Function of the Heater Core Temperature Sensor 4th Gen

[CM_Ram13]

I've been struggling getting heat in my '13 Ram 1500. Basically have checked and changed every single thing possible with the coolant and HVAC system besides change the radiator, thermostat, or water pump: they work just fine. I've always wondered the function of the heater core temp sensor (HCTS) though. Would this cause any temperature change in the cabin if it is not getting correct voltage, resistance, etc? Is there a fuse it is connected to? I've tried having it seated normally, unplugged, and keeping it plugged in while outside the HVAC housing - just hanging behind the glove box - with no difference in any scenario. Any help is appreciated.

 

[Jeepwalker]

IDK, you can look it up in the Serv manual. Go to the HVAC, heat, general description section. (Scroll to bottom of THIS pg, find your yr pdf manual, link takes ya to google drive, click download and 'ok' till it downloads - it works). I'm sure the answer is in there.

I have one question: Do you hear any gurgling of water/air in your heater core in the morning when you first start your truck ....and when you first take off? Just asking.

 

[Travelin Ram]

Check the temperature of the hoses feeding water into the heater core and back out. That will tell you if it’s receiving enough hot water, and if it’s dumping heat into the heater core the return water will be cooler.

Blend doors?

Is the AC compressor running when you’re trying to get heat?

Are the replacement parts OEM, or otherwise?

 

[mtnrider]

Have you replaced your heater core? A clogged heater core is the #1 cause of no or low heat in these trucks

 

[CM_Ram13]

IDK, you can look it up in the Serv manual. Go to the HVAC, heat, general description section. (Scroll to bottom of THIS pg, find your yr pdf manual, link takes ya to google drive, click download and 'ok' till it downloads - it works). I'm sure the answer is in there.

I have one question: Do you hear any gurgling of water/air in your heater core in the morning when you first start your truck ....and when you first take off? Just asking.

I’ve burped the system a bunch of times and have no air in the water pump, radiator or heater core. No sounds of any kind

 

[CM_Ram13]

Check the temperature of the hoses feeding water into the heater core and back out. That will tell you if it’s receiving enough hot water, and if it’s dumping heat into the heater core the return water will be cooler.

Blend doors?

Is the AC compressor running when you’re trying to get heat?

Are the replacement parts OEM, or otherwise?

I’ve pulled the dash at least 6 times, changed heater core, checked all blend doors and actuators. I tried disconnecting the ac compressor still with no luck. Everything was mopar oem replacements. Both hoses in and out of the heater core at firewall are burning hot.

 

[CM_Ram13]

Have you replaced your heater core? A clogged heater core is the #1 cause of no or low heat in these trucks

Yes changed it last winter and did a coolant/radiator flush at the same time. Seemed to help only a hair.

 

[RamDiver]

Both hoses in and out of the heater core at firewall are burning hot.

There should be a difference between the hose feeding the heater core and the return hose.
Can you use a laser pointer temperature gauge and measure the exact temperatures?

.

 

[Jeepwalker]

I’ve burped the system a bunch of times and have no air in the water pump, radiator or heater core. No sounds of any kind

Ok. That's good. A failing head gasket can sometimes simmer for years till it lets loose and screw up heating as well ...in some instances. You're not adding any coolant on a regular basis whatsoever, though...right? (spark plug color is all even?)

Just curious if the outside air/recirc damper closing all the way? If the outside air damper is broken or for whatever reason doesn't close ALL the way, there's not enough design-heat from the heater core to overcome all that cold outside air coming into the cabin. Unless it's 65 degrees outside. I know ...been through it. But you force-close a damaged outside air/recirc damper then suddenly it's toasty warm in the cabin like it should be.

I would read the factory service manual on the controls and heater box thoroughly. There are troubleshooting steps in there ..beyond the scatter-gun things you get on the internet. At this point you haven't found the issue, you know enough how it all works ...you need to *expertise* yourself on how it EXACTLY operates to zero in on your problem using a logical and organized troubleshooting approach. At least now you should know what works and what doesn't work inside your heater box. After all the time you've spent thus far, maybe investing time into reading it a long time ago would have gotten you there by now?? Not trying to be a jerk, just saying...you're close. But time to get serious now. Could be the controller, wiring, bad sensors???. Good luck. I'd like to hear what the final solution turned out to be.

 

[CM_Ram13]

There should be a difference between the hose feeding the heater core and the return hose.
Can you use a laser pointer temperature gauge and measure the exact temperatures?

.

I’d have to buy one. I can tell they’re close in temperature - not the exact same - but both hot enough I can’t hold either for more than 5-7 seconds each without burning my fingers

 

[CM_Ram13]

Ok. That's good. A failing head gasket can sometimes simmer for years till it lets loose and screw up heating as well ...in some instances. You're not adding any coolant on a regular basis whatsoever, though...right? (spark plug color is all even?)

Just curious if the outside air/recirc damper closing all the way? If the outside air damper is broken or for whatever reason doesn't close ALL the way, there's not enough design-heat from the heater core to overcome all that cold outside air coming into the cabin. Unless it's 65 degrees outside. I know ...been through it. But you force-close a damaged outside air/recirc damper then suddenly it's toasty warm in the cabin like it should be.

