Getting the AC running on my 1996 XLT

[sebastian323]

I have a 1996 Truck with factory AC, so I will use this thread to take some notes on how I get the system operational again and ask for advice

The first step has been to inspect the various components of the system to see what works and what does not. I will divide this into a few section

AC system - sensors, compressor, leaks, fuses, pressure sensors

Interior Electronics - blend door, HVAC control unit
*Blend door - the blend door motor makes an electronic motor noise when I turn the knob, but I cannot seem to get cool air from the system. I only seem to be able to get warm air, so I assume the motor is good (no weird clicking noises) and the blend door is bad.
*HVAC control unit - the unit sends voltage to the blend door and causes the blend motor to move so it seems to be working.

Vacuum controls - heater core bypass valve, HVAC directional controls - all seems to be fully functional
* The heater core bypass valve works - the air blows cooler when I have max AC on (but still stuck from the blend door)
*The max AC switch does close the vent allowing only internal air to be recirculated
*The HVAC directional controls indeed do change where the air comes out from


Diagrams:

Blend door pinout 1996 Ranger:

bk - black - ground
g/y - gray - power from fuse 10 in cabin fuse box
other 3 wires - potentiometer pinout

 

[Vindictus]

This is a good read https://www.therangerstation.com/tech_library/Resurrecting_Your_Ford_Ranger_Air_Conditioning.shtml

 

[RonD]

AC works by compressing a liquid to a high pressure then slowly releasing that pressure
High pressure causes heat, releasing that pressure causes cooling

AC system power is pretty basic in 1996

AC on(12v out)---pressure switch---pressure switch---relay----AC clutch coil--ground

So with AC on the AC clutch gets 12volts IF pressure switches are both closed
If pressure gets too low compressor will burn out, if pressure gets too high hoses will blow out
Compressor usually cycles off when pressure is high enough so AC can cool cab using reserve pressure

The relay is a 5 pin, so when its OFF it passes the 12v to the clutch
Its called the WOT(wide open throttle) relay, computer will activate this relay, turning off AC, when driver wants FULL POWER to pass or ??
So as long as the relay is not corroded it should pass the 12v all the time



Blend Door Actuator was always an issue in 1995 and up Rangers and other Ford models
Electric motor that would just quit working one day
Not part of AC system it just moves a flap that diverts air from the fan either thru the heater core(HOT) or around the heater core(COLD) or anywhere in between, Temp control to "blend" the incoming air
Generally if it ain't working you need a new actualtor
AC has no Temp control, its either on or off, so Temp knob has no connection to AC, just FYI


1995 and up Rangers do use Vacuum "motors" on the Vent control system, i.e. defrost, panel, floor
Defrost is the Default for the vacuum motors, so no vacuum = defrost

MAX AC has an added vacuum control, in MAX AC setting vacuum is sent to Fresh Air Vent "motor", closing it so the fan pulls in already cooled air from inside that cab to recirculate
Good to use on dusty roads or whenever you want to keep outside air outside, lol
MAX AC will also close the heater by-pass valve in the engine bay, this can add a few degrees of extra cooling as the heater core cools down
But the main cooling effect for MAX AC is closing the Fresh Air Vent, i.e. trying to cool down 90deg air from the outside or trying to cool down 80deg air from the cab is self explanatory, lol

 

[sebastian323]

AC system power is pretty basic in 1996

Blend Door Actuator was always an issue in 1995 and up Rangers and other Ford models
Electric motor that would just quit working one day
Not part of AC system it just moves a flap that diverts air from the fan either thru the heater core(HOT) or around the heater core(COLD) or anywhere in between, Temp control to "blend" the incoming air
Generally if it ain't working you need a new actualtor
AC has no Temp control, its either on or off, so Temp knob has no connection to AC, just FYI

I checked all the vacuum controls and they are good. The blend motor does whirr when turning the knob (no clicking noise) but I do not think the door is acutally moving because I still keep getting warm air when the fan is blowing.

I am going to test continuity through the two switches. My compressor will kick on manually when shorted to the battery, but will not run otherwise. I assume there is a leak or the system is low, or the switch is out. Per my best guess, the system has not been functioning since at least 2020.

 

[RonD]

Bummer about hearing the actuator motor but no movement of the door
Could be the door sleeve broke, which is very hard to replace

But keep a good thought, lol

Google: A look Inside the Ford Blend Door Motor and how to fix the temperature control

The actuator has a small electric motor that turns a worm gear, this turns two sets of gears that rotates a square shaft that is inside the sleeve of the blend door
Broken sleeve can look like this: https://www.therangerstation.com/Magazine/Summer2009/heater-core/Top_Axle_View.JPG

Very rare to have the sleeve break, 99% of the time the actuator is the issue stripped gear or bad motor

With actuator removed and broken sleeve
Google: DIY Fix Blend Door on 96'-00' Ford Ranger

You can cut the front of heater box and bend down a flap you made to reach inside to set the blend door as you want it, for summer and winter until you get time to do the full repair
You don't want to move the blend door manually with actuator attached or you WILL break the sleeve

 

[sebastian323]

I will take off the blend door motor (mine is held on without screws on my 1996 XLT) and I will slide my phone in to take a picture of the sleeve for the blend door flap.

