I found the Ambient Air Temp Sensor! 2008 ProStar...

[Waterloo]

(06-10-2019 )Daytripper Wrote:  Well I replaced the ambient temp sensor....still no outside air temp displayed on my dash??? No change in A/C performance either....

Check the wiring under the loom, it may have broken up line, that would be my first guess as to your problem.

If the wiring looks good, Google the Navistar Body Builder schematics on the internet. These trucks run on that CanBus system, it may be a sensor up or downline that is bad that the ambient temp sensor runs through. On my ProStar the ABS brakes and exhaust brake run through the compass. Yes, the compass. I had to replace that to get my engine brakes and ABS to operate. Can't make this sheet up.

And get that valve and switch I linked to above. I just installed both in my 2008 ProStar, nice having heat and AC when I want without having to get out of the truck and under the hood to turn that valve on and off. Best $35 I have ever spent.