Your evaporator temp sensors says the refrigeration system is fine but it would be a good idea to check its veracity as they've been known to "lie".

The following is based on observations done yesterday on my '15 Explorer with DATC. I'd expect to see very much the same results from your Taurus but, since I don't have your car in front of me, be prepared for variations.

While monitoring the evap sensor specifically, cycle to vent only mode with both temperature controls set to their minimum. The evap temp sensor *should* read at or a bit above ambient inlet temperature if it's working properly. Outlet air at the center vents should likewise be at or a bit above above ambient temps. Varying the range of the left and right temp controls and confirm that you're able to adjust the outlet air temp from inlet to very hot. This will verify that the blend doors are working (or not).

One oddity that I did notice on mine was that the "percentage" of the commanded blend door position(s) ranged from 0 to 255 instead of actual "percentage". Probably a programming bug in Forscan in that it didn't scale the 8-bit number proportionally on an actual percentage basis. I also noted that several of the "status" readings displayed a "fault" status while the actuators were in transition. I also looked for but did not locate the PIDs for the blend door actuator feedback values. Don't know if they're not available to any scan tool on my vehicle, to Forscan specifically, or I just didn't identify them. I'll play with it a bit more today as I have time.

In the meantime, go ahead and check that evap sensor in vent.

 

Ambient air is currently 88
I have the AC running and evap temp reads 34, outlet air center vent is 63.
AC off, vent only settings as described above, evap temp reading 62 with the outlet air center vent 93.
Cycling blend doors to HOT results in 161 degrees outlet air center vent, with the evap temp remaining at 62 if that matters.
I also note that the blend door percentage range is 255 and the fault errors come and go and I see fresh air/recirc/error during transitions.

return to vent only settings and has been running for 5 minutes stationary...evap reads 64 with the center vent reading 101.

As I turn the AC back on I note that the compressor is cycling over and over again like it was before. the reason in PCM module showing for disable is high AC discharge pressure as it has been doing right along.

 

Sounds like the evap temp sensor is askew.

I monitored my Explorer for about 10 minutes. Whenever the A/C was turned off, the evap_temp PID slowly increased from around 40F to a few degrees over ambient as expected.

I'd point the finger at the sensor as the most likely suspect. They've been a subject of significant discussion and experimentation across multiple Fords built over the last decade or so. Bad news is that they only come with the whole evaporator and heater core case. You might want to see if one of those Fusion sensor or resistor hacks might work for you.

 

Do you have a link to the sensor hack you refer to?

what do you make of the high pressure? It seems like my gauges were showing that the pressure was a little bit high on both the low side and high side, in relation to ambient, and when the temperature increases, the compressor shuts down because of the high side pressure sensor reading… could that be related to the condenser sensor you’re talking about? Or is the pressure a separate issue?

 

Neither the gauges nor the ACP sensor indicated any issue with the high side pressure later on, only your initial screenshots showed that the PCM was pulling displacement from the compressor (EVACC_DERATE). I'd discount some of the the display in Forscan as that text may have not been specific to the actual reason. Just don't know.

Give good old Google a shot at finding you stuff regarding the sensor/resistor hack. I do not know if it's a viable alternative on your car though.

 

OK I found a bunch of videos and how twos for the evap temp sensor fix you’re referring to.
I finally found some resistors and they were delivered and I’m going to do the fix to see if it works, but my wire connectors behind the glove box are different than i see in the focus. In fact I think that my connectors are actually right underneath the glove box toward the right.
here is a simple instructable about this bypass that we are referring to. Note the connector and the wiring diagram.
https://www.instructables.com/Quick-...C-evap-sensor/
Can somebody post for me information regarding the connectors in the 2018 Ford Taurus limited with automatic temperature control? I’m looking to find out which connector, and which wires are the evapp temp sensor.

 

These should get you oriented. It looks like the sensor connector is just above the accelerator pedal facing the steering column.

I do have the complete set of service documentation for your car should anything else be needed.

 

I have been looking on the passenger side because that’s where all of these fixes are. Your info I think is showing me just where the temperature sensor wires come out of the box which I suppose I could cut, but it’s not the connector i was expecting … In the focus that wire comes over to the harness behind the glove box and goes into like a 16 pin connector. It appears that on the focus it’s wire number two and wire number four as an example. I was expecting to see a similar thing behind my glove box where there was a 16 pin connector and the evaporator wire came right over into it. Once I identified which wire in the connector was what I was looking for I was gonna splice in my resistor.
do you have a diagram of which wire goes into those connectors near my glove box?

