Does the AC dryer pressure switch have a valve under it that will let me change it without bleeding the system down?

It does not appear possible.

1994 Isuzu Truck Trooper (4 Door) V6-3165cc 3.2L SOHC (6VD1)

Vehicle Level (http://library.alldatapro.com/alldata/LIB~C20649~R0~OD~N/0/41746445/56622022/56622029/56622474/34853741) http://library.alldatapro.com/images/a_003366.gif Heating and Air Conditioning (http://library.alldatapro.com/alldata/LIB~C20649~R0~OD~N/0/41746445/56622022/56622029/56622474/34853741/34865608) http://library.alldatapro.com/images/a_003366.gif Receiver Dryer (http://library.alldatapro.com/alldata/LIB~C20649~R0~OD~N/0/41746445/56622022/56622029/56622474/34853741/34865608/56273486) http://library.alldatapro.com/images/arrow1.gif Service and Repair (http://library.alldatapro.com/alldata/LIB~C20649~R0~OD~N/0/41746445/56622022/56622029/56622474/34853741/34865608/56273486/14455124) http://library.alldatapro.com/images/arrow2.gifhttp://library.alldatapro.com/images/blnk_spc.gifService and RepairRECEIVER/DRIER

http://library.alldatapro.com/alldata/LIB~C20649~R0~OB0~P3R0H~N/0/41746445/56622022/56622029/56622474/34853741/34865608/56273486/14455124/91256472/78722321

Preparation:
Disconnect the battery ground cable.
Discharge and recover refrigerant (http://library.alldatapro.com/alldata/LIB~C20649~R0~OD~N/0/41746445/56622022/56622029/56622474/34853741/34865608/56273766).



Radiator grille
Pressure switch connector
Refrigerant line
When removing the line connected part, the connecting part should immediately be plugged or capped to prevent foreign matter from being mixed into the line.
Bracket bolt
Receiver/drier
Loosen the bolt, then, using care not to touch or bend the refrigerant line, carefully pull out the receiver/drier.INSTALLATION
To install, follow the removal steps in the reverse order, noting the following points:


If installing a new receiver/drier, be sure to add 30 cc (1.0 fl.oz.) of new compressor oil to a new one.
Put the receiver/drier in the bracket, and connect with the refrigerant line. Check that no excessive force is imposed on the line. Fasten the bracket bolt to the receiver/drier.
Tighten the line to the specified torque. Torque: N.m (lb.in) = 6 (52)
0-rings cannot be reused. Always replace with new ones.
Be sure to apply new compressor oil to the 0-rings when connecting refrigerant line.

Does your service manual have the directions for replacing just the pressure switch. I do not need to replace the dryer because the AC is working just fine.

Thanks for your time
nujac

Hi, I checked and could find no reference to how the pressure switch is attached to the dryer . I do know that on most GM vehicles that use the pressure switch there is a schraeder valve in the fitting that the switch screws on to. I just don't have any personal experience with the isuzu. Are you getting no clutch engagement at all, and that is why you want to change it, or is there another reason?
This switch appears to be just an under and overpressure switch to keep the system from operating at extremes, as when low on refrigerant or extremely high hi side pressures.

Normal pressures are in the range as follows for the switch in your system:



A/C Pressure Switch (http://library.alldatapro.com/alldata/LIB~C20649~R0~OD~N/0/41746445/56622022/56622029/56622474/34853741/34865608/56191162)
Air conditioning system pressure below 196±20 kPa (28 ±3 psi) indicates a loss of refrigerant (http://library.alldatapro.com/alldata/LIB~C20649~R0~OD~N/0/41746445/56622022/56622029/56622474/34853741/34865608/56273766) or refrigerant oil (http://library.alldatapro.com/alldata/LIB~C20649~R0~OD~N/0/41746445/56622022/56622029/56622474/34853741/34865608/72634452). The A/C pressure switch opens with low system pressure to prevent compressor damage. Also, with system pressure above 2648±198 kPa (384±28 psi) , the A/C pressure switch opens to prevent compressor damage.

The pressure switch stays open because the guy that had the car before me had a ground on the pressure switch wire and put too large of a fuse in it. The switch is now burned in the open position. I have jumped the switch with a wire and all of my high and low side pressures are fine and the AC cools really well.

Thanks for your time
nujac