tdaver

I apologize if this information is somewhere else but I simply couldn't find it. I am doing the AC conversion from R12 to R134a on my 1990 PU DLX 4WD 22RE. I have all of the 1995 parts but I cannot figure out what to do about the high pressure switch (in the evaporator). The connector on the 1995 (88645-04040) looks different than the 1990. As I understand, the cutoff points are different for the two refrigerants.

Any suggestions? I can leave the R12 switch but it doesn't have the correct pressure switch points or, use the 1995 switch and try to replace the connector. Help?

scope103

I don't know if the there are different pressure switch points (could be; R12 and R134a are subtly different), but I can tell you that R134a works fine in a '94. https://www.yotatech.com/forums/f116...-r134a-284801/

If you know what the switch points are for a 1995, you can compare them to this FSM: https://web.archive.org/web/20110205...19pressure.pdf

tdaver

Thanks SCOPE103! I'll check this out. My progress: The switch points for each of the switches is written on the side. The older style (1990-R12) has 2.1 kg/cm2 (30 psi) for the low switch point and 29 (412 psi) for the high switch point The 1995 R134a unit has 2.0 kg/cm2 (28 psi) as the low and 32 (455 psi) as the high. So the only real difference is that the R134a version switches at higher pressure. Looking at a temperature/pressure chart for R134a, 412 psi is about 185F where 455 psi is about 195F. The low switch point for R134a is 32F so that the compressor shuts off before the evaporator freezes. Probably OK to keep the 1990 switch.

ClydeDuncan

Replying for the updates.

tdaver

Thanks everyone for helping this noobie. After more research, it seems the 2.0/32 kg/cm2 (28/455 psi) are the standard numbers for R134a. This seems to be true of all R134a switches, not just Yodas. The upper limit on the R12 switch is 412 psi which could probably work, but I don't want to open the evaporator later to change it later. I am planning on using the R134a version, but now I'm looking for the right connector. Does anyone know how to figure out the connector for this, or anything in the truck?