20007 Freightliner Columbia AC lines and evaporator to main and bunk freezing solid root cause?

All the ac lines and evaporator freeze solid.
Here’s what it is not:
Not low on Freon
Not over full on Freon
Not the air filter on the main
Not the air filter on the bunk
Not the two pin air temp sensor in the main box.
Here’s a clue
The ac compressor seems to run continuously and not cycling?
Also the ac compressor runs when the the snow flake ac switch is off?
Anyone have any ideas?

 

Clutch powered at all times or no?

 

Yes it seems to be powered all the time for some reason?
When it is unplugged it stops turning so I don’t believe it’s a mechanical clutch issue ?

 

You can see by the dash that everything is off but the compressor continues to be powered up and running.
I go out unplug the compressor and it stops and the lines immediately start to melt the ice.

 

I’d check for a wire rubbing especially if the voltage is a little low. 11-12v

 

Maybe high pressure switch. Should be on or near the air dryer. Might be the expansion valve sticking. If any moistures in the system, it could be freezing and blocking the expansion valve. If blows warm when frozen, probably the expansion valve. If the fans also running constantly while idling, and not cycling off, it might be the high pressure switch. Just guessing. I’d try turning it on and off, and tapping on the expansion valve. Might get lucky. You can also change the dryer, and the pressure switch without evacuating the system. New Dryer might clean up any moisture or trash in the system. Hopefully you can avoid changing the expansion valve and recharging the system. The only other thing, is the temperature probe that goes into the evaporator. Don’t know much about it. Usually if it’s working you can hear it click on and off, with the clutch. It controls the clutch. Then it could be something electrical, or something particular to your Truck. Good Luck.

 

Compressor runs when it’s off? Should only run when snow buttons off, if defrosters on. Does it run with fan switch in off position also? Pretty sure if expansion valves sticking, high pressure switch would cycle it off. I may be wrong about that. Either way, should cycle off, when it doesn’t it’s usually low on Freon or has a bad high pressure switch.

 

Ok
I think I might have made some progress!
I’ll check back in later but now it time for an eight hour road test lol

 

The 8 hr road test was a success!!
Here’s the deal…
I pulled the wiring that goes to the AC clutch out of the loom to check it.
I then noticed it had a pretty substantial wire gauge size.
After seeing that I knew it had to be activated thru a relay to handle that kind of amperage.
So in my head I also knew the only way the ac compressor could be powered full time through the relay when all the controls were off was it was either somehow being commanded on by the system or the contacts in the relay were stuck together?
Well it turned out to be the latter the contacts were stuck together and my poor little ac compressor was running its heart all day and not cycling so it would freeze the system solid.
I swapped out the relay with another relay in the fuse box and it works perfectly now.
I thought it was important to post the fix as to many threads here go unfinished with out the answer to what actually fixed the problem.
Thank you to everyone who posted help to me and hopefully this thread can be beneficial to someone else someday with the same issue.

 

What relay, can you post pictures?