A/C Expansion Valve Replacement

[Meezy237]

I replaced condenser compressor drier & high pressure switch also on/off switch on high side before I changed out switches mobile mechanic added jumper to compressor while charging it started cooling recommend I changed out both switches I changed those after a few days but still not cooling so I’m going to replace the expansion valve which I was told by another mechanic that it should have been replaced when I changed out majority of the system…when I vacuum system will I need to add oil back into the system or it should be fine ?

[Joey Mack]

What are you using to recover the freon? 

[Geoff Weeks]

Hold on! while it is possible that the Tx valve could have a problem, given what you have said so far, I would find it highly unlikely.

When I started doing A/C work, I also heard that maxim to replace the Tx when the system is opened. Experience has taught me different. I have NEVER had a Tx fail other than mechanically. In other words, the fitting or tube connection fail, and a easily inspected without removing.

I have seen far more damage done when people try to replace it for no other reason than "the book tells me to when I open the system".

I ran some experiments on my own systems, and found that in most cases (all I had) that replacement wasn't necessary.

 You can tell when they are bad via pressure readings  and "superheat" measurements. Given what you have stated so far, the chances the problem is the Tx are much less than 2%.

So lets address your problem and diagnose the system. Did you add the correct amount of refrigerant by weight? When you replaced all that stuff, did you add enough oil to the system?  What are the pressures now, both static and running pressures? What is the air temp across the condenser?  Does the truck have a sleeper unit also? Did you go over the system with a "sniffer" looking for leaks? Does the engine fan come on at some point with the A/C operating?

It is far more likely you have a leak than a "stuck"Tx valve.

As an experiment, I took one of my systems that was open when I bought the truck (condenser was missing) and had been for at least 10 years, I installed a condenser and rebuilt compressor but DID NOT change the Tx, and it worked just fine! If any Tx was going to stick, it is more likely that one would have. Years later I did change it out when the equalization tube nut rotted off the suction side elbow, the Tx itself still worked.

 

 

[Meezy237]

System takes 48oz=3lbs no sleeper 

added 8oz of oil due to what came out out of old compressor 

static pressure low side 70 High Side 70 when I started the engine low side rises to 80 slightly rising High At 80 slightly rising also went around  with a sniffer only thing hitting it schrader valve evap coil looks good 

maybe I’m thinking cab control unit 

[Meezy237]

Air vents not equal air flow 

[Geoff Weeks]

Right off the bat, I'd say the compressor is not compressing, either the clutch isn't locking or the compressor isn't functioning. check voltage to the clutch.

A Tx valve doesn't "open and close" it is a restriction, that gets bigger or less so, but is always a restriction between the high and low side.

Forget the Tx valve and take a hard look at the compressor.

Edited Friday at 09:01 PM by Geoff Weeks

[Geoff Weeks]

At those pressures I would say air temp is around 76 deg F

[Joey Mack]

Can you recover some freon so it's down to 50+ psi on the low side and see if it kicks the compressor on.  It takes 50 psi to signal the compressor, then add freon and test as you go. Not going over 3 lbs. Assuming you have a Robin Aire type of machine with a scale..

[Meezy237]

On 4/25/2025 at 4:00 PM, Geoff Weeks said:

At those pressures I would say air temp is around 76 deg F

At the plug  might go to -.112v but I switch hvac relay some model have an actual a/c clutch fuse cb53 but don’t have it on mine 

[Joey Mack]

Oh hell. Your working on an MP ,,, those A/C compressors have a hidden clutch, so good old diagnostics wont work. Is the compressor new? Does it have an APADS type system on it ?  

[Meezy237]

Compressor is few weeks old how could I tell if it has APADS?

[Geoff Weeks]

On 4/22/2025 at 10:23 PM, Meezy237 said:

I replaced condenser compressor drier & high pressure switch also on/off switch on high side before I changed out switches mobile mechanic added jumper to compressor while charging it started cooling recommend I changed out both switches I changed those after a few days but still not cooling so I’m going to replace the expansion valve which I was told by another mechanic that it should have been replaced when I changed out majority of the system…when I vacuum system will I need to add oil back into the system or it should be fine ?

Re-reading this, what I see is it cooled when the mechanic "jumpered" the compressor. Now it doesn't without the jumper. Either wrong switches (if switch type is used) or an APADS problem if that is used.

In short, you have an electrical problem not a refrigerant system problem.

[Joey Mack]

They are typically mounted below the left windshield, in a visible spot standing next to the truck.  Its a small black metal box with a row of L.E.D. bulbs to read to monitor the health of the system.