Also, when I press on the low pressure side r134a port with a small screwdriver, I do have a some pressure and it does make a hissing noise. Does that mean the system is leak free ? From what I recall though, other systems had more pressure.

 

[RonD]

Yes, if its been 3 years or so and it still has some pressure there is a very good chance it has no leaks
Try refilling but use refrigerant that has a UV Dye mixed in, in case there is a leak in the future you can find it, High side pressure gets up to 300psi on a warm day, 95+degF

Wire connector for actuator is usually long enough so you can plug it back in when its out, turn key on and rotate Temp Knob, see whats not working

 

[sebastian323]

I filled the low side pressure port with 75-100ish PSI of r134a (with system off) and it seems to be holding. The compressor still will not come on. I am guessing it is safe to force start my compressor by powering the clutch straight from the battery? Does it sound like my low pressure switch might be out ?

"If there is enough static pressure (the pressure in the system when the A/C is not running) which is over 75 psi, and the electromagnetic clutch is working, when you turn on the A/C, the clutch will engage the compressor which pressurizes the Refrigerant gas. "

Can i also check to see if I get 12 volts to one of the connectors on the pressure switch to see if the controls in the cabin are providing the signal

 

[franklin2]

The standard procedure for filling is to unplug the low pressure switch and put a short jumper wire across the terminals. This will keep the compressor running so it can help suck the refrigerant out of the can.

If the system is low, the compressor will pump the low side dry very quickly. That is why you need to jump the low pressure switch out.

Make sure when filling, turn the blower fan wide open and if you turn the lever to max, make sure you roll down both windows. You need to keep warm air flowing over the evap coil to get the proper pressure readings. If you let the evap coil get too cold, the low side pressure will not build up and you will end up overfilling it.

 

[sebastian323]

recently something unusual has been happening when I attempt to turn the air conditioning system on. I can hear the clutch engaging, but every time the clutch engages, the engine begins to suffer from a hunting idle. After about two seconds the clutch turns off again and the idle goes back to normal. Two or three seconds later the clutch engages again and the hunting idle returns, and this repeats itself as long as the AC is attempting to turn on. I believe the compressor itself is having issues, and that is why each time it is engaged, it ends up causing the engine to run improperly.

 

[Mechrick]

High pressure causes heat, releasing that pressure causes cooling

I'll expand that a bit.

Refrigeration systems work by utilizing the energy transfer during the state change from liquid to gas (and gas back to liquid). The condenser's purpose is to change refrigerant from a (hot) gas back to a (relatively hot) liquid. The evaporator's purpose is to change the (relatively hot) liquid back to a gas. During this state change, heat is shed by the condenser and absorbed by the evaporator.

Interestingly enough, the temperature at the inlet and outlet of the condenser doesn't change drastically, typically only about 15 degrees Fahrenheit. Temp change at the inlet and outlet of saturated evaporators (as used in accumulator systems) is even less. The big temperature changes happen in the compressor and orifice tube (or expansion valve).

This is important because condenser function in R134a systems is critical to good system performance. By monitoring the condenser pressure and condenser outlet temperature it's possible to determine if it's doing it's job properly, by referencing a pressure/temperature chart for the refrigerant used. Example below. The goal is to have condenser outlet temperature lower than what the refrigerant chart specifies at the outlet temperature measured.

For example, in the chart referenced below, at the maximum temperature in the chart of 262.9 psi, the refrigerant is liquid at outlet temps below 150 degrees and gas above 150 degrees.

https://www.arkema.com/files/live/s...ls/forane-134a-pressure-temperature-chart.pdf

 

[franklin2]

recently something unusual has been happening when I attempt to turn the air conditioning system on. I can hear the clutch engaging, but every time the clutch engages, the engine begins to suffer from a hunting idle. After about two seconds the clutch turns off again and the idle goes back to normal. Two or three seconds later the clutch engages again and the hunting idle returns, and this repeats itself as long as the AC is attempting to turn on. I believe the compressor itself is having issues, and that is why each time it is engaged, it ends up causing the engine to run improperly.

Your idle air control valve is supposed to compensate for the extra compressor load. You might need to clean it and the throttle body and see if that helps it. Don't panic after you clean everything, it may not want to idle correctly until you take it on a couple of drives.