Air Conditioner Problem 3 shops can't find problem so far

Think thats what mechanic was talking about today when I mentioned this guys problem. Something about 2 sensors and they have to be within certain degrees to tell the ac pump to engage? This make any sense.?

 

Those are the thermistors. They are located on the passenger side, about eye level, one is on each line by the dryer cartridge. They have two wires to each sensor. The system needs to be evacuated to replace. They can be tested with a multimeter. They control the signal to the cab controller, they read the line temps. They used to go bad quite often, but they were redesigned and in my experience now rarely ever fail.

 

That is not good, and HeavyD is correct, that looks like failure time, you cannot run the compressor like that. Get the truck to a dealer and let them diagnose. You need Diamond Logic on there to diagnose exactly what is going on.

These AC systems on these ProStars are ran through the cab controller and a thousand other can bus modules. This is not your old school AC systems. Sometimes the dealer is the best place to start, God knows I have had to go there more times than I would have liked to, as I do not have a copy of Diamond Logic. Sometimes it is the only way to properly diagnose.

Do that first. One other thing I did to get my system working, blowing cold, is to remove any die from the AC system. I run straight refrigerant. That and moving that Ambient Air Temp sensor and I have had no issues with the system. It now works. Your system holds 3 lbs of refrigerant, if you have a sleeper with its own AC system, and is very finicky about that too. It can be a little light, but go over that 3 lbs and trouble awaits.

 

Your truck is a 2010+ model. It no longer uses thermistors. If your guy is using Diamond Logic builder software, these are the interlocks that must be met for the body controller to turn on ac compressor;

• Ignition and Accessory voltage at body controller (Checkmarks at A1 and A16 at 1602 of B/C)
• Air conditioning request from HVAC control head to B/C (Checkmark at 1600_A2)
• Engine running signal (Engine_Running)
• Engine speed above 300 RPM (Engine_Speed)
• Low pressure input is grounded (Checkmark at 1600_B5)
• Freeze Probe Thermistor input is ≥ 38° F ( HVAC_Freeze_Protect_Raw above 2.4976 volts 1600_B13)
• A/C high side pressure is greater that 35 psi, but less then 218 psi (AC_High_Side_PSI) - Pressures may change due to programmable parameters. See table below.
• No HVAC fault codes active

 

In one of your earlier posts you mentioned you put voltage directly to the compressor to make it work and it worked. I have heard many examples of this issue involving other accessories that were fine but had to receive direct voltage to operate. In those cases the root cause was the vehicle ECM. The ECM on a modern truck controls EVERYTHING, I’d have them look at the ECM. They can hook the computer up to it and turn parameters on and off with a push of a button. I’m betting that there is some damage to the ECM preventing the operation of the compressor.
Most mechanics are just going to throw parts at it. Find someone that will at least check and see. It wouldn’t take but a few minutes to see if there is a malfunction in the ECM related to compressor function.

 

The ECM is the module on the motor, you are referring to the Cab Controller or Body Module which controls the cab functions, like the AC. These new systems are a nightmare for the average shade tree mechanic. Just diving in with a set of wrenches is essentially a waste of time and money without hooking up a computer first.

Here is a good example, my ABS and Jake/Exhaust Brake idiot lights would flash on and off for no reason that I could identify on my ProStar. I took the truck to the dealer and they hooked up Diamond Logic... The computer said it was the compass? The compass? My ABS and Engine Brake go through the compass? I didn't even know I had a compass on the truck, as nothing showed up in the cluster.

I asked if they had one in stock, no. I asked how much, he said $350. I said give me the part number. I bought one on eBay for $19.95 locally, had it in two days and installed. It is the size of a Zippo lighter and is mounted in the dash above the fuse block with two screws.

I was ready to start tearing into the ABS system, when here it was nothing of the sort. It was a compass! They route the ABS and Exhaust/Jake Brake through the compass? I never would have figured that out in two million years.