Continued from my previous thread: Plans for 90 civic A/C rebuild with newer gen Sanden compressor - remaining questions

[90efAACIF]

""I know this sounds unorthodox, but could a detergent (surfactant such as Dawn dishwashing liquid + water) under pressure be used as a pre-flush before traditional flushing solvents to save on solvents"

Egads, how in the world did I miss this???!!!
Hopefully you haven't actually done this, because the system would never run correctly after such a flush. Ever. Anything put into an AC system has to be non-polar. Period

No I haven't done this. Nor would I do it if a line was connected to any other system component. This was purely speculation, and what I envisioned would only have been done on a short single hard line section at a time, and dried out completely before repeating the process with proper flushing solvent.

Currently the hard line sections (seven individual pieces) are all separated at each fitting and removed from the vehicle, and I plan to bring them that way to whichever shop to do the flushing, dry them out and immediately cap each piece at each end. After each piece was completely done only then would I reassemble the system with new lubricated o-rings, new parallel flow condenser, new evaporator, new TXV, new hoses and then bring the vehicle back to the shop for final connection to a new drier and the compressor connected to the new hoses, evacuation, leak testing preferably with nitrogen and an ultrasonic detector, re-evacuation and charging.

I want this system still working when they put me in my grave.

I am reluctant to do the flushing myself because I have a health issue that requires me to avoid most chemical exposures.

[90efAACIF]

Almost forgot, there will also be a new binary pressure switch with higher cut-out pressure (455 PSI as in the 94+ civic w/R-134a) to allow operation at higher ambient temps / humidity without premature compressor shutdown.

I'm also replacing the temp sensor in the evaporator since everything is torn down.

[90efAACIF]

I’ve had to postpone this project for almost a year. Sometimes life gets in the way but I’m back to it now.

At this point I’m dealing with selecting a replacement TXV, which should have been straightforward but the two main aftermarket manufacturers disagree on their superheat spec, (UAC = 4.0, part# EX 10013C vs 4Seasons = 8.0, part# 38872).

I have been trying to learn the significance (or not) of this magnitude of a difference and called both manufacturers to hopefully get to the bottom of this. Both manufacturers confirmed their spec as found in their literature and both confirmed their competitor’s spec as different. Neither were able to definitively answer why the difference exists or its significance. Both stated that they have not found complaint records regarding the superheat spec for their part which has been on the market for 20+ years.

Assuming the following:
This is a conversion from R12 to R134,
Both manufacturers stamp their TXV part with R134,
The aftermarket evaporator matches the OEM,
The new compressor (Sanden scroll type 4993, TRS090, 85.7cc displacement)
The original compressor (Sanden scroll type TR 70, 70cc displacement)

I have two scenarios that could point to an overall answer:

1) Assume the system would perform best with TXV superheat = 4.0 What will happen when a TXV with superheat 8.0 is used? Any pros?, Any cons? Would this affect the optimum charge weight?

2) Assume the system would perform best with TXV superheat = 8.0 What will happen when a TXV with superheat 4.0 is used? Any pros?, Any cons? Would this affect the optimum charge weight?

I realize that these TXVs can be adjusted, but not on an operating system, so that’s out of the question.

Two things come to mind: Will using a lower superheat TVX get us closer to possible condensation in the suction line and thus possible slugging of the compressor? Will using a higher superheat TVX reduce maximum cooling capacity and if so, what practical end results could we see?

Thanks in advance.

[JohnHere]

How about the original TXV...is it still serviceable? A TXV doesn't "care" whether it's R-12 or R-134a that's used.

[JohnHere]

The important point to remember about superheat is that you don't want any liquid refrigerant to enter the compressor after it exits the evaporator because any liquid will "slug" the compressor and most likely, damage or destroy it.

The refrigerant will be in a superheated state from the evaporator's exit to the condenser's entrance. Note that "superheated" doesn't necessarily mean warm or hot. Some superheat (latent heat) in a TXV system is desirable, therefore, to keep the refrigerant above its boiling point and in a gaseous state.

