A/C RELATED ENGINE RPM RISE ON HOT DAYS

[jbwilli]

REF 2010 Ford Explorer Eddie Bauer 2WD AUTO STD V6. w DUAL AIR. From a dead COLD start (meaning engine has been sitting and all fluids, engine and transmission are at ambient temperature) and ONLY when outside temperature is above 90F, the following occurs on most occasions. Engine starts normal, AC selected on. Transmission in PARK. Immediately, I can tell the electric fan clutch has locked, as the fan noise of moving air is higher due to it moving a larger volume of air. Suddenly the engine RPM increase far above normal idle RPM (>1500rpm). Shortly, everything returns to normal and I shift into Drive and drive away at a normal low speed (say 30 mph). Sooner rather than later, the RPM rises far above what it should be for 30 mph, as though the transmission has been prompted to downshift into a lower gear. Then the fan clutch locks again. This repeats off and on for up to five minutes and then all returns to normal and will not repeat again until next cold start! The output A/C air is great...38 to 42 degrees F. Only occurs when A/C is on. COMMENTS? Thanks!

 

[RandomNerd2000]

I do have to comment that you only have a manual AC clutch, no wires going to it, it works off temperature of the air going through it and the engine bay temp.

 

[jbwilli]

My fan clutch has 4 wires going to it! I assume it engages via a 12 v supply in 2 of those wires and is commanded to ENGAGE dependent upon a signal from the ECM via some temp device. My Eddie Bauer has an external temp sensor (sends a signal to my dash giving the OAT). Does it also send an OAT temp signal to the ECM as well? This would explain how and when the fan clutch knows to lock up (engage) and my fan clutch may be working normal? My real concern is how does the transmission appear to drop into a lower gear than normal drive, as my rpms go way too high for the speed I am going, only when it is HOT outside and I have the A/C on and ONLY for a short time (5 to 15 minutes) after a COLD engine start? Thanks for your reply!

 

[jbwilli]

*** UPDATE *** This symptom went away from fall and now it is April 2019. The symptom returned today, but it is only 60 degrees outside today! For the first time after a 3 minute drive, the dash RED hi temp light illuminated while the dash temp gage remained at NORMAL mid range. The RED temp light displayed for about 15 seconds and the fan clutch engaged and the engine RPM went up to 3000 (still in drive @ 30 mph). As soon as the RED light went out, every thing back to normal! The engine is NOT HOT! The dash temp gage works fine and never goes over mid range.
The egnine is running a normal mid range (same as temp gage displays). So my question is what turned on the RED overtemp liight and triggered the ECM to tell the fan clutch to engage as tho the engine was HOT? Any comments welcome.

 

[GLOCKer]

Bad t-stat?

 

[donalds]

Change your thermostat asap use a good one do a radiator flush while your at it