No Heat

I have a no heat problem on my 2010 even though I have hot coolant circulating in/out of the core. What did you do?

 

If hot coolant is circulating through the core and you're getting non-hot air out, then the air isn't going through the core. That's a bankable deduction, as there just aren't other possibilities, assuming you're right about the coolant circulating.

The "air mix" damper is the one that controls the temperature by splitting how much air goes through the core and how much goes around it. Sounds like your air mix damper isn't moving from the "all air goes around the core" position.

That could be a problem with the damper or the servo or linkage that moves it, or it could be a problem with the cabin temperature sensor (if the A/C amplifier thinks you don't need any heat, it won't be giving you any). I seem to recall this isn't a terribly uncommon result if people have had the dash apart for some reason and neglected to plug the sensor back in.

You can use Techstream to view the reading of the temperature sensor, and also to waggle the air mix servo back and forth at will, and see what it's doing.

-Chap

 

OK, so I ran techstream and monitored the "Air Mix Servo Target Pulse" and "Air Mix Servo Actual Pulse". I also watched the room air temperature sensor on techstream (and ambient outside). Looks like the temperatures are accurate but the servo readings are odd. I can manually push the value from 0 to 255 on techstream, and reading follows except it only goes as high as 93 on both (stays at 256 on target briefly only). Not sure, but that may mean the motor can't move beyond position 93 and open door to the heater more. Could something be stuck in there? How do I get to that servo and blend door? I think I see the servo to the left of the blower motor. I have the glove compartment out and I can see the blower. I'm thinking or trying to remove servo and hand turn the door as a test. Any other options, or will that not work?

 

Ok, so I removed the vent tube to the passenger side foot area, and I can see the actuator and two radiator-like metal blocks inside. when I crank the heat, a screen pulled back and uncovered the bottom one. I'm guessing one is electric and the other coolant-fed. Still just getting a little heat coming out. Not sure what to try next.

 

Maybe if I get a chance I'll hook mine up and see what maximum reading it will hit. Maybe 93 is the normal limit.

... or, if it's slushy out, stay indoors and read the manual, I guess ...



Did you look for any of the diagrams in the manual for where the heater core is located in the case? It seems kind of high up, are you sure you're not seeing other bits through the opening you're looking in?



It might be interesting to measure (two thermistors, or an IR imager, or even just by hand) the temperatures of both the incoming and outgoing coolant elbows on the heater core while the engine is running, both while demanding minimum heat (fan low, mix door to cold) and maximum (mix door to hot, fan high).

In a normal car, you'd certainly expect the incoming elbow to be pretty hot, and the outgoing one to be almost equally hot if little to no heat is being extracted from the core. With the fan high and a lot of heat demanded, the return coolant elbow would probably be significantly cooler than the one coming in. A working car would be helpful to get a sense of the normal temperature drop. If it drops less than that, it would be likely that something's restricting the amount of air flowing through the core. If it drops more than normal, that would suggest a restriction in the coolant flow.

-Chap

 

Thanks Chap, this is really helping. I'll run the suggested test. I also watched engine temp and the coolant was plenty hot enough. If it is coolant circulation trouble and not the air flow, I'm thinking it is either:
1. Something blocking the coolant flow to core (including air). Bleeding air was easier in my 2006, but I thought that I had done this in the 2010...but perhaps I'm missing a step. There is a bleeder valve right in front of the heater core hoses, I kept that valve open until a pint of fluid came through it while filling with car off. Maybe that wasn't enough.
2. Pump is not circulating the coolant that path. How do I test this? I would think I would have an OBD error code in this case.

 

What we have is in essence a small hydronic heating system, and here's an article that gives the basic relationships among flow rate, fluid temperature, and heat output for those. I have Gen 1 and Gen 2 New Car Features manuals on paper, and in both of those generations the heater core max output was given as 5300 watts (or about 18,000 BTU per hour, to use the non-metric units in that hydronics article). I don't have a Gen 3 NCF manual open to look at, but we can probably assume the specs are pretty close; it's about the same size car. We know the incoming fluid (at full engine thermostat-opening temperature) should be around 95°C, or around 200°F, for Gen 3.

The New Car Features manual doesn't seem to give a figure for the coolant flow rate through the core. The formula from the article can be used to lay out some possibilities: if the flow is around 1 gallon per minute, then an output of 18,000 BTU/hr would correspond to a temperature drop around 36 Fahrenheit degrees, so the heater core's gozouta elbow should be around 164°F if the gozinta's getting fed 200°F.

If the flow rate's more like 2 GPM, then only an 18 degree drop would be needed for the same heat output, so the gozouta elbow temperature would be something more like 182°F if 200°F is coming in. And so on. Again, getting measurements on another car of the same model with a known-healthy heater would help to pin down what 'normal' is. From there, you could see what the measurements on your own car are telling you.

I'm using the density (61.3 lb/ft³) and specific heat (1 BTU/lb/°F) from the article's examples, which are probably for ordinary residential boiler water; if anybody knows the real values for SLLC, they could be plugged in to make the calculations a little tighter. Going by this, it looks like the corresponding numbers for 50% ethylene glycol (at 200°F) would be (61.3 ✕ 1.038) = 63.6 and 0.865 ... that would require slightly larger temperature drops to achieve the rated output, dropping from 200°F to 159°F at 1 GPM flow, or from 200°F to about 180°F at 2 GPM flow. Not hugely different from just using the numbers for water.

