I'm restoring the A/C system in my '93 USDM FD. When I got the car, all it had A/C wise was the evaporator core and HVAC controls intact. All the HVAC wiring is good and appears unmolested. Based on the size & type of fittings on the evaporator core, I figured out my FD had a Denso system. I've sourced a good used Denso compressor, a Denso dryer bracket, and the hoses/fittings for the compressor. Since I'm running a single turbo, the OEM hard piping for the large Denso suction line to the evaporator core won't fit, so I'll be finishing off the A/C system with the biggest generic parallel flow condenser that will fit (12x24 inches), a generic dryer that fits into the Denso bracket & space avaiable, and building up custom hoses with new bead lock fittings and perhaps use some of those Vintage Air "U bend em" aluminum hard lines to make for a cleaner install.

Which brings me on to the questions on the pressure switch, as the FSM, electrical schematics (FSM section Z) and Body Electrical manuals all give conflicting info in regards to that switch....

Physically, the FSM shows the pressure switch plumbed into the dryer piping, but the Denso compressor I have sitting on my workbench clearly has a pressure switch physically attached to it, and its obviously wired in series with the clutch solenoid. This wiring arrangement jibes with the FSM electrical schematics (section Z), which only shows 1x NC pressure switch, wired in series with the clutch solenoid/coil. Nowhere in the FSM or any Mazda manual that I could find shows the switch physically located on the compressor, or a 2nd pressure switch that might be located elsewhere.

Another wrinkle is the Body Electric manual shows 2 different open/close pressure specs for the switch, depending on use of R12 or R134A. The specs are actually pretty close; the switch is basically closed for pressures between roughly 25psi to 350psi, and open when below/above that range (with some hysteresis at the switching thresholds).

So my questions are: (1) Is the pressure switch on my compressor THE one & only pressure switch the system needs? and (2) Would it be smart to simply get another trinary (i.e., high/low) pressure switch and wire it in series with the existing compressor pressure switch just in case the switch on the compressor only protects for low pressure conditions only? I can probably rig up a test to find the low pressure threshold/switch point on the compressor pressure switch, but there is no easy way to test for its high pressure threshold (if one exists) short of charging the system with refrigerant and running the system with gauges attached.

 

So my 4 Seasons reman compressor had a switch (and hole for a switch) in the front of it. The original compressor did not. The reman folks simply left it in to seal off the hole and trimmed the wires off.

Mine looked just like this: https://www.ebay.com/itm/Four-Season...75.c3#viTabs_0

Sucks that they are so expensive now! I got mine for $40 shipped.

These compressors (TV14) were used in a number of other cars (Subaru, Toyota,etc), so it seems some housings could be a bit different.

If you already have a pressure switch in the stock-ish location, then I would just wire it up like stock and leave the sensor in there as a plug.

Seems these random compressor switches are located on the suction side. The stock switch is located on the high side after the drier, so I wouldn't think they can be substituted for one-another.

There is also a thermo-switch on the top of the compressor... just to be clear we're not talking about this one right?

 

Here's a picture of the switch on my compressor, and a picture of the Denso part # tag on the back of it. I haven't taken a look at an exploded view diagram of this compressor's innards, but it looks like it could be tapped to see pressure on the high side. The only thermal switch I know of in the system is mounted on the evaporator core, and it senses when the core is approaching freezing point, to prevent condensation from icing up on it and blocking air flow.



Switch is that triangular thing on top with blue connector

Hard to see here, but part # is TV14C

 

Oh yeah that's just the thermo switch. Used to monitor outlet port temp. Do you have the service highlights PDF? They talk about it in there I think. Anyways... that is normal and you should leave it connected.

 

Ok, interesting - found it in the service highlights. That's the only Mazda document that shows that switch. Which means the FSM electrical schematics (section Z) are wrong, as they don't call this one out at all in the electrical schematics. And I suspect they have the pressure switch wired wrong in the FSM section Z, which shows it on the switched side of the A/C relay (where the thermo switch should be shown instead). I assume it's connected in series with the the coil side of the A/C relay, but the FSM doesn't show a switch there. Anyway, my question is answered, I'll need to plumb in a trinary pressure switch into the dryer line to kill the compressor if pressures go above or below the high & low thresholds, respectively.