AC guys please help

I’ve rebuilt just about every part of various cars and trucks, but there’s 3 things I leave to the pros. Automatic transmission stuff, body and paint, and AC recharging stuff.

 

This is about the only good reason I can think of to suggest taking it to a shop

OP - AC isn't rocket science. I bought a vacuum pump and pressure gauge set when the "professional" AC places couldn't figure out why the cooler in my wife's car wouldn't hold a charge. Three different shops, three full charges of r134a lost, hundreds of dollars wasted. You can guesstimate how much you need to add buy putting a bit of r134a in and watching the gauges until they get into the published pressure ranges.

I'll bet a dollar there's a leak somewhere. Putting more r134a in will get the cooler working again, but only temporarily. One last thing, and this is important, DO NOT PUT ANY TYPE OF STOP LEAK IN THE SYSTEM!

 

Hell yeah!
And if I could figure out how to post a PDF from my pc to here I would. I am not a smart man.

You're compressor should shut off when the low side drops below ~28 psi. Obviously it is not. The pressure switch is in the liquid line (line from condenser to TXV.) It is possible that you have a blockage at the TXV or the filter screen just ahead of the TXV.

I would pull the charge, check that screen, pull a vacuum, then weigh in 22oz of freon. What are the gauge pressures now?
The pressures you posted are not the same as a system that is just low on freon.

 

^^ this

 

@DBiffle was your pressure dipping into the negatives under throttle? That's what surprised me.

 

Thanks @CurtB I was hoping you'd chime in. I'll do exactly what you said. Evacuate the refrigerant, pull out the screen and check, pull a vacuum and recharge then take another reading. Just gotta wait for the weather to warm up a bit to recharge.

Is there a way to check if the expansion valve is stuck closed or partially stuck?

 

Cant really check the expansion valve until you're sure its got the proper charge amount in it.

If the system was full and the expansion valve was stuck closed you'd have a hell of a lot more high side pressure, like up over 300 psi

Your readings indicate an empty system

 

@Clearwater Bill which line going into the evap is the incoming line? The big diameter or the smaller diameter line?

 

The small one

 

I wouldn't disassemble anything yet, charge it and see where you're at

 

Thanks bro, no pun intended.

 

You have the gauges so follow the chrisfix video and throw some r134a in there. Make sure you buy pure r134, absolutely nothing with stop leak in it. It’s much cheaper to replace the leaking part and or o rings than the issues the stop leak can cause in the future.
Only advice is make sure you have a vacuum pump if you plan on opening the system so you can get any moisture out.

Also before you open the system take it to a shop to have them recover any refrigerant in the system.

Once you have charged the system to test for a bad expansion valve run the ac system and make sure the compressor cycles on. Then shut the vehicle off and watch the gauges. They should slowly return to the same pressure. It may take 5 minutes or so. If it’s taking longer you may have an issue with the expansion valve.


Some people over complicate ac systems. It’s very simple and the only thing most DIYers should worry about when doing them is getting the system evac’d with out venting the r134 to the atmosphere.

 

Yes, after you have the correct amount of freon in the system.

 

But, why isn't the low pressure switch cutting out the compressor? Possibly a bad switch and low on freon?

 

I used the term "empty" in a general sense. Undercharged is a better word

 

Yes, I know what you meant. My point is why the LP didn't work. I have a theory If the screen is clogged, or the TXV is not opening, there is pressure up to the blockage. The LP/HP switch is one unit, in the liquid line, before the screen and TXV. This would keep the LP from cutting out.

So empty the system, add 22oz, and read the gauges. Then you will know if there is a blockage. That is where I would start, and I would check that screen while the system is empty. And use new O-rings.

 

Also oil the new o rings with compressor oil. If you don’t do it then don’t be surprised when they leak. Ask me how I know.

 

I hear ya, but he would have a lot more than 75 psi on the high side if there was a blockage.

He had 75 psi engine off and 75 psi engine running. If there was a blockage that 75 would have to go up

In my world, ac diagnosis always begins with verifying the correct charge amount is in the system. Thats hard to do without proper equipment. You can spend a lot of time fiddling around with a system if you dont know how much refrigerant is in there. Simply hooking up the gauges and looking at static pressure isnt enough info. It could read around ambient temp with a full charge.. it could also read around ambient temp with a very low charge..

I agree the LP switch could be a factor, but need to start with the charge amount..

 

Yup. Years ago I was in a hurry ( I was completely stupid) and just hooked up the low side and started charging by pressure. No scales, no nothing. The sight glass had bubbles tho. When the high side hose blew, it got very exciting.
<Idiot

 

Yes, scared me when I first seen it.