good luck.