Function of the Heater Core Temperature Sensor 4th Gen

[RamDiver]

So I measured the temperature of the hoses for the heater core close to the block with the truck running after a 30 minute drive on rural highway.

The upper hose, output from the block measured between 154°F and 170°F.

The lower hose, return from heater core measured about 115°F to 135°F.

I also tested the hoses at the firewall and saw a difference between the two of about 10° or 20°F, IIRC.

I had the heater control on Auto, set to about 71°F.
The outside temperature was about 60°F.

I will try to perform the same tests tomorrow with the heat blasting in the cab
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[CM_Ram13]

After testing the hoses I got:

Top radiator hose 175°

Heater core in 152°

Heater core out 140°

Bottom radiator hose 88°

91° out of vents (used both digital and mechanical thermometer)

Outside air temp 64°

This is with thermostat open, truck running about 20 minutes, fan on high. Thermometer was about 2” away from all hoses when testing.

With fan off:
In hose 152°
Out hose 149°

So the temp differences in and out of core is not too far from the norm (+/- 12°), but both are way too low. I would’ve thought the coolant entering the radiator would’ve also been higher considering the temp gauge in the truck reads about 192° at idle.

 

[RamDiver]

I'm no expert but, you have an 8° delta from heater core in to out, you didn't indicate the temperature setting, we could guess it being set to max.

I have a delta of 10° to 20° with my heat control set to auto. If that is correct, it sounds like you have a shortage of air volume across the heater core.

I have some errands tomorrow morning, I'll make an effort to get more accurate readings at the firewall & vents and report my findings ASAP.

There are several members who are very familiar with the duct solenoid doors. Hopefully, one of them will make helpful suggestions.

YouTube also has videos on testing and replacing of same.

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[CM_Ram13]

I'm no expert but, you have an 8* delta from heater core in to out, you didn't indicate the temperature setting, we could guess it being set to max.

I have a delta of 10 to 20 with my heat control set to auto. If that is correct, it sounds like you have a shortage of air volume across the heater core.

I have some errands tomorrow morning, I'll make an effort to get more accurate readings at the firewall & vents and report my findings ASAP.

There are several members who are very familiar with the duct solenoid doors. Hopefully, one of them will make helpful suggestions.

YouTube also has videos on testing and replacing of same.

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I don’t have an actual temperature setting with numbers, just the knobs. Yes it was on full blast on highest temp setting.

I wasn’t thinking of taking different temps at firewall and close to block but the ones listed above were about 6” from the firewall.

Thank you for your continued input and information

 

[RamDiver]

I don’t have an actual temperature setting with numbers, just the knobs. Yes it was on full blast on highest temp setting.

I wasn’t thinking of taking different temps at firewall and close to block but the ones listed above were about 6” from the firewall.

Thank you for your continued input and information

No worries, I had guessed you had it maxed out, I'll just do the same when I test tomorrow. I'm expecting to see a bigger drop when the heat setting is maxed on my truck.

Measuring at the firewall probably makes more sense anyway because we want to see the drop across the heater core.

You're most welcome for the information and hopefully we'll get this figured out, sooner than later.

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[GTyankee]

just mumbling,
i think that i have the door positions right

the two hoses pass through the HVAC heater box & goes right back to the engine.

The hvac fan pushes Air through The Blend Door
If the Blend Door is working properly, it flips up or down.
If that Blend door is in the UP position, the air flow passes through the Heater box.
If the Blend Door is in the Down position, all of the Air flow blows over the Condenser & you get cold air out of the vents.

If you take the door off of lower glove compartment & look just to the left of the HVAC fan, you can see & watch the Blend Door Actuator arm move, just watch the little White thing, if it moves, the actuator itself is good.
If you unplug the electrical connection & remove the 2 screws from the actuator, the actuator can be be removed.

Once it is removed, take your thumb & finger & grab the White thing, turn it clockwise & counter Clockwise, you should feel a bit of weight, once the White thing stops, you may hear a thud, then turn it the other way & you should hear the same thud, that is the Blend door moving & stopping, as it should. If it works as it should, you can button everything back as it was originally.

A way to check amperage to the HVAC box, on the passenger side, there is a kick panel next to your Right foot.
Behind that panel is where the HVAC power connects to the rest of the harness.

Now, if the water flowing through the firewall is less than 190°F, your heater will never really get pleasantly warm in the late Fall or Winter.

