Hi all,
I'm researching bringing my 1LE pretty close to a factory AC install. All wiring inside the cabin for HVAC control is there with the exception of the evaporator temperature sensor (acquiring a used one, hard to find). Everything in the engine bay is custom, and I've started deleting.

I have a single big coolant fan assembly with a single relay. I'm trying to find in the theory of when the coolant fan kicks on during HVAC compressor operation.

I've been studying the 8A diagrams and have read quite a bit of the 1B sections of the 1994 service manual and haven't seemed to find it yet. I've found bits and pieces that suggest the pressure switch controls the fan via PCM when the HVAC compressor is in operation.

Does an AC equipped car require a 2 coolant fan setup, or is the single big fan sufficient?

What I want to happen is a more factory type of install where when HVAC command is given, the PCM commands the coolant fan to activate. I believe this is done through pressure switch signal voltage, but I haven't found the wiring from the PCM to the single cooling fan relay that is responsible for energizing the relay during HVAC operation.

Hoping for some guidance and clarification of how the coolant fan kicks on when using the HVAC and associated wiring/relay(s).

-Eric

 

I just have to find the wiring from the PCM to the coolant fan relay.

In some diagrams I see multiple coolant fan relays, in others only 1. This is where I'm struggling based on my current configuration of a single coolant fan assembly, rather than a 2 fan setup.

 

Apparently I need a 2 fan assembly and associated relay(s) and wiring.

I'm looking for the schematics now for those, as I'll have to install/integrate them into the system for proper PCM control of the HVAC.

 

Inside of my fuse box. Gonna look for one that has AC. According to the diagram I need the AC Compressor Relay, another Fan Relay, and the A/C Cruise 20A circuits wired in.

 

Not all 94’s used a three relay system (both fans on low speed/both fans on high speed). The early production 94’s used a two relay system (Fan 1/Fan 2). Shoebox’s PCM wiring diagrams show the two different version:

http://shbox.com/1/1995_pcm6.jpg

Actually the 95 manual shouldn’t include that version of the diagram, since it only applies to 1994.

 

My 1LE was a late build in May 28, 1994. That explains why my fuse box lid shows a coolant fan relay #3. I'm assuming late model production coolant fan control with AC operation commanded by the PCM is superior to early production that was controlled by PCM but operation was different. I'll be wiring/integrating the system coolant fans to late production.

 

Oh that helps a lot. Surfing through the factory service manual is a bit painful without knowing all the appropriate nomenclature, but I'm getting there.

I'll be running a harness from the PCM to the engine fuse panel for the 3 coolant fan relays, AC compressor relay, and AC/Cruise Fuse, and power distribution a S165.

The other 2 harnesses will be from the pressure switch to PCM, and evaporator temperature sensor switch to PCM (and their associated splice and shared ground point).

A single power wire from Connector 230 will route to PCM for HVAC request I believe.

I haven't found it for the 5.7, but I did for the 3.4 in the 1994 svcman, the PCM pinout assignments table. Of course I'm going to be looking for those, and the appropriate schematics for the cooling fan relays, ac compressor relay, and AC/Cruise fuse location and associated wiring. 8A-64 has been my starting point, and referencing a few others.

 

I think you may be over estimating the part that A/C pressure plays in “controlling” the fans. It’s basically an “on/off” control. The PCM will not start the A/C compressor if pressure is not adequate. If pressure is adequate the PCM starts the compressor, and turns the fans on at low speeds. That's it. When the A/C is not operating, it’s fans low speed on at 226°F and high speed at 235°F. If A/C is operating, low speed is on, and high speed at 235°F.

The risk of running a single fan, and turning it on when A/C is on is that you would see increased, unnecessary heat removal in the radiator, but the thermostat goes into operation to prevent the engine from running too cool.

 

I read both early and late model operations from the PCM, only thing I'm concerned with will be terminating them correctly via the appropriate schematics for the 3 relay system. I'll be picking up the wire (appropriately colored), pins/contacts , crimp tool, and relays on the next days off cycle.

 

Are you sure the 1LE harness isn't the same as the A/C vehicle harness, just not using all the connectors for the A/C? Might not have been unique non-A/C harness, given the relatively few that were built. When you installed the single fan did you rip out the fan control wiring, except for what ever relay controls that fan?

 

There isn't any AC wiring in the engine bay forward of the pass through grommet on the passenger side firewall under the PCM.

There's only wiring for what's shown in the fuse block.
The single large fan assembly I have is factory, as is the wiring to the motor, relay, fuse etc.

From what I was saying earlier, I'll run all the PCM->Relays harnessing, as well as the pressure switch and evaporator temperature sensor. The only weak point now I'm currently researching is the AC/Cruise splice point going back to ignition, and a couple other splices.

I'll use the PCM pinout/ table for 1994, and run everything from there to the fuse block (fans, clutch relay), compressor, pressure sensor, evaporator temperature sensor/probe.

Everything in the cabin is normal HVAC control system with a rear defogger fused at the I/P fuse panel.

 

"the evaporator temperature sensor (acquiring a used one, hard to find"
For what this is worth, I have found a sensor that is about the same specs to make for a substitute. This is just a simple component and not a full sensor module. But it can be a start to replacing the original one since it has the same resistance at room temp and is the same type (NTC termistor).
https://www.digikey.com/en/products/...-400D9/1190948

 

Hi Gary,

If the specs of the device are the same as what's OEM, it should communicate fine with the PCM for HVAC Compressor control. Would be interesting to test it, although access isn't that great having to pull the heater core and glove box.

I'm assuming you've compared the form, fit, function of the two sensors?

-Eric

 

Good info on the temp sensor. Few months back someone was looking for a replacement, and I looked into pulling the one out of my Formula with deleted A/C. Problem was I sold the car, but I figured the new owner would let me pull it. Then I read the factory service manual directions for removing it, said you need to pull the heater core, and I thought that would be asking too much of the new owner, and probably beyond the physical limitations of my senior citizen status. I suspect that’s why 4th Gen owners doing an A/C delete just unplug it and move on, without realizing they could sell it for a decent price.

 

Haha. You give me way too much credit ;-) At this point all I have is a very preliminary idea for how to replace the original sensor. The device I posted is about the right size for the evaporator but I have not tested it over temperature ranges yet. Of course all it has to do is provide the same voltage level at about 32F as the original sensor; since that is the goal, to keep the AC system from freezing damp air in the evaporator,

Fred is absolutely right about the FSM saying you have to remove the heater core first. However (and do not quote me on this) I have heard of people cutting a hole (next to the PCM) in the AC box in the engine compartment and getting very limited access to the evaporator core. You could push the sensor into the core and run wires from it inside to the connector. Again, this is all hearsay, but may be technically possible.