2017 F150 Supercrew 6.5' Bed, 5.0 V8 6 Speed, 4x4, XLT (XTR) model with manual climate control and heated seats, 50,000 miles

Multiple issues popping up after not driving truck for the summer - Ford F150 Forum - Community of Ford Truck Fans

So I am starting a new thread for this as the previous one I posted I was having multiple issues. Previous thread is linked above if you want to read what all was discussed. Now my main is that my engine fan will only run on high. It will not always fun, but if it does turn on it is on high and stays on for quite awhile. Here is an example of what happens. I started it up and the fans did not run at all. I drove into town (about 15 minutes), and the fans never came on. I left all my heat/ac off for the drive. I stopped and filled up with gas. Then when I restarted the engine the fans started immediately, turned on in high and stayed on for the remaining 10 minutes into work (all heat and ac still off). Ambient air temps were around 35 degrees this morning. Average highway and city driving, definitely not working the engine hard.

The air temps have been cold the last few weeks, I have not been using A/C or my max defrost, so I don't believe the AC has been running at all. Yesterday I ran some tests with forscan and got the following information.

CHT is 3.42 V (on another post someone said this equates to about 212 F), ECT is about 200 F, and AC Pressure is around 300 psi (guessing this is the issue).

Not sure if the AC pressure sensor is bad or possibly the expansion valve. Is it normal for the AC pressure to read high even if the AC is not on?

Using forscan this morning I saw that my engine fans would come on high at about 165 deg F. Also, my LFC and HFC come on at the same time, not sure if this is normal or not either?

 

Update: If AC Pressure hits 330 PSI, high fan turns on, AC pressure drops down to 290 psi eventually, fan turns off. Repeat

 

Even if you don't have the A/C turned on, the climate system (including the manual one) monitors cabin humidity. If the humidity is too high, the A/C may run (ambient air temperature must be above 32°F and evaporator temperature must be above 33.8°F) to dehumidify the airflow through the system. All airflow from the blower passes through the A/C evaporator core first. Temperature blending is controlled by the temperature door which controls how much air passes over the heater core.

 

Air temp has been below 30 all day today, so AC shouldn’t be running. So does it make sense that my AC pressure is so high? Any thoughts on what would be causing that other than a bad sensor? Also, I live in a very dry, non-humid area.

 

The A/C pressure sensor is easily removed and replaced. Change it out to eliminate that as a cause.

Even though you may live in a non-humid area, the air you and your passengers exhale contributes to cabin humidity. Footwear can easily transfer moisture into the cabin from ice, snow, or rain.

 

Ok got it. But still, the outside air temp was around 20 all morning, so I still feel like the AC definitely shouldn’t have been on. Is the AC pressure sensor the same has the AC pressure switch?

 

The AC will run intermittently anytime when a defrost mode is set on climate controls to dry out the air in the cabin to prevent fogging up the windshield.

 

Thank you for the info! Even if I have all climate controls off though (completely powered off) the fan will still turn on high. Also happens if heater is on and no defrost modes are selected.

 

Check the fan relays

 

I’ve checked. They all seem fan. I’ve switched them around with other ones that are the same and nothing else has stopped working.