In Gen 3 it's the one water pump on the front of the engine that's responsible for circulating the coolant, even when the engine is stopped, and that pump is electric and variable speed, so the flow rate through the core won't be the same under all conditions. Still, it should be possible to learn something from how it behaves when maximum heat is requested.

-Chap

 

I rant he car for at least 30 min in maintenance mode. Here is what I learned:
-I did have a small leak on a front radiator hose, which explains the slow loss of coolant. I'm fixing that
-The two hoses to the heater core are hot to touch, not just warm.
-The engine temp rose to 205deg while idling but the radiator fan never engaged. What engine/coolant temperature does that fan engage at?
-I removed the servo to the mixer door and manually adjusted it. Worked full range and didn't really affect heat. I was getting wram, but not hot air when cranked full heat. I wonder it I have some blockage in the heater core itself now. Is it possible to purge a heater core or any sediment?
-I learned the pressurized coolant system int he 2010 is supposed to be self-burping of air. Not sure if that means I shouldn't have air in the core, but seems so.

 

Do you have anything you could use to measure the temperature of the two coolant hoses at the core? A key value is the amount of temperature drop from the supply to the return. It would quickly allow you to distinguish impaired airflow through the core (temp drop smaller than normal) from impaired coolant flow through the core (temp drop larger than normal).

"Normal" might need to be measured on a Prius with working heat.

-Chap

 

I have a contact thermal temperature gauge on my multimeter I could try. Also, I wish I had the schematic of the airflow in the heater assembly as it might help me know if I could reach in and detect something on top of the core blocking airflow. Any chance a sticky thermostat could cause this?

 

i don't agree, there is a burping valve in the system. it was eliminated in 2011+ IIRC.

 

OK, so I flushed the heater core (it was clean) and placed a thermal probe on the core in the dashboard unit, while things were running. It measured 180deg F, so plenty hot. Since the fan blows plenty hard, and the core is plenty hot, there must be some obstruction to the air passing through the core. I did put my hand into the passenger vent and felt warmth, but it wasn't what is should be if the air were diverted across the core entirely. I also manually rotated the mixer door after removing the servo, but that had little effect on the heat, though I did see a windowed door slide about 5 inches backwards above the other radiator thing, but beneath the core. I'm getting stumped...unless somehow there is debris blocking the air from the blower. I'll remove the blower and see if I can see through that side next.

 

I wish we had a detailed schematic or an opened-up HVAC unit mixer door from this car, so I could see how the mixer door works. I bought a inspection camera and am trying to probe around inside my unit form the passenger vent and it is awkward, but that door is the only remaining option that hasn't been eliminated, yet it moves and I worked moving it manually with the servo off. Seems like the door/window slides forward and blocks the heater core when at full cool, but its pulling back for warmth is the part I'm trying to figure out. Seems that there is a window and then another solid part.

 

Most useful drawing I seem able to find is this one, but it doesn't show how the actual damper looks, even though it shows where the servo is.



There is also a schematic, but it is so schematic it doesn't resemble the actual construction at all, and doesn't look like it would be much help.

-Chap

 

I am dealing with this exact issue starting yesterday out of the blue. It was particularly cold yesterday morning, so I set the heat on HI to defrost the window. But upon returning to my car to leave the windshield was still frozen and there was no heat. Dealer charged way to much to look at it and said it took him 3 hours to even look at the blender servo motor (it must be deep in the dash, or he just ripped me off). He said that the car got up to temperature fine and didn't get too hot, he seemed to think the issue was with the servo or housing specifically over the heater core or coolant issues. (I did have my coolant flushed maybe 1.5 years ago and have seen it drop due to what I assume could be bubbles in the system, but it's level is fine)

Either way, was there any resolution to any of your issues?

I can see the servo near the gas pedal moving when I adjust the temperature back and forth, So it appears to be working. I will look closer this weekend when I have time. I also just ordered a techstream device.
-HF

 

@HermanFelker, using Techstream (which any dealer certainly has), you can just plug in the diagnostic cable and tell the various servos to move and see if they do. The idea of the dealer doing 3 hours of disassembly just to find out what is or isn't happening is nuts.

Is it true your car is a 2008? This thread is about Gen 3 (2010-2015), so a couple things: 1) your heater isn't built like the picture in #34, and 2) it used a different servo design that is more prone to some electrical deterioration with age, easily fixed with a simple cleaning. This thread has more information on that, only for Gen 1. In your Gen 2, there is an inconveniently-placed computer under the dash making one of the servo mounting screws harder to access. yitznewton found a super-skinny offset screwdriver to solve that problem.

 

Yes, it is a 2008 (sorry for that) and I believe I have been 'Had' as the saying goes because I can see the servo without removing anything.... I wonder if I could get my money back if I fought... probably not. I was charged $530 for 3 hours and diagnostics and they quoted me about $3000 to fix the heat.. absolutely in-f****g-sane. My plan at this point is to force the blender door into the heat position until it warms up but we'll see when I actually get into the dash. I just bought a tiny webcam that I plan on snaking into the vents to see the Blender door before I even take anything apart.This car is at 250,000 miles and it's basically paid for itself in fuel savings so I'm not scared to DIY.

My Techstream Device is on my doorstep as we speak, so I will do some testing ASAP.
I can see that the servo yitznewton removed is functioning as I change temperature on the dash (but don't know the condition of the door it actually moves).

Thank you all for your support.

 

I turns out if I press the accelerator down hard and raise the RPMs the heat works! So I need to Bleed air out of my radiator.... How could the Dealership not see this!? I don't think they even looked at my car!! I wonder if I can get my $600 back..

 

I believe you meant “stealership”