Automotive Air Conditioning Information Forum

DetroitAC wrote: ↑Thu Aug 26, 2021 5:36 am I think the extra port on the evap is for an IHX integrated into the evap, basically a little heat exchanger transferring heat out of the liquid refrigerant and into suction gas, these are pretty common on current production cars, but they are in the suction line pipe, not in the evaporator. Evaporator room is usually too precious to fit something like this, takes space away from cross car structural beam, infotainment, glove box, airbags, etc.

This seems to make sense, I can actually see what looks like a small heat exchanger on the side of the evap. I still cant figure out how this is done with only 3 ports though. It looks like there is a liquid line, suction line, and then another branch off the liquid line that goes through a pressure regulator and then to the IHX. I cant figure out how the liquid feeding into the IHX circulates out of it though.

I just wanted to document a few things here since I have undertaken a pretty big project on my Lexus. The goal was to get coldest air possible this summer however it was more experimentation and learning process. The main changes I set out to make were:
1. Increase the TXV capacity (1.5 ton to 2.0 ton)
2. Remove any unnecessary valves etc that are restricting flow and install a cycling switch to prevent freeze up
3. Add a second condenser in front of the factory one to increase condensing capacity

What I learned through multiple trials and errors was a few things.

The EPR is a spring loaded mechanical valve that is pushed open by the flow from the evaporator to the compressor. The pressure drop across the valve is what provides the opening pressure. I decided to delete this suction side restriction and go with a cycling switch.

The "pressure regulator" mentioned earlier is a TXV bypass valve of some sort. It is a parallel branch from the liquid line to the evaporator inlet. It has a power head on it and a valve inside. I am attaching a picture. I still cannot honestly say after all the testing I did what the purpose of the valve is. I can only assume it acts like another TXV in parallel with the main one but for what purpose I don't know. Potentially it could provide an alternate path for refrigerant flow when the main TXV closes down due to very low pressure on the external equalizer line that senses between the EPR and the compressor inlet.
There are two inlets on the evaporator - one from the TXV and one from the "pressure regulator". I purchased a Four Seasons aftermarket evaporator and found that one of the two inlets, the one from the "pressure regulator" was blocked off and went nowhere. So somehow the system is able to operate with the "pressure regulator" unused/plugged with the aftermarket evaporator.

I changed the TXV from a 1.5ton externally equalized to a 2.0ton internally equalized. I figured the external equalization was to deal with the massive suction restriction that was the EPR, and that with the EPR removed was no longer needed. I was wrong. When I charged the system the low side would suck down to about 5-10 PSI and high side would refuse to come up above 130psi. I found that the plate/fin evaporator was enough of a pressure drop to cause the P2 pressure in the TXV to rise and close the valve. So I am switching back to an externally equalized TXV to overcome the pressure drop of the evaporator.

This pressure regulator device is still a head scratcher for me. I cannot figure out why this would be here nor can I find anything like it in any other Lexus or any other AC system in any car. I also found that the factory evaporator was very restrictive when deleting the "pressure regulator" circuit and just relying on the TXV. When I blocked it off the low side sucked down to almost 0psi and I found little temperature drop across the TXV but icing on one section of the evap. Apparently the internal passages in the evap are pretty restrictive and cant flow enough to fill the main section with liquid unless the "pressure regulator" is installed. The aftermarket evap circuit was different and didn't need the "pressure regulator" to flow properly.

I commend you if you read all that it is more to document my own findings and maybe help someone in the future if they happen to dig into the LS400 system.
I am hopeful that the second condenser does help me get some extra performance out of the system in combination with removing the EPR valve. I will update once the AZ sun comes back this summer.

Here is a picture of the "pressure regulator"

hi
Doubling the size of condenser in a standard size car unit will give fully charged high side of about 150psi -160 psi on a very hot day eg 100--110 f . RPM 1500rpm A partial charged system looks as if there is some thing wrong . U will see alot lower on an almost full charge especially on a 80F ambient day .

The first pic is an externally equalised txv .
All the GM conversions I do have a block TXV 2 ton 4.4cel s/heat which of course is internally equalised and electronic thermostat . work fine . The GM evaps have originally an external equalised txv as per pic .

I'll bite.

What's your plan to double the condenser size on a 1999 Lexus LS400?