2.3L ('83-'97) Let me pick your brain with a vacuum leak/AC issue

[97ranger11]

Does anyone have a wiring and vacuum diagram for hvac?

Cliffs through post 4,
CLIFFS

• air sometimes only blows through defrost vents
• a.c went from working to working intermidently to not working at all
• when the ac would come on just before it stopped coming on at all, low side pressure would spike see https://youtube.com/shorts/FMTw_N00IUs?feature=share
• 2 years <1k miles on new compressor, condensor, accumulator, evap flush
• relay socket getting constant and trigger power, tried swapping relays
• both switches 14v in/out
• clutch coil not getting 12v

I'm thinking blend door actuator is not routing air through evaporator causing low side pressure to rise till switch disengages clutch. And a coincidink of a bad pressure switch.




97 2.3l ranger

So, I've traced all the heater related vacuum lines from the intake manifold to the dash and can't find any visual issues, however if I soak the area just to the passenger side of the EGR valve Idle bumps from 800rpm to 900-950rpm, so I imagine there is a small leak in that area.

So this truck has always had a rev hang. I just let it be, with all of the current issues I suspect it's vacuum related. A few months ago air started stopping coming out of the vents at random. It'd happen then fix itself repeat etc. I never checked but I assume it defaulted to defrost. That's got a lot worse recently, only it only happens when I have it set to heat (so when cold in morning). Haven't had it do it with the AC in a while.

Now the real problem, AC stopped working. Well now it doesn't work at all, before it worked some of the time gradually decreasing to none of the time. The one time I got gauges on it when it came on (recently that is) the low side pressure spiked up to 100+ psi before kicking off the compressor. High side didn't excede 150psi I don't think. The clutch coil isn't getting power, fuses are good, and I don't suspect wiring issues. A year ago it got a new compressor, condensor, orifice tube, accumulator, and a good flush and has been ice cold since. I don't suspect a leak. I immediately think pressure switch given everything I replaced, but can't help but wonder if it is vacuum related.

Thoughts?

Edit: thinking about it, I wonder if it is not diverting air over the evaporator causing the low side pressure spike? Doesn't explain why the compressor is no longer kicking on at all though.

 

[Shran]

I don't believe anything is vacuum operated in your AC system except for the flapper door inside the HVAC plenum (I believe anyway.)

I would highly suspect the low side pressure switch is faulty. IIRC it is supposed to kick on at about 40psi. If you are seeing 100psi on the low side, your gauges are either faulty or the system is grossly overcharged. Have you added any refrigerant?

 

[97ranger11]

I don't believe anything is vacuum operated in your AC system except for the flapper door inside the HVAC plenum (I believe anyway.)

I would highly suspect the low side pressure switch is faulty. IIRC it is supposed to kick on at about 40psi. If you are seeing 100psi on the low side, your gauges are either faulty or the system is grossly overcharged. Have you added any refrigerant?

The refrigerant level is good (haven't touched since the full a/c overhaul over year ago and when it works I get <40F vent temps) and I highly my gauges aren't bad. Forget the brand but they are the good ones (over $200) and only a year old and never had other issues with them. My thought is A/C kicks on but no airflow over the evaporator causes low side pressures to rise until the switch kicks it off. Regardless it's not even doing that now, I am getting zero power to the clutch coil. Resting pressure is roughly equal to or slightly under ambient temp in F.

I'm thinking maybe blend door actuator AND a pressure switch? Vacuum leak just a coincidink?

 

[Shran]

You should only see power at the clutch coil when the compressor is running (duh, I know) but power runs through the low pressure switch from the relay. When the low side pressure increases to a certain level, the switch will kick the compressor on and you will see a pressure drop. I would trace the wiring back from the switch and see if you have power there, at the relay, fuse panel, check your HVAC control panel for a faulty switch there too.

 

[97ranger11]

You should only see power at the clutch coil when the compressor is running (duh, I know) but power runs through the low pressure switch from the relay. When the low side pressure increases to a certain level, the switch will kick the compressor on and you will see a pressure drop. I would trace the wiring back from the switch and see if you have power there, at the relay, fuse panel, check your HVAC control panel for a faulty switch there too.

All the air coming out the defrost vent and/or air not getting routed to the evaporator would be the blend door/actuator, correct?

I am pretty sure it is not a electrical (switches aside) issue but will trace back to rule that out. Both high and low side switches have 14v going in and out of the pigtail. Is that normal to have both at the same voltage (i.e. no voltage drop/resistance) on a 2 wire switch?. Honestly I have no clue how the switches work, I was thinking they produced low voltage like an o2 sensor.


I have a vaccuum gauge coming, does anyone know what amount of vacuum I should have on the small lines used for heater controls/egr (red/green hoses and all hoses connected to them) power runs through the switch? Both or just one (one on accumulator and one before condensor on driver side I think?) I think the low side has 4 wires?. I know the switch creates voltage depending on the pressure like an o2 sensor (and obv will prevent compressor from cycling) but didnt know they had power going to them. Sounds like it essentially act as a relay trigger wire for the clutch coil? anyone have a wiring/vaccuum diagram for the hvac system? Here's. Clip of the ac gauges ~5s after turning the ac on from when it still would turn on. Didnt catch the low side spiking but when it starts dropping is when the clutch disengages. https://youtube.com/shorts/FMTw_N00IUs?feature=share

 

[Shran]

All the air coming out the defrost vent and/or air not getting routed to the evaporator would be the blend door/actuator, correct?

Probably, can't say for certain on your truck (majority of my experience is with '94 and older that have a different dash and AC controls.) My '07 F250 got stuck on defrost only but it ended up being a vacuum line popped off of the HVAC control panel - putting that back on fixed it.

The switches are nothing like an O2 sensor, those send a variable signal to the computer. AC pressure switches are just on or off. So for example on the low side, if the switch is set to trip at 40psi, it just closes the circuit and allows power to the compressor at and above 40psi. Below that the circuit is open and the compressor won't have power.