Help with 2008 A/C diagnosis. A/c not kicking on. Blowing warm


Jake - 2008 Frieghtliner 3500 170ext Mega Roof
I recently purchased a 2008 170 mega roof Freightliner sprinter. During initial test drive, I noticed the AC was not blowing cold. I discussed with the owner and he had said it was working just a month ago, but hasn’t used it since. Well I needed to drive it to Florida so I needed AC working before making the drive. He offered to take it to his mechanic to check it out. Since it was the exact model I was looking for with the extra high roof, I was willing to work with him

Long story short, the mechanic drained the system and refilled it. AC WORKING blowing ice cold:thumbup:

Drove that evening for 6 hours until I made it to Virginia. Ac working beautifully. Spent the night in a hotel, got up the next morning, drove for another 3-4 hours while the ac worked great (it was in upper 80’s going through the Carolinas). Stopped for 10 minutes to grab lunch, came back out to the van with NO COLD AIR COMING FROM AC. Noticeably not cool air coming from vents. Well it was a long and not 8-9hrs to south Florida, frustrated, but happy to have secured the van for our build.

Confused at how it could go from working to not working so quickly. A friend and I have checked the fuses, none of which are blown. We connected the compressor/clutch to a 12v battery and it gives us a click sound. Could the Freon in the system be low, causing the pressure switch to stop the ac system from engaging?

We tested the wire going to the compressor with the van running, and ac turned on, and got a 0volts reading, when I’m assuming it should be 12v going to the compressor.

Thinking of having the pressure tested. I guess my question is, will low pressure set off the ac pressure switch, causing the system to NOT cool

Thanks so much in advance, been combing through these forums, so much information and different scenarios. Figured with all the knowledgeable members I might be able to get to a solution quicker by (and this is VERY hard for me) asking for help..




Active member
It's probably leaking. The leak should be easy to find as there will likely be a mess of refrigerant oil around it.

I found a workmanship assembly defect that was an issue on my 2008. There was a wire pressed against the condenser, and eventually created a hole in it.

I used a crappy product for the solder and flux, it's just what was available locally in a pinch. It's still holding though. In the spring I'll probably go in there and resolder it with a better quality solder/flux for Al.


Jake - 2008 Frieghtliner 3500 170ext Mega Roof
Thank you so much for sharing that. I plan on running a leak test, but before I will take your advice and physically inspect that area. Again thank you for sharing that!


2015 long/tall limo RV 2.1l
When refrigerant leak is main suspect, the system operates with at least 7 different sensors, so lot of things can malfunction.
MB makes digitally-controlled, dual or more zones systems for over 20 years, where display changes, but the main components are the same.
Here is the best help site I know. It shows model who could pull sensor values on climatronic, where you'd have to use scanner, but system allows for 90 seconds troubleshooting with clean hands.
Cold/morning sensor reading is for checking calibration, while hot day reading actually shows system performance.


2015 2500 short tall 6cyl
My 2015 had similar symptoms. Went to have it recharged and they found it very slightly low, so topped it up, but still wouldn't work. Eventually they diagnosed it as a bad connection on the high pressure sensor connector. Some fiddling with the connector got it all to work again, and I now know where it is in case it starts to act up again.


New member
Had the same thing happen on my 2008.
Drained and refilled the system. was still working on and off
The high pressure sensor was faulty.


Jake - 2008 Frieghtliner 3500 170ext Mega Roof
Where did you source a new high pressure sensor and what do they run? Going to check the connection of it tomorrow. Where exactly is it located


Jake - 2008 Frieghtliner 3500 170ext Mega Roof
I’m aware you can’t remove it without draining the system

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