A TXV having a superheat of 4°F or 8°F won't make any difference as long as the refrigerant remains a gas as it travels through the compressor. So if you decide to replace your TXV, either one that you have mentioned above will work, IMHO.

[90efAACIF]

Thanks JohnHere.

The original TXV is completely plugged up at the end of the external equalization tube and the plug matter is hard as cement and a brownish color. In fact, the plug extended into the port on the output tube of the evaporator such that it was very hard to remove the tube from the evaporator.

I’m in agreement with your additional explanation of superheat. Your further comment,

The important point to remember about superheat is that you don't want any liquid refrigerant to enter the compressor after it exits the evaporator because any liquid will "slug" the compressor and most likely, damage or destroy it.

makes me wonder if there are scenarios where the refrigerant might start to condense in the suction line as it makes its way to the compressor suction port such as at an abrupt reduction in line diameter at fittings. In other words, loss of some superheat in the suction line would matter if it were greater than the value set by the TXV. I have to revisit the details of the proposed custom suction hose that replaces part of the original suction line used for use with the new compressor and post for your comment.

Also, for reasons of understanding, if the TVX superheat was much, much higher than 8°F, how would this be felt in system performance?

[JohnHere]

Also, for reasons of understanding, if the TVX superheat was much, much higher than 8°F, how would this be felt in system performance?

I'm not a MVAC engineer, but to answer your question, I believe that with a much higher TXV superheat, the evaporator will be warmer because the liquid refrigerant will boil off at some point before it reaches the evaporator's exit. The opposite situation would also be true. A lower TXV superheat would cause the liquid refrigerant to boil off closer to the evaporator's exit, resulting in a colder evaporator. In either scenario, only refrigerant vapor would return to the compressor, which of course is a good thing.

[90efAACIF]

I suspect I’m over analyzing at this point, (and wouldn’t mind being told that!) where I proposed:

makes me wonder if there are scenarios where the refrigerant might start to condense in the suction line as it makes its way to the compressor suction port such as at an abrupt reduction in line diameter at fittings. In other words, loss of some superheat in the suction line would matter if it were greater than the value set by the TXV. I have to revisit the details of the proposed custom suction hose that replaces part of the original suction line used for use with the new compressor.

What got me wondering is that the OEM suction path is as follows:

The hard line from the evaporator (about 32” long) has an I.D. ~ 0.52” which is essentially #10, 12.7mm I.D. That’s followed by a 12” long hose marked 14mm I.D. The fittings have short lengths of restrictions (0.425” I.D.) as well as expansions relative to the main I.D. That could break up laminar flow and (maybe?) result in some loss of superheat to the tube.

The proposed suction path only changes the hose section to #10 reduced barrier, thus matches the hard line I.D, with female o-ring beadlock fittings at each hose end and adds a #10 male insert o-ring to pad style adapter for the new compressor. My gut feeling is that superheat losses are insignificant for either OEM or proposed, but sometimes I have a hard time accepting my own gut feelings!

Some folks have cannibalized the pad (manifold?) fittings for the new compressor from hoses for the next gen civic. While that works, it adds clocking of the fittings to the natural bend of the hose, worst for the discharge line since both ends need to be clocked relative to each other. Here’s a pic of those adapters which reduce / eliminate the clocking requirements.

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[JohnHere]

makes me wonder if there are scenarios where the refrigerant might start to condense in the suction line as it makes its way to the compressor suction port such as at an abrupt reduction in line diameter at fittings.

I doubt it.

[90efAACIF]

Thanks John,

I mentioned that the TXV equalization tube was completely blocked with hard crud. I forgot to mention that in cleaning up the fitting end of the liquid line to the TXV that the old o-ring was also fused to the liquid line hard as a rock. After cleaning it up, I think that line end was corroded, possibly by galvanic reaction between the dissimilar metals of the line and TXV. The line itself has a rough surface that I think could cause leakage around the new o-ring even if try more herculean polishing efforts. Here's pics of before and after. Do you agree replacement makes the most sense?

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