What happens when capacity of system is exceeded?

[cyfi66]

It has a regular externally balanced TXV, but there is also a pressure regulator on the evap - its purpose I dont really know. Maybe something going on there.

If the TXV were to open up more to allow more refrigerant in the evap, wouldnt that drive up the low side pressure and reduce the superheat but also increase the saturation temp in the evap?

And like you said who knows what the superheat is supposed to be by design. It could be that the TXV is "underfeeding" but working as intended. I think we already established that Lexus primary objective probably isnt ice cold air in hot climates. Is there a way I could pick an aftermarket TXV that I know will meet the demand and use that instead? Or test the factory TXV on the bench with some air lines rigged up to see if the max flow of the TXV is sufficient for what I am trying to achieve? Its also possible the TXV is working as it should but the EPR is choking off the suction line before the compressor (or would the superheat still be correct if the suction line were blocked?).


Ill see if I can get some more simple data at 0, 5, 10, 15 min under "normal" conditions where the windows are closed and I am using it just like I normally would.

I would have to check the liquid line temperature but I saw just a couple bubbles in the sight glass on the drier at idle.

[tbirdtbird]

That EPR is the fly in the ointment. No one really seems to know much about it, and we have some brilliant experts here...... (I am not one of them)

[cyfi66]

That EPR is the fly in the ointment. No one really seems to know much about it, and we have some brilliant experts here...... (I am not one of them)

Isn't the EPR really just a POA valve? From what I understand POA valves are pretty well understood and were common in some applications.

[bohica2xo]

We understand the EPR / POA valve here quite well. However there is little or no baseline experience with that particular POA valve.

Is it just too small? Set too conservative? Just fine? . All possible.

I suppose you could build a bypass connector and remove it from the system for some testing.

You could certainly bench test it to find the current setpoints.

[tbirdtbird]

Sorry, Bohica,no offense intended.

I found this EPR writeup in the archives posted by Dougflas 11 yrs ago. He states he got it from an old Mitchell manual.
It is for a Chrysler, but I would assume the concepts are the same. Maybe the Mitchell has the writeup for the OP's Lexus....

https://www.autoacforum.com/messageview ... adid=22009

[cyfi66]

I am planning on buying a used EPR so I can take it apart and possible gut it out. It looks like it is all crimped together so I will probably have to weld it back together when I am done.

I wish I could test mine like that, but there is no service port between the EPR and the compressor so its impossible for me to know what the pressure looks like there.

[tbirdtbird]

Were it mine, I would ditch that gizmo, and plumb it up in a more modern, simple way. I would fit a traditional TXV, and frost switch embedded in the evap. It would take some messing around, but if I wanted to keep the car, I would be done with that hocus pocus EPR. If Bohica and Detroit are not familiar with that particular rendition of an EPR then all bets are off

You would need to be able to use another car in the meantime. Of course we do a lot of custom AC work here so we wouldn't be afraid of it.
Why not wait till whenever you have winter in AZ and mess with it then

[cyfi66]

Thats the route I am leaning towards. I really love the car and want to keep it I would love if the AC was a better performer. I am also planning on doing a second parallel flow condenser stacked in front of the existing condenser to give a little more condenser capacity. I would prefer to go with an H block TXV mounted at the firewall ideally but that might take more fab than I can handle in my garage. This isnt my only vehicle so downtime isnt really a concern. How would I go about selecting the proper size TXV? This will probably be a winter project this year since I am not working in the garage at 100+ degrees.

Do you know of any fab shops that would take on some of the custom lines and things like that in the AZ area?

[tbirdtbird]

Tim surely knows of someone that can do custom hose. The experts here are all from hi-temp areas such as AZ and NV, someone will know.
JohnHere has referred ppl to ColdHose in FL but I am sure you do not need to ship that far.

I am gonna guess you would need a TXV rated at 1.5 tons but now that you have made this decision I would think Bohica or Detroit could better advise.

[tbirdtbird]

The EPR would be gone and I'd suggest an internally equalized TXV, which we use all the time

All you need to make AC happen is
comp, cond, FD, TXV, evap