Automotive Air Conditioning Information Forum

Detroit, that is really good to hear.
A lot of superheat would suggest the TXV is underfeeding? Correct? It is a 1.5 ton valve, same as we always use. Have tried 3 of them.

There is plenty of cold air at the vents, see above for temps at the 4 vents.
If I dial the thermostatic switch back from max, the clutch will cycle, but when it re-engages, the pressure is right back to 15.
There is no frosting at all, just cold pipes.

You would think that at 15 psi, the evap core would be a solid block of ice.
The condenser outlet is quite warm, and the drier is quite warm. The pipes in and out of the evap are cold and seem like the same temp by hand.
The system behaves like no other I have worked on. But if oil will return, I will lay my concerns aside.

When it warms up some today, I am gonna take readings on 2 other vehicles here with the exact same components

I thank everyone for their comments

As a reality check, I just checked the pressures on 2 vintage vehicles we did, a 1931 and a 1947.
Both have the EXACT same components we have on this '59 Cadillac

Car 1 30/200
car 2 30/230

did not measure vent temp but ice cold as usual, prolly 40°

I agree with what DetroitAC said about oil return. In GM POA-valve systems, for instance, as the POA throttles down, oil return is also throttled (reduced)...hence the reason for a separate oil-return line that bypasses the POA. The system in question doesn't have a POA, though, so the oil is carried back to the compressor with the suction gas (superheated or not) at whatever pressure it happens to be at the time. So in this instance, I don't believe that oil return is a problem.

Have you verified that there is not an OT installed in the line between the R/D and TXV causng an additional restriction?

John, by now you prolly have the same headache I have thinking about this. I appreciate your ideas.
There is no OT; we buy lengths of hose and use our own crimper to make our own hoses.
It has been suggested that the suction line has a flap in it (delamination defect) thus that it will flush fine but partially restrict flow under suction.

We may never know.
I am gonna change out the TXV, the evap, and the suction line and see what happens.
Tim sent me a really really nice compressor (Japanese) at a good price and I don't want it to fail. As far as the evap, we have gotten bad parts from Old Air before. I will be sourcing a different brand. This is gonna take some time, and I will post back.

An internally delaminating hose is something else I thought of after I posted, and it is another remote possibility. Only other thing I can think of is the evaporator.

MVAC is often not easy to diagnose and repair, as has been said many times before. Let us know the results after you change-out the parts you mentioned.

With barrier hose, it would be pretty odd that it collapses. Not like the old days.

tbirdtbird wrote: ↑Sun Sep 19, 2021 10:15 am As a reality check, I just checked the pressures on 2 vintage vehicles we did, a 1931 and a 1947.
Both have the EXACT same components we have on this '59 Cadillac

Car 1 30/200
car 2 30/230

did not measure vent temp but ice cold as usual, prolly 40°

Is the evaporator airflow the same for all these 3 vehicles, or does the problem child have less?

All 3 evaps are identical.
I wish I had a way to measure airflow but I don't

Indeed! Not a drop of oil to be found
Thus my concern for proper oil return