I would read the factory service manual on the controls and heater box thoroughly. There are troubleshooting steps in there ..beyond the scatter-gun things you get on the internet. At this point you haven't found the issue, you know enough how it all works ...you need to *expertise* yourself on how it EXACTLY operates to zero in on your problem using a logical and organized troubleshooting approach. At least now you should know what works and what doesn't work inside your heater box. After all the time you've spent thus far, maybe investing time into reading it a long time ago would have gotten you there by now?? Not trying to be a jerk, just saying...you're close. But time to get serious now. Could be the controller, wiring, bad sensors???. Good luck. I'd like to hear what the final solution turned out to be.

Haven’t had to fill coolant besides maybe 1/4 cup once a year. I figured that might have been from escaping through the radiator cap when it’s at operating temp.I hadn’t thought of the recirc door not fully closed, just open enough to cause an issue. I’ve also wondered if there’s another electrical connector somewhere that might not be getting a good enough ground. But I agree with you 100% in that I’ve been dealing with this and have waaay to much time into it. I’ll keep everyone updated as I dive deeper in.

 

[RamDiver]

I’d have to buy one. I can tell they’re close in temperature - not the exact same - but both hot enough I can’t hold either for more than 5-7 seconds each without burning my fingers

This is a good example of zeroing in on a fault.

Kinda sorta, almost, feels like, is just too objective. Get a proper gauge on there and identify the precise differences between the in & out temperatures.

I would expect the difference should be 5-7 degrees F or more with the fan cranked. If you can't see a significant temperature difference, this informs you that you have insufficient air volume passing across the heater core and should focus on the HVAC doors.

One of these temperature gauges is invaluable for troubleshooting automotive, electronics, and household drafts/insulation deficiencies.

They're less than $20 at Walmart or Costco.

https://www.walmart.com/c/kp/laser-thermometers

One question, have you ever tested the heat function with the recirc enabled?

.

 

[Jeepwalker]

I think he said both hoses were real hot... But yeah ...an IR temp gun is real cheap at H/F, Walmart, etc. Its a handy tool to have. You can check brake rotors or wheels for the possibility of a hanging caliper or pad. Lots of things. I learned that I can't eat soup if it's over 138*F. LOL...


EDIT: Be sure, if you buy one, to read the IR Temp gun manual on various material emissivity, and how to correctly use. Easy to trip a person up.

.

 

[RamDiver]

I think he said both hoses were real hot...

What does that mean? We're expecting to see a difference of 5 to 7 degrees F, how does real hot answer that question?

.

 

[crash68]

Basically have checked and changed every single thing possible with the coolant and HVAC system besides change the radiator, thermostat, or water pump: they work just fine

Is your truck an 8spd.(has shift knob)? The early models with the 8spd has a 3-way control valve that send the coolant to the transmission cooler when the cabin heat isn't needed. Those 3-way valves sometimes fail but don't always throw a CEL when the do.

 

[Jeepwalker]

What does that mean? We're expecting to see a difference of 5 to 7 degrees F, how does real hot answer that question?

I edited my response ...right away (probably before you saw the revised post)

I agree with you, it needs to be HOT. In fact, an engine temp of 160*F (say, a faulty t-stat) doesn't throw a whole lot of meaningful heat.

 

[CM_Ram13]

Is your truck an 8spd.(has shift knob)? The early models with the 8spd has a 3-way control valve that send the coolant to the transmission cooler when the cabin heat isn't needed. Those 3-way valves sometimes fail but don't always throw a CEL when the do.

No, it’s a regular shifter. I’ve checked into that but my truck doesn’t have one

 

[RamDiver]

I edited my response ...right away (probably before you saw the revised post)

I agree with you, it needs to be HOT. In fact, an engine temp of 160*F (say, a faulty t-stat) doesn't throw a whole lot of meaningful heat.

You were fast to tweak that, but I noticed the first version.

Correct me if I'm wrong but, we need to confirm that firstly, the temperature is sufficiently high and secondly, that there's a sufficient temperature drop across the heater core.

If the temperature drop is too small, that clearly shows there's not a sufficient volume of air passing across the coil.

If we do see a sufficient temperature drop across the heater core, then we need to determine where that exchanged heat is being diverted away from the vents.

I wonder if the laser-guided temperature gauge could also be used on the duct work behind/under the dash, tracing the ducts closest to the heater core and toward the vents.

.

 

[CM_Ram13]

I think he said both hoses were real hot... But yeah ...an IR temp gun is real cheap at H/F, Walmart, etc. Its a handy tool to have. You can check brake rotors or wheels for the possibility of a hanging caliper or pad. Lots of things. I learned that I can't eat soup if it's over 138*F. LOL...


EDIT: Be sure, if you buy one, to read the IR Temp gun manual on various material emissivity, and how to correctly use. Easy to trip a person up.

.

Basing the temp off of the top radiator hose after the thermostat opens. But I’ll pick one up and try after work

 

[RamDiver]

Lots of things. I learned that I can't eat soup if it's over 138*F. LOL... <<< LOL


EDIT: Be sure, if you buy one, to read the IR Temp gun manual on various material emissivity, and how to correctly use. Easy to trip a person up.

.

This is good advice ^^^^.

When I measure the heat exchanger pipes on my ground source heatpump, I applied a strip of black electrical tape on the copper pipes to take measurements.

The copper is too reflective, the temperatures measured are completely dependent on the angle and never consistent. The electrical tape seems to remedy that issue.

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