In case any one wonders, the 3 way Heater valve is under the Air Filter box.
Just lift the whole Box out of the truck & set it aside.

 

[RamDiver]

just mumbling,
i think that i have the door positions right

the two hoses pass through the HVAC heater box & goes right back to the engine.

The hvac fan pushes Air through The Blend Door
If the Blend Door is working properly, it flips up or down.
If that Blend door is in the UP position, the air flow passes through the Heater box.
If the Blend Door is in the Down position, all of the Air flow blows over the Condenser & you get cold air out of the vents.

If you take the door off of lower glove compartment & look just to the left of the HVAC fan, you can see & watch the Blend Door Actuator arm move, just watch the little White thing, if it moves, the actuator itself is good.
If you unplug the electrical connection & remove the 2 screws from the actuator, the actuator can be be removed.

Once it is removed, take your thumb & finger & grab the White thing, turn it clockwise & counter Clockwise, you should feel a bit of weight, once the White thing stops, you may hear a thud, then turn it the other way & you should hear the same thud, that is the Blend door moving & stopping, as it should. If it works as it should, you can button everything back as it was originally.

A way to check amperage to the HVAC box, on the passenger side, there is a kick panel next to your Right foot.
Behind that panel is where the HVAC power connects to the rest of the harness.

Now, if the water flowing through the firewall is less than 190°F, your heater will never really get pleasantly warm in the late Fall or Winter.

In case any one wonders, the 3 way Heater valve is under the Air Filter box.
Just lift the whole Box out of the truck & set it aside.

Great info GT, thanks.

When I was testing heater core hose temperatures on my truck yesterday, I never saw 190°F.
Measuring the hose temperatures inches from the block, I was seeing about 151°F to 170°F, IIRC.
I plan to take measurements again later today and include more details on the settings.

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[RamDiver]

I found a service manual here at Ram Forum, compliments of Ian, @DILLIGAF.

https://www.ramforum.com/threads/ram-2013-1500-service-manual.181644/#post-2559320

If you search Blend Door, there are 244 entries.

Hopefully, the following pics are from the same manual I have saved on my PC. I've saved the pics and included page #s for reference.



page 12519



page 12514



page 12515


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[Jeepwalker]

If #5 flakes out (broken door hinge/actuator), it'll dump fresh (cold) air into the cabin the heater won't be able to overcome. Obviously #3 & 9 need to work in concert.

 

[Jeepwalker]

Fundamentally it's an amazingly sophistocated and compact system. It's the kind of AC system (in compact form) a contractor might install in a commercial building for $100k+. Complete with sophistocated electronic controls.

In the right mode(cooling/defrost), it'll do dehumidification: That is, air passes through the Evaporator coil first, which the coil temperature would be in the mid to high 30's* F range. Air passing through the AC coil will cool past it's dewpoint, which then dew condenses on the evaporator coil. The air *leaving* the coil now has much less moisture than when it entered, ...but will be much colder. Then the air stream passes through the heating coil which brings it back up to the temperature needed for passenger comfort. But because the temperature has increased it now has a much lower Relative Humidity. Since it would be in the recirculation mode (for cooling), much of that air (which was just dehumidified), passes through the same phases and comes out with even less humidity. That's just one mode, obviously. And the doors can modulate to blend accordingly. It wouldn't engage the cooling if heating-only was required.

Now it's a matter of figuring what "Isn't" working properly.

 

[CM_Ram13]

Yes, all those diagrams all look correct to me. When I pulled the hvac box out and apart last winter, I checked all the doors for proper function and reaching their open and closed maximums. I’ve toggled the first blend door behind the glove box, as well as taken the actuator off and moved it by hand. I notice a difference in temp when moving that first door, but as stated earlier it’s ice cold for AC or it’s sorta kinda warm on a cool day, or cold on a cold day. I’ve even blocked that door entirely from allowing air through the condenser by filling the duct with pieces of foam pipe and tying a string to the white knob of the blend door. All the other blend doors have no issue blowing to the correct areas. I’ll check the amperage to the hvac box by the foot panel but I’m unsure that would be the problem.

 

[mtnrider]

I know you have swapped it already, but this sure looks, smells, tastes, like a clogged heater core. I would at least try and back flush the heater core just to see?

 

[CM_Ram13]

I know you have swapped it already, but this sure looks, smells, tastes, like a clogged heater core. I would at least try and back flush the heater core just to see?

