HVAC Control Unit Calibration [FIXED]

I have a 2015 Ram 1500 with a complaint of no A/C. The customer says that he has, recently, had the Radio/Climate Control head unit replaced, an the A/C has not worked since. All button pushes are registered, and I can command the compressor "ON" with a scan tool. I have concluded that the pid for Evap Core Temp is the problem. The pid reads a temp of 20°, 3 volts (at ambient temperature). I checked the resistance of the sensor and it is in spec. @ 3.1K Ω. I am seeing a resistance specification range of 1.2K Ω - 20K Ω, in [strike]Alldata[/strike] ShopkeyPro. I can use a 100 Ω resistor (WAY lower than spec), in place of the sensor, and pull the voltage down to around 2.2 volts, with a temperature pid reading of 38°. This kicks the compressor on.


My question is: Is the Radio/Climate control head programmable? Will a calibration file correct this issue?

I should, also, clarify that the Radio/HVAC control head, and the A/C Heater module, are NOT the same component. The Radio/HVAC Control unit contains the buttons for the HVAC but, the signals are sent, via CAN bus, to the A/C Heater module. My pids are coming from the A/C Heater module. The temp sensor signal goes straight to the A/C Heater Module, not the Radio/HVAC control unit. ?Typing it out like that makes me think that I am barking up the wrong tree. My problem is in the A/C Heater Module. Not the, newly replaced, Radio/HVAC control head. ??Is it a coincidence? Or, is it related??

Where did you find the spec of 1.2K - 20K ohms for the evap temp sensor? I've been up and down SI, and can't find a range. All the diagnostics have you ohm wires, then replace the sensor if it's all good.

I'm getting the feeling that the A/C stopping and the Radio/HVAC head replacement is coincidental. :silly: And I think your reasoning with the Radio/HVAC head and the A/C Heater Module is right on. Google says a new evap sensor is $20-30? I'd take that gamble.

Tyler wrote: Where did you find the spec of 1.2K - 20K ohms for the evap temp sensor? I've been up and down SI, and can't find a range.

I found it on ShopkeyPro. Not, Alldata. (I have Alldata, ShopkeyPro, and Identifix...$450/month in SI :woohoo: )

Google says a new evap sensor is $20-30? I'd take that gamble.

Me, too. I, already, ordered it. I will have it, tomorrow. I don't think it will help, but for $20-$30, I'll eliminate the possibility.

As a final nail in the coffin, I back-probed the signal wire, at the A/C Heater module. With a DVOM, I monitored the voltage going into the A/C Heater Module. 1.66 volts going in, 3.02 volts displayed on scan tool. I shorted the signal, directly to ground. DVOM reading dropped to 0 volts, as expected. Scan tool displayed 2.2 volts. New module ordered.

Welp, I'm $30 lighter now. :silly:

I actually thought about shorting the signal to the ground last night! But by the time I got here this morning, you'd already figured it out.

Tyler wrote: Welp, I'm $30 lighter now. :silly:

:lol: No biggie. It'll be absorbed. :dry:

Btw: This morning, ambient temp resistance of original sensor was 3.4K Ω. New sensor was 3.2K Ω ( I might have that backwards.) I chalk it up to Preventive Maintenance.

Chad wrote: Btw: This morning, ambient temp resistance of original sensor was 3.4K Ω. New sensor was 3.2K Ω ( I might have that backwards.) I chalk it up to Preventive Maintenance.

You just saved yourself a warranty comeback.

On-topic-ish? Did you know there's a scan tool function to check A/C performance on these? A/C Cool Down Test. Kinda like the Toyota flow test?



I haven't seen enough of these to know if the cool down test is worth a damn or not. :silly:

New A/C Heater Module installed and all is well.

Tyler wrote: On-topic-ish? Did you know there's a scan tool function to check A/C performance on these? A/C Cool Down Test. Kinda like the Toyota flow test?

I haven't seen enough of these to know if the cool down test is worth a damn or not. :silly:

I did not know that. The Verus has many bidirectional tests but, I didn't see a performance test. I wonder if it can be activated without a scantool, by a button push sequence.