[rklingsten]

Here in SE Michigan, we've barely been below freezing this winter until last week with the snowstorm...

But now that it's temporarily fairly cold, I notice that the 2005 SR5 with rear heat is really slow to warm the cabin. I've idled it for 20 minutes at 15 degrees outside, and getting in it's still cold inside. The heater is blowing warm air, but it seems like it just started to do so. So, slow heat .... thermostat or something else?

Also I noticed this slightly coarse to fine dark brown particulate across the dash. I thought it was from offroading in the mid fall and I cleaned it off a few weeks ago, but it's coming back again. So now I assume it must be coming up out of the defrost vents along the windshield. Maybe deteriorated foam gasket?

The heating and cooling just seems wimpy compared to my old 2001. On high, while it seems to be blowing and it's pretty loud on full blast, it doesn't seem very effective. Maybe a blockage somewhere in the ducts? I dunno, it's annoying.

 

[SilverSasquatch]

The heat for mine starts kicking in after maybe five minutes (system on AUTO). Be sure to check that the rear isn't set to a different temperature and the Sync is enabled up front. I found a doggie bowl and a bag of treats stuck under the front seat when I bought my car so it's easy for forgotten stuff to block those vents in the floor.

The particulates do sound like foam gasket material. They used that stuff everywhere from the circulation vent flaps to duct-to-dash sealing.

 

[rklingsten]

The heat for mine starts kicking in after maybe five minutes (system on AUTO). Be sure to check that the rear isn't set to a different temperature and the Sync is enabled up front. I found a doggie bowl and a bag of treats stuck under the front seat when I bought my car so it's easy for forgotten stuff to block those vents in the floor.

The particulates do sound like foam gasket material. They used that stuff everywhere from the circulation vent flaps to duct-to-dash sealing.

I guess I'll just put up with it until the weather warms up and then dig into the ducts and blower. I run a tight ship for "stuff" in the truck, so there's nothing blocking vents anywhere and the rear system is set to sync.

 

[BroHon]

Western MI here/2000 SR5 (No rear heat)
I removed my heater core hoses and did a Gentle reverse/forward flush with the garden hose. I also made sure the "Heater Valve" on the firewall was opening all the way up.
One thing that I did that seemed to help the most was burping the air out. I took it to a 45deg (edit: prob more like 30ish deg not 45!) hill, parked up on it at an angle putting the Rad cap at the highest point.
With the cap off I waited for the thermostat to open up. I then got under the hood and squeezed the upper hose, burped/revved/and added coolant, repeated as needed.
Having a funnel that fits tight in the rad will help to avoid spillage, it spits up a bit. I spent about 15 minutes doing that and was surprised how much air came out and coolant I added. I added Full strength due to the addition of water while flushing the core. If the cooling system has been opened up anywhere, air could be in there.
If you have an OBD2 reader your could see if the truck actually warms up in a timely manner too. That will tell you how well your thermostat is working.
Good luck

 

[MarkFC]

I had this problem with a different car and it was just plain low on coolant

 

[Andy4]

the fine brown/black particles coming from the vents may be the foam seals used to assemble sections of hvac ducts that have dry rotted.
i think there's a separate temperature valve in the rear hvac unit located at the rear passenger side near rear hatch.