Rad cooling fan cycling with AC - blowing warm- Check the relay

[Chuck W]

The past couple of weeks have been big time AC weather.
I noticed that while sitting in slow traffic, the AC would blow warm-ish (or not as cold) out of the vents.

The system is full of freon and the compressor is engaged w/o stopping. What I noticed was that the cooling fan would cycle ON-OFF every 10-15 sec, when it should be ON(LO) when the AC is running. Especially on a 90*F day. It always has before. While moving., or if the engine was hot enough for the HI speed fan to kick on, things were fine.

I tossed in a known good AC pressure sensor, to see if it was flaking out (I could see the system pressure rise/fall on the AC gauges when the fan was kicking ON/OFF, which tracks with the loss of heat exchange). Due to the way I have my logging set up for the ECU, I can't get realtime readings from the sensor in the 850 OBDII app while running (and I didn't want to drag out the laptop).
That didn't solve the problem.

Next obvious culprit would be a failing fan relay. Grabbed one from the stash last night and tossed it in. Viola! the rad fan functions as it should.

I'm temped to open up the fan relay to see if there are any failed/failing components (like a bad capacitor, like in the fuel pump relays)

Just another thing to be mindful of if your AC starts to blow warm. Check the fan function, as well as compressor engagement.

[Chuck W]

As a follow up.
Here's a pic of the fan relay innards.



You can see that the contacts for the LO speed fan (L) are kind of burnt compared to the other side. This did correspond with a bit of corrosion on the plug terminal for the LO speed fan trigger. It's possible the voltage for the trigger signal was a bit weak, due to the corrosion, and not allowing the unit enough voltage for maintaining a good contact.

I'm going to clean up both the contacts and terminal and put it on the shelf with the other spares.

[erikv11]

So rad!

[abscate]

I'm going to clean up both the contacts and terminal and put it on the shelf with the other lost spares.

Edited for Neil and me