Front defroster blowing cold on the Driver side

[Rick U]

This morning I had to defrost my windshield for the first time in months. Only the passenger side started clearing up so I put my hand up there and noticed the driver side was blowing cold air. The right side was blowing heated air. Is it possibly a setting on the dash? There must be a gate or valve that diverts the heated air, right?

2015 Limited

 

[Drizzie]

Both driver and passenger settings the same? Limited will have dual zone control.

 

[Rick U]

Yes it must have something to do with the dual zone. When I turn on the defroster it should override the dual zone and automatic right?

 

[rigtec]

This morning I had to defrost my windshield for the first time in months. Only the passenger side started clearing up so I put my hand up there and noticed the driver side was blowing cold air. The right side was blowing heated air. Is it possibly a setting on the dash? There must be a gate or valve that diverts the heated air, right?

2015 Limited

Hi Rick,

There are a few things that could cause the air on one side to be cold and the other, hot. First I'll assume that you've already looked at the temp setting on the driver-side! Okay, then there are three fuses under the hood that you'll need to look at... PTC-1 50A, PTC-2 30A, AND PTC-3 30A. These are all electric heaters to assist in getting the (DAT) discharge air temperature to rise quickly while the engine is still cold. If you've checked these three fuses and they're good, look in the driver-side junction/fusebox and see the A/C Fuse 7.5A. This fuse is hot-at-all-times and keeps the A/C Amplifier and related ECM's energized to store temporary history files and trouble codes for future reference.

Pull that 7.5 fuse out of it's slot and leave it out for a minimum of four hrs. This is what's commonly know as a MASTER RESET. It allows those corrupted/missing temporary files to be deleted, forcing the ECM to revert back to it's default (factory) settings. Chances are one of the mixed air damper doors has lost communication with it's assigned ECM, and so has failed in the cold air position... it may have been like that for some time now but you weren't using heat until recently so the trouble went unnoticed! If this doesn't resolve your trouble, post here again and I'll start putting up some schematic wiring diagrams to investigate into this further! "Let us know"

rig, 'Best'

 

[Rick U]

Thanks so much Rigtec, I'll check tonight after work.

 

[Rick U]

Hi Rick,

First I'll assume that you've already looked at the temp setting on the driver-side! ted, forcing the ECM to revert back to it's default (factory) settings. Chances are one of the mixed air damper doors has lost communication with it's assigned ECM, and so has failed in the cold air position... it may have been like that for some time now but you weren't using heat until recently so the trouble went unnoticed! If this doesn't resolve your trouble, post here again and I'll start putting up some schematic wiring diagrams to investigate into this further! "Let us know"

rig, 'Best'

I was able to get hot air from both sides by setting the driver side to 85 and disengaging the duel zone then pushing defrost. I had assumed defrost overrode everything and went to full heat on both sides until turned off. Ive been in Dual zone Toyota's and Lexus' for years and never seen the dual zone play a part in defrost. I'm almost out of warranty. Should I have it looked at or is that just how it works?

 

[rigtec]

I was able to get hot air from both sides by setting the driver side to 85 and disengaging the duel zone then pushing defrost. I had assumed defrost overrode everything and went to full heat on both sides until turned off. Ive been in Dual zone Toyota's and Lexus' for years and never seen the dual zone play a part in defrost. I'm almost out of warranty. Should I have it looked at or is that just how it works?

I would say to use it for a few days in cooler weather to determine if there's a problem with that system. I didn't realize you were using the 'Dual Zone' feature while defrosting and I don't know what temperature set point you had the Driver-side set for so it could've been doing exactly what you were asking it to do! Just keep an eye on it over the next few days and see if a problem exists!

rig, cheers!