Unusual A/C Compressor Issue

[PierreR]

Did he just vacuum the system down to check for leaks?
No pressuretest before vacuuming it down?
Not adding dye was not a smart move as it makes it very easy to spot leaks with a uv-light.

I have had some weird things happen to me when i work on ac systems at work.
In some cases there can be a very small leak in a hose or o-ring and when you then pull a vacuum on the system those small leaks can close themselves and o-rings can change their position making it look like the system is sealed.
But when i do a pressuretest with nitrogen those leaks will reveal them selves becase then the pressure opens them and put different load on the o-rings.

An example from this week:
Was working on the ac system on one of our cat front loaders.
The problem was that as soon as the system was charged it would work for 1-2 minutes and then it would stop.

I put pressure (10bar/145psi) on the lowside for over an hour = no leaks
Did the same on the highside just for fun (not really needed) = no leaks
Hooked the machine up and vacuumed it down and then let it hold vacuum for over an hour.
Also no leaks.
Filled it and started it an sure enough after 2 minutes it was almost empty again so it stopped working.

Did everything once again but this time i took my uv-light to look for the dye that we add to the oil.
Then i could see it everywhere on the backside of the clutch = shaftseal.
My guess is that the system is able to hold pressure and vacuum when the compressor is standing still but as soon as it starts to move everything leaks out.

 

[tony1679]

HAHA!!!! We have a winner! Drumroll please......

Jetronic guessed right!

Originally Posted By: Jetronic
is your evaporator sensor reading low temps, causing the cycling?
I have no idea what it was reading, but after jumping through several hoops to find a part number and order it, it did indeed stop the cycling. Thanks to everyone for all the help and advice!

To those that are wondering, or to those that stumble upon this with a search engine, here are the details:

Chrysler part number: 05061064AA - Air Conditioning Probe (Also called A/C Evaporator Temperature Sensor)

Here is an image of the part. The metal piece is inserted directly into the evaporator fins.

Here is a diagram, this probe is identified as "12" and goes into the circle just above it in the pic.

This part is unfortunately a dealer-only part. List price is $51.85. I was able to obtain it at the employee price of $35.78. This part SHOULD (not 100% positive) fit all 2001-2004 Dodge Dakotas. I do know it fits many other Chrysler/Dodge models. Yes, apparently this part CAN make a compressor short cycle. Yes, this part CAN be replaced without taking a single screw out of the dash (at least on Dakotas). It is on the passenger side just below the glove box, close to the cup holders. Just watch very closely how it fits in, and how it comes out, because for me getting it back in was strangely a little tricky. Hope this helps someone!

 

[The_Eric]

Good to hear you got it figured out! Thank you for the update.