Only 1 vent blows warm air

[cjk712]

So I live in Los Angeles and I've had my 2013 BRZ limited with the auto heater control for a few months now.

Haven't really had a reason to use my heat since it is very warm here. Last week I went on a long road trip to Death Valley and other national parks, and it was very cold so for the first time I turned my heater on.

Unfortunately with the heater turned to MAX only the left most driver side had any heat blowing at all, with the other ones blowing cold air. AC works on all vents so it shouldn't be the fan. Also I checked the coolant levels and they were more than adequate. I dont it wasn't the thermostat, since there were no weird engine temperature issues during that whole road trip. I'm at my wits end to what the problem is here. Any help is appreciated.

[Stang70Fastback]

Dumb question, but are the left and right temperature control knobs set to the same temperature? Dual zone climate control sometimes catches people off guard who aren't used to it. The button labeled "Dual" will lock the left and right temperatures back together if you accidentally touched the passenger side control knob, which "de-syncs" them.

[cjk712]

Yes both maxxed out and only a little puff of warm from the left most vent.

[Stang70Fastback]

Try manually overriding the blower to the slowest speed (just to quiet things down), then change from hot to cold. You may want to get your head in the footwell area while you do that. I would imagine you SHOULD hear the blend door moving (or at least hear the motor whirring) when you do this. If you don't, perhaps something is mechanically stuck? That's as far as my rather limited experience with HVAC troubleshooting takes me, lol.

[cjk712]

hmm interesting, I will try that. Sounds a whole lot better than a heater core issue, Thanks!

[RZNT4R]

I see this type of issue, but with AC, quite often on dual zone systems.

When the system doesn't have enough refrigerant, it'll often boil as soon as it enters the evaporator, cooling only a small part of it. Depending on where the split for the dual zone is, that usually means just one side gets AC while the other does not.

We are dealing with heat in your case, but as a dual zone system, that same principle may still apply. You may have a low coolant level, and just one section of the heater core is actually getting hot. Looking at a diagram of the HVAC unit, the pipes enter the heater core from the left and circulate vertically. Right here and now I'm not certain if it flows up or down in the core, but each would mean different things: If it flows down, it could be low coolant or clogged heater on the right side. If it flows up, then a low coolant situation would be unlikely.

[cjk712]

My coolant levels have been consistently high, before and after the engine is warm so I don't think its a low coolant level. What do you mean by clogged heater though, does the heater core serve each side of the hvac system independently? how would you check for a clogged heater? Thanks for the detailed reply to my original question!

[RZNT4R]

Usually, there is a plastic divider in the middle splitting the air for either side, independent movable flaps are used to set the temperature for either side. A heater will usually clog on the side that's far from the inlet/outlet, in this case, it'd clog on the right side.

You can check for this by fully warming up the car, then setting the fan on high to max heat, and touching the heater hoses. On a heater that flows well, the inlet hose will be VERY hot (engine temp), and the heater outlet hose will still be very hot, uncomfortably so. If the flow is restricted, the outlet hose will cool down to comfortably warm.