Howdy everyone.  First post.  I tried searching and couldn't find anything. We have a 2009 Forester and noticed now that the weather is getting cooler that the heater only blows hot air when the temp knob is turned all the way up to 85 on the dial.  Any less, like 80, and the air blows cool and warms a little, then cool and warms a little, and on and on and on.  The AC is great and the heater worked fine last year.  Standard oil changes and brake jobs is the only thing that's been done to it since last using the heater.  I'm an air cooled guy so I haven't a clue as to what could be going on in my wife's car, but I'd like to try and fix it.

Any ideas?

I have not worked on this type of problem, but you can download the FSM and check it out.

https://sl-i.net/FORUM/showthread.php?18087-Subaru-Factory-Service-Manuals- 

Extract the zip file to its own folder and to start, go here - 2009\BODY SECTION\HVAC SYSTEM AUTO A-C DIAGNOSTICS ACdiag 

There are several PDF files to look at for diagnostics. There are also some that tell you part locations like Ambient temp sensor, Sunload sensor, In-vehicle sensor and other parts.

I dunno what it is, but the car has a cabin air filter -a fresh one couldn't hurt and maybe give you a chance to check for rodent damage or loose wiring in the blower area....?

check radiator level - in the radiator, don't trust the overflow to reflect actual coolant volume.

Also look into the possibility that you have a leaking head gasket. 

Hopefully not, but if they’re the original HGs I’d be suspect about them. 

Cheers 

Bennie

2 hours ago, el_freddo said:

Also look into the possibility that you have a leaking head gasket. 

Hopefully not, but if they’re the original HGs I’d be suspect about them. 

Cheers 

Bennie

Thanks.  I hope not too, we had a main seal crap out on us.  Bought a new block and rebuilt the engine.  This was roughly 35, 000 miles ago.  I had them checked just in case about 20,000 miles ago by a local Subaru mechanic.

1 hour ago, PaulP said:

Thanks.  I hope not too, we had a main seal crap out on us.  Bought a new block and rebuilt the engine.  This was roughly 35, 000 miles ago.  I had them checked just in case about 20,000 miles ago by a local Subaru mechanic.

Should be fine then if heads were shaved and the HG replaced properly. 

Cheers 

Bennie