A/C Receiver Dryer

[ODZKing]

The switch that is on the receiver dryer is the low pressure switch, is it not?
The parts book lits the same code then lists "low pressure" and "high pressure".
PN 3502016 which crosses on the NAPA site to TEM 207068.
This so-called :"complete kit" from Classic Auto Air is not so complete. No water valve, no hardware, no switch.

[Pete in NH]

Hi,

On an original R12 system the switch on the receiver-drier is a low pressure cut off switch that will turn off power to the compressor clutch if the system pressure falls below a certain point, 30 or 40 pounds I think.

On a R134A conversion there are high/low dual cutoff switches. 30 or 40 pounds on the low end and something over 300 on the high end. But, I believe these dual switches are then placed on the discharge side of the compressor, not on the Receiver drier. Are you working on a R134A conversion?

[charger Downunder]

I have just bought an engine upgrade kit off them to 134a in the instructions it says to reuse the old one, great if you have one none in the kit, i have ordered one switch from here and in the description it says.


Binary Switch very similar to O.E. located on Receiver Dryer. Will not allow compressor
to run when system maybe low in Freon and also shuts compressor off if discharge pressure
skyrockets because of an obstruction in system. Work with both Receiver Dryer
Numbers BPE6660 & BPE6661. Designed for use with R134 Freon Only and a must
change when retrofitting from R12 to R134 Freon.

http://www.bpeusa.com/BPEac_dryers.asp

[ODZKing]

Are you working on a R134A conversion?

Yes

[Pete in NH]

Okay on the R134A conversion. Looks like Charger  Downunder found the binary cut off switch that the kit supplier wants you to use. Are you installing A/C in a non A/C car with a complete kit, or are you converting a factory RV-2 compressor system?

Our friends at the EPA want a  high pressure cut off switch installed on R134A conversions because R134A runs at higher discharge pressures than R12. This is particularly true in systems using the old R12 serpentine condensers. R134A is not as efficient at heat transfer as R12 so under some conditions the compressor discharge pressure really takes off with the old R12 condenser. The EPA is concerned about releasing refrigerant if a hose lets go under those higher pressures and would like the compressor shut down before a hose blows. The better place for that high pressure cut off is right between the compressor discharge port and the condenser. But, that calls for some new plumbing to accommodate the switch. Placing it on the receiver drier is more convenient but I'm not sure it will accurately monitor the discharge pressure as well in the liquid return line. I should add that many R134A conversions are done without adding this high pressure cut off switch but it's a good safety feature to have and technically the EPA requires it.

[ODZKing]

Car technically has factory A/C so yes, converting.
According to Classic Auto Air, All I need to do is transfer my old switch to the new dryer.  Or they suggested I could eliminate it all together.
The other switch is on the firewall and was supplied.

[Pete in NH]

Sounds like a firewall forward conversion kit where you use the original evaporator under the dash but everything under the hood is new. If this is the case, you will have a new axial type compressor and hopefully a new parallel flow condenser along with a new R134A compatible receiver-drier. If you are using a newer type compressor, I would defiantly not eliminate the at least the low pressure cut off switch. Unlike the old Chrysler RV-2 compressor which contains its on oil pump lubrication system, the newer compressors depend on refrigerant flow to carry the oil around to lubricate the compressor. If for some reason the refrigerant level goes too low, you for sure want to turn off the clutch to the compressor drive or the compressor will quickly become ground up aluminum. Whether you use a low/high cut off switch I'll leave to you,but for sure use a low pressure cut off switch.