Pressure Switch Part Numbers

[Rickf]

I am converting my 1990 GMT400 from r12 to 134a. Does anyone have the part numbers for the pressure switches of the r4 compressor and dryer?
Thanks,
Rick

 

[tsr2185]

I am converting my 1990 GMT400 from r12 to 134a. Does anyone have the part numbers for the pressure switches of the r4 compressor and dryer?
Thanks,
Rick

low pressure switch for r134 = DORMAN 904625

Yours has a high pressure switch? My 1991 only has a relief valve on the compressor instead of a high pressure switch. I bought it already converted to r134a.

 

[Rickf]

My local FLAPS comes up with a switch for r12, nothing specifies 134a. The r12 switch has 6551828 stamped on it, will it work on a retrofit r4 compressor using 134a?

Thanks for the dorman number.

 

[PlayingWithTBI]

My 1991 only has a relief valve on the compressor instead of a high pressure switch.

Yeah the earlier R12 systems used a 1 wire HP switch, which is NLA. GM designed it to close the recirc door, when you get high pressure, to help bring it down. Remember R12 ran lower pressures. On my 88, I wired this HP switch in series with the LP Cycling Switch so I have protection against HP blow outs etc.

https://www.oreillyauto.com/detail/c/murray-climate-control/murray-climate-control-2-terminal-pressure-switch/mry0/35961/v/a/3009/automotive-truck-1988-chevrolet-c1500-pickup-rwd?q=high+pressure+switch&pos=0

I also installed a relay for my clutch to get full battery voltage to it. Here's my schematic, modifications are identified in blue...

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Edit: Oops wrong drawing, this is the one I meant to post - not enough coffee yet.