Code 71 - a/c evap temp low - where is this sensor that is causing this?
Melting Slicks
Joined: Feb 2003
Posts: 2,685
Likes: 814
From: Saskatoon Sask.
Drifting
Joined: Jul 2004
Posts: 1,358
Likes: 291
From: MA
The signal output on mine was close to 0vdc since the sensor circuit had a short.
My AC was affected with erratic compressor operation. And as I said above the low 3.6vdc reference voltage caused an ABS/Traction control light to come on with an error code.
This sensor is a three wire pressure sensor it has three terminals; a ground, 5vdc reference voltage derived from the computer, and the output signal going back to the computer.
It was a bitch to figure out because I was trouble shooting the ABS/Traction light error not so much the AC problem.
Last edited by grandspt; May 18, 2026 at 11:50 AM.
Racer
Joined: Feb 2010
Posts: 371
Likes: 65
From: south wilmington il.
I have a suggestion - take it or leave it. You need to go on Youtube and educate yourself as to how the refrigeration cycle works.(watch REAL information, not Scottie Kilmer type) It is obvious by some of your statements that you don't understand it. I will help you on this but I have no intention of conducting another seminar on the basics of refrigeration. That is something you need to learn yourself and many of your questions will answer themselves. Last year about this time, I posted a thread extensively outlining how the cycle works. Go find it. An AC system is no different than a BBQ tank. Does your BBQ tank stop having pressure just because you quit cooking hot dogs? It is called "static pressure" and varies with the ambient temperature. That pressure will always be there whether you have the AC on or not. And no, the static pressure does not have any reflection on whether or not it has the proper charge.
Last edited by merc49; May 19, 2026 at 01:33 PM.
Melting Slicks
Joined: Feb 2003
Posts: 2,685
Likes: 814
From: Saskatoon Sask.
this guy wants to plug in a scanner on every problem there is. Wouldn't a knowledge of A/C systems and how to use the pressure gauges work just fine. Back before computers I think that's how we diagnosed problems. I have a 49 mercury with a 70's Sears A/C system that mounts under the dash and zero computer hook ups. Just curious if the modern systems accept old school diagnostics. I've fixed mine many times just by using guages and a multimeter for the electrical parts. Or am I just old and missing something.
