I have been having A/C problems on my 2005 F350 over the summer. During this time, I noticed that the External Temp sensor was way off most of the time -- and read much lower than the real temp. Service rep thought this was the problem with the A/C and we tried new control modules, sensors, etc. Well, today, we found out how the sensor really works from Ford Engineering.

Turns out that the external temp sensor is located near the radiator and Ford knows it will return an inaccurate temp. Therefore, at speeds under 20 MPH, the sensor will not update (to the higher temp side) more than 1 degree per hour. At road speed, the temp will update 1 degree per minute.

Also, there apparently is NO connection between the external temp sensor and the A/C. So, we will have to dig elsewhere to determine what is wrong on the A/C, but at least we know where not to look.

 

Thanks for the informative post, i had been wondering about the weird read-outs i get sometimes- this explains it all. Keep us posted on the AC problem!

 

cody47,

What kind of A/C problems are you having? I too am beginning to wonder about my A/C unit. Seems that when the A/C is working right, it's WORKING right (blows ice cold), but then the temp will just drop off and blow cool air. A few minutes later it will get cold again. If I use the MAX air button, it gets cold right away again. And fan speed seems to have no effect on the temp. Is this normal for Ford Superdutys w/ 6.0PSD? This is the first diesel engine I have owned.

I have a 2005 F350 CC 6.0

 

Why would the fan speed affect the temperature of the air? The two are completely independent.

The compressor will kick on and off, trying to maintain the temp that you set. That is why the air seems cold, then warmer, then cold again. The fan blows all the time, regardless of what the compressor is doing.

The MAX A/C button kicks the compressor on immediately, so the air gets cold immediately, but it too will cycle the compressor on and off depending upon what temp you have it set at.

 

jschira,

I didn't figure that the fan would have an effect on the temp, but in todays new fangled electonics and the way things work, I figured I would just mention it.

I have the temp set to 60* (as low as I can set it) and I do understand that the compressor will cycle on and off. I just figured that when it was set as low as it would go that the compressor would just blow steady cold (like in older model vehicles, work manually).

But, if what it's doing is normal than that's fine. Just wanted to make sure nothing was wrong.

Thank you for your input, now I understand the how the system works a little better.

 

I woinder if more manfs then Ford do that type of adjustment on the temp reading. It would explain why it takes 15min for mom's volvo to read the correct outside temp. Starts out low and slowly climbs up.

 

Doesn't Max/AC engage the re-circulate function for improved cooling. This cuts out periodically to freshen the cabin air.