I have a big favor to ask. Can someone with an '03 Dakota (or similar) measure the resistance across the pins of their evaporator temperature sensor? The sensor is easy to access, it's under the passenger-side dashboard just to the left of the blower motor resistor.



I have an ongoing problem where the A/C compressor engages intermittemtly, or sometimes not at all. The compressor is new (the previous one siezed) and the pressure is good. I had a mechanic run a diagnostic and he told me that the evap temperature sensor reported 32 degrees when the a/c wasn't running and evaporator clearly wasn't cold. He explained that this sensor is used to shut down the compressor to prevent the evaporator from freezing up, and a faulty sensor was preventing the compressor from starting up.

Sounds plausable, but I did some searching and this seems to be a very uncommon failure. In fact, there's hardly any info out there on evap temp sensors. And to complicate things this sensor is very hard to find. Mopar doesn't have it and there's no aftermarket replacement, so I'm likely going to pay a premium for it.

Before I find a replacement, I was hoping to use an ohm meter to verify that it's bad. It's a 2-pin sensor, and my understanding is that it's simply a thermistor resistor (resistance increases as temperature decreases). Mine measures about 2 to 4 MOhm at ambient temperature, which sounds extremely high (practically an open circuit, which could explain why the diagnostic reports 32 degrees). But I don't know what a typical value for this sensor should be, and perhaps my understanding of this sensor is all wrong.

If I can find out what the typical value is, then I can bypass the sensor with a resistor and see if the a/c operates consistently before I hunt down a replacement.

Thanks in advance for your help.

 

Can you get me the numbers on that label?

I looked at the diagram for that connector, and one of the pins goes to ground, and the other is the sensor signal.

If you measure the voltage on that pin, it's probably 5 volts, and is more than likely the same, whether it is connected or disconnected.

If a high resistance indicates low temperature, then zero resistance might turn the compressor on.

Or, get a hair dryer and heat the sensor up a little and see if the resistance changes.

If not, it's bad.

 

http://delphi.com/manufacturers/auto...rs/cc/evaptemp

 

Friar - thanks for your reply. The number printed on the label doesn't seem to cross-reference to anything, but I found out from my local Dodge dealer that the Mopar part number is 05061064AA. They did not have one in stock, but I ended up ordering one and I should have it here in a few days.

I tried bypassing it with a few different resister values with no luck, but perhaps I just didn't try a low enough value. I didn't try shorting it because I wasn't certain that I knew what I was doing. At this point I'm just going to wait for the replacement sensor to arrive.

One other thing I discovered is that when the compressor does not turn on (or when it cycles on and off continuously), the computer is telling it to do that. I can tell by feeling for the A/C relay to click. Whenever I feel the relay click the compressor turns on as expected. So this indicates that the problem is not an in-series sensor (such as pressure) or flakey wiring in the compressor circuit. The problem seems to be that the computer for whatever reason is not actuating the relay, which could be the result of a faulty reading on this evap sensor. I'm keeping my fingers crossed.

 

I finally received the new evap temp sensor (Mopar 05061064AA) and my A/C works great again!

In case anyone suspects that they have a bad evap temp sensor, you can check the resistance across the leads. My good sensor measured about 3.4 kOhm at ambient temperature (it was probably around 80 degrees at the time, give or take). My bad sensor gave me very high readings in the MOhm range.

For someone else trooubleshooting this, I suspect that you could bypass the sensor with the correct resistor value and make the A/C compressor turn on. I tried to do that, but in hindsight the values I was using were too large and the computer was interpreting that as a very low evap temp so it shut down the coompressor.

Hope this helps someone.

 

Good Afternoon Everyone
I know this post has been slowed down and not posted on since 2016 But
We ran into this issue today with not bring able to find a part and Dakotas aren't easy to come by around here
and the Dakota we had was a 2004 but the Evap temp sensor was no good.
We made multiple attempts to get this problem resolved and every angle we hit didn't do what we needed it too
one thing I did not see in this post was other vehicles that have the same sensor. We tried a few
but we got lucky so incase anyone runs into this issue and isn't able to get this part a 1999 Sebring WILL work
and those are everywhere in the junkyards.
We just wanted to take a moment and spread some information that may help someone in the future with this issue.

Must Love and thank you for all the information you did help with!
Hopefully we help someone with our information

Delta Service's & Repair
Port Charlotte, FL

 

Ooo, Good info! Thank You.