 

The Focus' wiring is different. This is not a Focus so use the Taurus diagrams.

 

You are correct.
I was confused because I did not see what I expected. Thank you for the excellent information! I was able to locate the plug and then after disconnecting it checked the PID and I had an error evap temp sensor so I knew I had the right one. When I looked at the disconnected sensor via hvac forscan live i see -40 degrees. I inserted a 33k resistor into the two prongs of the connector and I read a steady 73°F. It was located exactly where described and I did not have to remove anything in order to access. here is an image

Evap temp sensor continuously shows 73. Compressor turns on and starts to cool. compressor disengages due to "High AC pressure" slowly it gets lower to a normal level and then re-engages and vents become cool...then disengages <1 min later due to High AC pressure as described above. Here is a picture of the gauges and the forscan.




not sure where to go from here....again not sure why the pressure skyrockets causing the disengagement. Pressure only skyrockets like this when the ambient is pretty warm out...say greater than 80ish.

 

Well, a 33K resistor makes the computer think the evaporator is about 72F so it keeps the compressor operating until it maxes out the high side pressure so it gets cycled off. I haven't looked into the logic behind the Fusion or Focus hacks other than just seeing that they existed.

What are your vent temps like with the compressor cycling this way?

 

It’s been cycling this way which is why I started the thread. So we have no change there when the ambient temperature is an excess of approximately 80°. I have not been able to test when ambient temperature is around say 73 because it’s warm out.
vent temps remain the same as above. Dropping to no lower than 64 and they go all the way up to Ambient. Then they come back down when the compressor engages then back up.
so even though the evap sensor was not accurate, giving it a steady temp of 73 has not changed the issue.

 

ok decided to do some after dinner testing...
Vehicle sat for probably 4 hours. I started it and let it run for a couple min then tapped max AC

Ambient 80 degrees, 51 degrees out the VENT!!!! This is the best I have seen. and it felt cold in the cabin after a few minutes.
So I let it run in the drive for 20 minutes. I was monitoring the data and enjoying the cold breeze.

AC continued to blow cold. Ambient air temp dropped to 73 over the same period and the vent temp dropped to 46.
Everything seemed to be running normally and the cabin was comfortable. So I decided to go for a drive...
As soon as I started driving the AC pressure skyrocketed and disabled the compressor. I continued to drive and watched the data. It would rise, disable, slowly regress to normal, and then rise again. vent temp was rising to near 65 degrees. The AC setting was on "auto" 65 degrees... I was wondering if maybe it was limiting because cabin was approaching the desired temp...so I lowered the setting to 60...
pressure continued to rise then fall while driving. All other data appeared to be the same as it was in the driveway except as the pressure increased, the EVACC% PID would drop from 100percent to eventually 0. Then as the pressure reached normal it would rise from 0 back towards 100 percent.
thinking that the cabin temp which had dropped to 64 was causing the computer to disable the compressor I went to max AC. Shortly thereafter, once pressure returned to normal range, compressor engaged and vent temp dropped back down to 49 degrees.



AC continued to run until I reached home and it was comfortable in the cabin.
At the end of testing ambient was in the 71-73 range, evap temp was a stead 73 thanks to the 33k resistor, vent was 49 degrees, and the cabin was a cool 64.

I dont know why it did not work like this in the afternoon when the ambient temp was a warm/hot 85-90. It obviously is working "better" at the warm/cool 70-78 ambient temps this evening. still I wonder why it was cutting out for high pressure this evening.

I will test again in the heat of the day tomorrow. Anything I should try or look for?

 

Well I did some testing at lunch...AC not working properly!
ambient temp is 88 degrees.
the AC starts up runs for about 15 seconds, then shuts off because of high pressure. 30 seconds later pressures fall and it starts back up...repeat
when it disables here is a photo of gauges and forscan:




when it starts running again here is what the gauges look like:


So I am getting 100 degrees out of the vents, then the AC engages and it might fall to 75 or so...then right back up.
It reacts the same in "auto" temp mode as it does in MAX AC mode.
reacts the same in driveway as it does on the road @40-50 mph

 

Regarding the cool morning testing: I've occasionally commented that a marginal system will appear to work normally in mild conditions but it will quickly fail when conditions become harsh. I'd be likely to apply this observation to your car and your testing.

I'm going to refer you to a very good article I came across in a professional periodical while researching your car's issue. Perhaps it will shed light on the subject.

Diagnosing the Ford variable displacement compressor | Vehicle Service Pros