Truck is a 2002 F250 w/ 7.3 diesel. Has 346k miles. Unsure if any AC components have ever been replaced.. possible given the mileage but then again, ???.

Last fall a shop recharged the system and added dye. After a few weeks I used UV light and yellow glasses at night to try and spot any leaks.. couldn't see anything. Over time the system started blowing lightly cool to warm air depending on outside temp.

I took these readings when the temp was about 80 degrees outside.

 

Low refrigerant charge.

 

Agreed, low on charge.

I use this as my go to:

 

Added refrigerant this afternoon, temps were pushing 92 degrees:

Added first can of R135a, and the low side gauge barely moved. Added another.. same deal. Air temp at vent was 60 degrees F. Compressor engaged the entire time.

After the third 4oz can of R134a, I discovered that the gauge itself appeared to be falsely reporting pressure. More to come.

 

Off to Harbor Freight I went. Got their gauge set at the tent sale for $49. It seemed better made than the set I got from Amazon.

Got the truck home and hooked everything up again.. Had to triple check the low side which was pegged full. High side was around 250.

I'm a bit confused about the different readings between two brand new gauge sets.

 

4 Oz. cans? Really? Those are tiny!

Video 2 , the first gauge set... Looks like that gauge set has the check valves in the hoses, at least on the LO side, that is why the pressure stayed the same on the gauge after you disconnected it. It's retaining the refrigerant in the hose, rather that just blowing it out the open hose end, like they used to do. Without it connected to the system, you could attach the hose end to a spare LO-side service port, like one off of an old accumulator, or a disconnected in-line LO side valve to discharge it, but don't tell anyone I told ya that
But as long as it is properly connected to the LO-side system port, it is reading properly from what I see. And the LO-side pressure not climbing with small amounts added is expected... you will see the effect in the HI-side,

Video 3, I do not for-sure know why your LO-side gauge is pegged over the Retard zone.
I'll throw out a possibility: Could the coupler wheel out at the end of the LO-side hose be CLOSED, and the valve wheels up on the gauge manifold for both HI and LO not be seated tightly (snug, don't murder them). Thinking maybe leakage from HI side hose through HI-side wheel valve, to center manifold section (anti-blowback valve in Yellow charging hose preventing release that way), through LO-side wheel valve, to LO-side gauge. Just a thought.

 

If you look close there is refrigerant visible in the clear glass bubble in the manifold. The possibility of user error is extremely high as this is my first experience using gauges like this.

 

Have both ***** on the gauge manifold closed and both ***** on the hose QD's dialed all the way in. That opens the schrader valves on the gauge ports on your truck and the gauges read the pressure in the hoses. You only open the ***** on the gauges when you are either adding refrigerant or reclaiming it.

I have those same gauges, and there is always the Harbor Freight chance you got a bad set right off of the shelf and the valves on the manifold are leaking by even if they are closed.

 

Will recheck tomorrow/today after I wake again. When the time comes how do I discharge the old refrigerant (legally)?

 

i do not use lights or dye to look for leaks. i use a sniffer.
if the leak is in the evaporator the only way you will find it with dye is to completely take the cab apart. with a sniffer you will know as soon as you put it to the vent.

 

Will Autozone rent the sniffer?

 

don't know, i do not deal with them.
you can buy a cheaper one for around $25. brand name units go as high as $450

 

After looking at the video again, there should be no way possible the low side psi is higher than the high side with the way the valves in these compressors work. My guess is a faulty gauge. A possible 500 psi low side would most likely blow a fitting or hose connection apart. The compressor usually has a relief on the high side that will vent to the atmosphere if it goes over 350 or so.