Automotive Air Conditioning Information Forum

GottaBeCold88 wrote: ↑Wed Jul 27, 2022 1:09 pm According to my calculations, I'm at 20* Subcool, at 32* Superheat.
(By the way, you'll see two numbers in the low pipe temp column, as I was asked to measure both pipes coming out of the evap. They were very close to each other, but the #10 was 1-2 degrees cooler than the smaller one)
So, if turning the TXV screw out 1 turn lowered my superheat from 38 to 32, that's 6 degrees. To get down to around 10, I need to lower superheat by 22 more degrees. If one turn got me 6 degrees, I need to turn it out another 3.66 turns, making 4.66 turns total from how I received the TXV.
Does my logic check out? And, will the screw even turn out that far without falling out of the housing?

My two-cents worth: Presuming that the 32°F superheat figure is accurate, and also allowing for the now re-adjusted TXV, the system is undercharged. Simplistic, I know, but that's the way it seems to me.

Recall that the stock system takes 44 ounces of R-12 without rear A/C. Your custom set-up has hoses and lines that are considerably longer than stock, making the original 44-oz. specification seem like it's on the low side. You're at 37 ounces now, I think you mentioned.

And about the superheat adjustment screw: I would hesitate to turn it out that far. I never tried, but if the screw loses contact with the spring, the screw will become loose. It might even fall out, as you suggest, depending on the length of the female threads. But I don't know that for certain.

DetroitAC wrote: ↑Wed Jul 27, 2022 7:09 pm OK, but you measured those temps where I'm pointing in this picture, correct? 76F after the TXV, before the evaporator? Please confirm

I don't think adjusting the TXV was good advice based on this,

Yes!! This is absolutely correct. You got it.

OK, I think the TXV is not the problem, I think it's actually overfeeding now. I think the evap exit superheat is not 32, more like 0 to maybe 4. The reason is pressure and temperature not measured at the same location and big pressure drop in between locations.

My best clue is the evap inlet pipe temperature, and i have no idea how your evap is constructed, like what kind of tubes, what kind of refrigerant side pressure drop, but they are generally low pressure drop devices, I have to assume yours is too, like maybe 10 psi at the most for a state of the art modern evap, these older technology units are usually very low pressure drop, simple tubes that are easy to manufacture, I'm guessing only a few psi pressure drop.

Your suction line pressure drop is the problem I think. Is it kinked or squished flat anywhere? any chance you can change to #12 hose? Every crimp you make also adds pressure drop, I'd suggest no fittings except the end fittings, and place LS service port at the compressor, not sure if that's possible.

I appologize for steering you wrong direction, if I was there in person my fingers would be feeling the temperature of every pipe.

Dang! This is a bummer. OK I will order some #12 reduced barrier hose, hopefully it will fit in the a-pillar. And I can put the port on the compressor, sure. I can also get rid of the inline service port, and the fittings that go through the bulkhead at the firewall. That's two more fittings I can toss—I'll replace them with a rubber grommet.

You reckon that'll do the trick? Also, should I get an expansion valve while I'm at it? Worried the one I have might have some issues or something.

Wondering, before I go through will all this should I try putting more r134a in it?

Detroit, had an idea to test your theory that could save me some time and effort. I have some left over parts from the build—what if I temporarily put another service port up by the evap unit? I could disconnect the #10 line at the evap, put in a short line with a service port fitting right at the connection for the evap. That way I could get pressure and temp right at the same spot.

When I get temps with my IR gun at the service port under the hood, they are very hot. My theory is this is due to heat soak but you guys may disagree (you know better than me). I will say it is quite hot in the cramped engine compartment with the van sitting still.

Another possible benefit of splicing in this temporary in cabin service port is I could also compare pressure at the evap and the under hood service port I’ve been using this far. Just a thought.

A second service port is a great idea to confirm

I believe your subcool measurement. I think more charge will just raise condenser pressures.

Based on what I know, I don't think there is anything wrong with the TXV, it's controlling your low side pressure consistently, and we have no idea the real superheat until you get a measurement with the new port

Okay cool. I Actually think I could pop this bad boy in and not even have to make an extra hose... just put this between the existing #10 hose an the evap unit. Thoughts?

https://coldhose.com/collections/all/pr ... 1745788064

You guys are scientists. I'm starting to feel like one too.
I really hope we can figure this thing out. Thanks for all the help.

GottaBeCold88 wrote: ↑Thu Jul 28, 2022 10:50 am You guys are scientists.

I actually am !!!

I'm a retired R&D industrial analytical chemist, soap and detergents.