FFH 2010 A/C Issues - Evap Temp Sensor?

[Evtx]

Hi Folks,

 

First off, I am a novice when it comes to cars, but I am trying to learn.  Sorry if I use any incorrect terminology, and thanks in advance to anyone that can help.

 

A few weeks ago, I noticed the A/C stopped working as well as it normally did.  It blows moderately cool (65°-70° F) on the driver side front vents intermittently. The air coming out seems to change temperature every few minutes.  I think it might have do do with the compressor cycling, but I don't actually know how to tell except the car makes different sounds and then air blows colder for a while.  On the passenger side, it seems to blow closer to 80° F consistently.  I thought it may be the blend door actuator, but when I look on the driver side, I can see the shaft (and some sort of valve/plate) move when I change the temperature setting.  I can see the shaft move on the passenger side to when I adjusted the temperature setting for that side.

 

I also have the OBD FORScan dongle.  With this I was able to to confirm the blend doors seem to function correctly.  The app shows them both move from 0%-100% when I adjust the settings (just found out I can do check this with the app today). I was also able to use the tutorial post in the forum to change the battery age and restore more normal Hybrid operations.

 

I read a contentious post about here with someone that has a similar situation.  For the person in that post, adding refrigerant seemed to fix it.  Of course, being a novice, I did not want to try anything that might make things worse, so I took it in to a local shop.  I paid about $130.00 for an A/C diagnostic and they said it was low on refrigerant.  I think the machine shows 1.1 and the sticker under the hood indicates 1.4 (sorry, not sure what unit).  So they filled it up to the recommended charge and I paid.  On the way out, he seemed to indicate the compressor may not be functioning correctly, and I could come back in a week if it was not working an apply part of the A/C diagnostic fee to the repair.

 

Having driven the car around a bit, it does not seem the service did anything at all.    I noticed that you can read the HVAC Evap Temp Sensor with FORScan, and I figured I might as well see what it says.  When I checked it after arriving home from the mechanic, it was reading 1°-4° C.  It is currently around 97° F outside.  Does that mean the sensor is faulty?  It is not likely it could have frozen up in the time the mechanic was checking it and my drive home.  I saw a YouTube video where the sensor was replaced.  After replacement, the sensor was reading the ambient 65° F, so it appears mine is way off the mark. 

 

This brings me to my main question.  Does it make sense that the sensor is what is causing my A/C issues?  If so, I think I have the choice of splicing a resistor or pulling the dash and replacing the sensor.  As a complete novice, I am unsure about the skill required for the dash pull.  It looks a little intimidating.

 

Of course if it is a problem with the compressor, I think all that might be a waste of time.  Does anyone know if there is a way to check out the compressor using FORScan?

 

Thanks to anyone that has any advice.

[eGuru]

Replacing the evap temperature sensor with a resistor is ridiculous as the evaporator will then definitely freeze up at times.

If you are still getting airflow then the evap cool is not freezing up. A sensor reading just above freezing is perfect.

 

 

[Evtx]

Hi eGuru,

 

To be clear, the sensor is reading 1-4° C before the air conditioner has turned on when it is nearly 90° F outside. 

 

I looked around in FORScan some more.  It appears the compressor is not even turning on.  Could these readings on the evap sensor prevent the compressor from activating?

[eGuru]

10 hours ago, Evtx said:

Hi eGuru,

 

To be clear, the sensor is reading 1-4° C before the air conditioner has turned on when it is nearly 90° F outside. 

 

I looked around in FORScan some more.  It appears the compressor is not even turning on.  Could these readings on the evap sensor prevent the compressor from activating?

 

Thanks for the clarification. Yes those readings could prevent the compressor from turning on. So either the sensor is bad or the HVAC controller is not converting the resistance value correctly. Usually when the sensor itself goes bad, the controller reports some large negative value.

 

 

pull the black connector off the the HVAC controller and measure the resistance from pin 6 (might be a VT-BN wire) to ground.

 

 

 

[Evtx]

Sorry for the delay in updates.

 

When I checked the sensor reading again, it was showing something like -40° C. 

 

I wired in a resistor like the tutorial, and now they A/C works well.  I may pull the dash in the future and replace the temp sensor properly, but the cheap fix saved my a big headache this summer.

 

 

[nationalwheel1]

Boy this is a late reply. Your evap temp sensor is bad.   Temp of -40 is like a default reading for a bad unit.  In my case the evap temp sensor was reading about 15 - 20 off the actual ambient temp.  Example,  Forscan showed ambient temp of 70,  evap sensor showing 50.  I tested over several mornings before startup.  So what that was doing was shutting down the ac compressor well before the car was sufficiently cooled.. vent temp 60 - evap core around 33 - 49.  Took me a while to diagnose it using forscan.  I replaced the sensor,  cost 50 bucks,  myself.  Ice cold air again.  Dealer was in the 800 - 900 dollar range.  I have all service manuals,  however I used a video on youtube for directions.  Very good I might add.  Took me about six hours,  I'm pretty slow.  I believe now I could have the dash off less then one hour if needed again.  I pulled the dash completely back in order to get that pesky sensor out.  The hardest part is removing and replacing that metal clip that holds the pillar on.