I did try that a couple weekends ago. I flushed it probably 6 times since I got the new core in last winter. Hasn’t bumped the temp up in the slightest

 

[CM_Ram13]

Is there any possibility whatsoever that it could be a low pressure from the water pump since the hose into the core is only 154° on a 64° day? Or are those completely normal temperatures to see?

 

[Wild one]

Is there any possibility whatsoever that it could be a low pressure from the water pump since the hose into the core is only 154° on a 64° day? Or are those completely normal temperatures to see?

Pull the heater hose off the pump and check to make sure the pumps outlet doesn't have a build up of crud inside it.Wouldn't be the first time i've seen the water pump outlet restricted on an older vehicle

 

[mtnrider]

Is there any possibility whatsoever that it could be a low pressure from the water pump since the hose into the core is only 154° on a 64° day? Or are those completely normal temperatures to see?

I would "think" that if the pump wasn't pumping like it should you would see an increase in your engine temp? Is it running about normal?


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[CM_Ram13]

Pull the heater hose off the pump and check to make sure the pumps outlet doesn't have a build up of crud inside it.Wouldn't be the first time i've seen the water pump outlet restricted on an older vehicle

I’ll pull that apart Saturday. That had been in the back of my mind wondering if there could be a blockage before the firewall

 

[CM_Ram13]

I would "think" that if the pump wasn't pumping like it should you would see an increase in your engine temp? Is it running about normal?


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According to temp gauge needle and instrument cluster (digital gauge), the engine temps are correct. Never had it run hot

 

[Jeepwalker]

I agree...might be time to check water flow.

Boring Story: When I was in college I had a car with terrible heat. Let's just say NO heat. In the winter in WI, you need some heat. We didn't have warm winters very often back then. It was an old school copper heater core in a 60's car. I tried a couple times, soaking the heater core with drain cleaning products (Lye ...Sodium Hydroxide) thinking I could de-lime it. Sometimes ya can, sometimes not. I was broke in college as I had to pay all my ..everything. The heater core with Lye and warm water inside would get SO hot you couldn't touch it! It would hiss and make noises there in a pan on the concrete. Obviously there was some lime and whatnot inside. I got 'maaaybee' a little more heat out of it, even after a couple treatments. Not enough if any, to matter.

Well, my roommate happened to work at the science lab & managed to get me some sulfuric acid (as I recall, that's what it was), it was the highest molar concentration that was possible. You handled it carefully and wore face protection. I repeated the same process using that ...and again, it got so F-ing hot on the ground, hissing away, you couldn't touch that heater core for quite a while! Then I rinsed it. BTW, the heater core was easy to remove back then, just remove a firewall plate.

Anyway, long story short, it still didn't produce much heat. Eventually I broke down and bought a new heater core and guess what? Instant heat! I repeated the same process years later on another vehicle. Point is, if/when the heater core gets plugged you can't always clean them out. Not saying this is the issue, but it could be. Heater core passages are *much smaller* these days than they used to be on those 60's cars.

 

[RamDiver]

Is there any possibility whatsoever that it could be a low pressure from the water pump since the hose into the core is only 154° on a 64° day? Or are those completely normal temperatures to see?

So, from the tests I performed just now, I'd say the issue or at least one of them, is that the coolant temperature 'in' to your heater core is questionable if 154°F was the hottest you saw, but there are lots of variables to consider.

Outside ambient temperature, ambient wind, heat radiating from the engine, where precisely we're pointing our gauges, etc.

Keep in mind that these temperatures we're reading are not exact and only a relative reference because we're attempting to measure the coolant temperature through a fat hose.

The temperatures I measured were all over the map and difficult to obtain simultaneous readings. I spent a considerable amount of time moving back & forth between the input and output hoses, doing my best to capture readings at close to the same time.

The outside ambient was 61°F.

The heater core input hose at the firewall was about 155°F but I did see it as high as 170°F.
The heater core output hose at the firewall was about 115°F.

This delta of about 40° on my truck compared to your 8°, makes me think your fault is primarily related to duct blending doors not closing sufficiently.

The inside temperature at the floor duct was about 165°F +/-. I did see 170°F once.
I was leaning into the footwell and reading on a piece of carpet next to the duct and sometimes aiming horizontally directly into the back of the duct.

The tests above were after about 30 minutes of driving while idling in the laneway with both front windows wide O. Heat setting & fan jacked.

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