Aviator857

I've wired my ac using the diagram in post 35 here.
https://www.thirdgen.org/forums/ltx-lsx/527269-1989-5-3-t56.html#post4248157

However I'm thinking I really should add the cycling/low pressure switch from the 89 to this setup.

Who has it it wired like this? Does your clutch cycle on/off with the AC on?

If you added the low pressure switch is it in series with the high pressure switch or between the controls and the pcm?

scooter

iTrader: (11)

You wired it using the 4th gen pressure switch? Using this diagram?

Aviator857

Yes that wiring with the 4th gen pressure switch/sensor. It may not be cycling as it's too cold to build enough pressure. It's pulling it from 58 outside temp to 28 vent temp so it's working. Low side pressure is 25-30 psi and high side is 150-200 psi with it running. But the clutch stays on when I select AC, it never cycles on/off. It does turn off if I turn off AC.

I see that the 4th gen sensor does both high/low switching. But I'm thinking I should add the thirdgen low switch to protect on for low freon situation.

scooter

iTrader: (11)

I don't think the low pressure switch is going to gain you anything since it does both pressures. Maybe your switch is bad or your reference is wrong? When I built my harness, I used a dedicated 5V reference since there were lots of unused ones deleting the emissions stuff, there was no need to share one.

I would have an AC person look at it before you make changes, you may be putting in work for an issue that won't be fixed by that anyway.

Also, I am running R12 in mine with the 4th gen pressure switch, not sure if you're running 134 or what, but the pressures are supposed to be different

Aviator857

R134, the AC wiring is more or less "stock" as I'm running the 4th gen fuse box so the relay is in 4thgen location.

Which wire in the diagram is the 5v reference?

My gut says it's simply not warm enough to build enough pressure to get it to cycle, I have 24oz of R134.

The AC I put in my Toyota has a temp switch also to keep it from freezing up. But I ended up with way too much r134 in it because I charged it when it was cold.

​​​​​i also put a ohm meter on the low side switch on the dryer ( currently not wired ) and it stayed closed so it was also not switching.

Do you know what pressure the 4th gen opens/closes on?

Also I have the 4th gen sensor on the high pressure hard line, that's correct right.

All parts except that switch is brand new.

Aviator857

Scooter do you know if the 2000 compressor is a variable or fixed compressor? if its a variable compressor then I think everything is working as it should be. If I idle up the car to say 3000 rpm it rises some then falls down again to nominal pressures with the clutch never turning off so... I'm thinking its variable. I guess I've only ever worked on fixed displacement AC systems so I was expecting the clutch to turn on and off to maintain the pressure.

scooter

iTrader: (11)

I don't know. I have spoken with a guy at Classic Auto Air and he said a lot of the newer ones are variable, mid 90's or something.

Aviator857

FWIW turns out it is variable displacement and it is designed to run continuously when on. I'm pretty sure everything is working as it should now.

scooter

iTrader: (11)

So did you make any changes?

I think my evaporator actually freezes up in summer, it's kind of annoying. I should have done mine like the 3rd gen with the high and low switches instead of the 4th gen dual switch with the R12

Aviator857

No changes. Also I've monitored the low pressure switch that is still on the dryer but not wired in and it isn't hitting the cut off pressure either. Since the compressor from the 2000 varies its displacement to maintain a certain running pressure it never hits this pressure. I suppose that in certain temps it could exceed the compressors ability to compensate and would but I can't test until its oh 99 with 100% humidity here in summer So far I've only tested with the temp between 35 and 60 outside temp.

I have gauges and they show correct pressures high and low, even at higher RPMs and its dropping the temps on the inside. Really my only concern is freezing up the evaporator. If that happens the only thing I can think of is to add a temp probe to it since it seems the thirdgen or 4th gen doesn't have one. I'm sure I can find a car that does that acts as a simple off switch if air temp is below freezing. If I have to add a temp probe I'll wire it in inline with the wire going from the control panel to the pcm.

scooter

iTrader: (11)

OK, just wondered