Hell167

Im trying to get the ac working on my fd with microtech ecu. so i searched and found that i can simply jump 1L(yellow/black) with 1E(grey/red). so i did a quick test with my test light before i jump them. The 1L when given ground does activate the ac clutch and i can hear it click.. however the 1E wire doesn't give any neg when pressed. the light on the button turns on. Ive tried with the car on, the car running, and i cant seem to get a signal from the ecu harness. Ive taken the center console off and check the harness, everything is plugged in, but i cant find the grey/red wire.

does the grey/red wire change colors at the center console a/c button? if so which wire would it be? if i can get the signal from the button i can run a new wire to 1L whether the signal from the button is pos or neg, i can just wire in a relay if needed.

could i be not getting a signal because theres nothing in the system?

what else can i check?

Gen2n3

iTrader: (1)

Hell167,

Could you explain a few things so I (and others) may offer sound advice?

First, what are your references? Provide a link to the thread you found that suggested this jumper wire. Second, what manuals did you use to understand the electrical flow? Did you use the BEM (Body Electrical Troubleshooting Manual) and WDM (Wiring Diagram Manual)? Third, what connector are you using to jumper Pins 1L and 1E - is that connector at the ECU? Fourth, are you connecting a wire between Pins 1L and 1E on the loom (harness) side of the ECU? Lastly, what year is your FD?

Hell167

sorry, im working on a 94 FD. and im using the 94BEM as reference in section G. 1L and 1E refers to ecu harness 1. (both these wires were not used by the microtech lt10s)\

after looking closely, im guessing the pressure switch isn't allowing the neg signal from getting through to 1E, so i guess i wont really be able to test it till i get a vacuum pulled and refilled.

Gen2n3

iTrader: (1)

Hell167,

Thank you for the input. You can also use the WDM especially when referencing the ECU. However, the BEM has key troubleshooting tips for the AC system.

It is important to understand that Pins 1L and 1E from the ECU harness are ground signals. One (Pin 1E) controls the Refrigerant Pressure Switch, thermoswitch, and Coolant Fan Relay #1. The reason why the ECU controls this ground signal is to prevent the AC from running under high load/high RPM conditions. The other (Pin 1L) is an input to the ECU that comes from the AC Relay. In order for your AC system to properly work with an aftermarket ECU, you would need to connect Pin 1E and 1L to chassis ground. You can jumper these 2 pins together but you MUST tie the jumper wire to ground.

CAUTION: Damage to the AC System and/or engine may result when running the AC at high RPM/engine load.

Now, you must also consider the system may not operate if the refrigerant is under-charged. That is the function of the Refrigerant Pressure Switch. Did you convert to R-134a or using R-12? Is your AC system empty or have a leak? The system would work once any/all leaks are fixed and it can maintain pressure.

Take a look at Diagram Gb in the WDM (Pg Z-70). The GY/R wire you mentioned from Pin 1E only goes to the Refrigerant Pressure Switch at Connector G-07. It changes color when routed to the thermoswitch and again changes color when split to the Heater Control Unit (amplifier) and to the Coolant Fan Relay #1.

The A/C Switch looks like it is integrated into the Heater Control Unit (controller). I would not recommend bypassing the switch from the Refrig. Pressure Switch and thermoswitch for safety reasons. You can severely damage the AC system when it is run without refrigerant.

Did I answer your questions? Keep the forum posted on your progress.

Hell167

thanks, figured it went to the pressure switch first. i will have to get the ac system pressure tested and charged if needed. im not too sure exactly what refrigerant is in there right now as i recently purchased the vehicle.

if i tie 1L jumped wth 1E together to ground, wouldn't that just ground 1L and activate the ac compressor clutch once acc is given? not sure what grounding 1E will accomplish. i thought the job of 1E was to send out the ground signal to ecu, and ecu sends ground signal (when conditions are right) to 1L so the clutch would engage when the ac button was pressed.

Gen2n3

iTrader: (1)

Hell167,

The AC System would still be triggered by the AC Switch. Keep in mind that the AC Relay (Pin 1L) is an input to the ECU. It will energize when the Blower switch is set to any speed (1-4) and when the AC Switch is engaged. Pin 1E sends a ground output from the ECU to the Refrig Pressure Switch and then to one side of the AC switch. The magnetic clutch on the AC Compressor shouldn't engage until the Refrig. Pressure Switch senses the proper amount of pressure and completes the circuit. This is why that switch is a fail-safe for the AC system.

If you really want to be careful then you could wire up an additional switch to emulate the ECU. Connect Pins 1E and 1L to one end of this additional switch and the other to chassis ground. When you want to run the AC then you would need to activate this switch first and then press the AC Switch.

Does this answer your questions?

Hell167

If thats the case and both 1E and 1L require ground then which wire send the signal(when you press the ac button) to the ecu telling it to send the neg signal to 1E and 1L?

sorry, now im really confused. I thought the ac button was 1E.

Gen2n3

iTrader: (1)

Hell167,

I owe you an apology for misleading you. I read solely from the schematic without diving deeper into the theory of operation. I based the input and output of the circuit upon current flow alone which led to this confusion. After reading the AC system in the BEM and the FSM (Section F), and comparing this info with the schematics from the WDM I believe the below description should resolve any confusion.

NOTE: If you have difficulties reading the table from Diagram B-1, then reference the Terminal Voltage List in Section F of the FSM, Pg F-152. This table is easier to read and also contains possible causes for abnormal indications.

In the WDM, Pg Z-36 lists the ECU Pins with their corresponding descriptions. Pin 1E is connected to the AC Sensor (aka AC Switch). It is listed as an input to the ECU. When the AC Switch is on, the voltage at Pin 1E should be less than +3V. When the switch is off, the voltage at Pin 1E is B+ (+12V or more when car is running off alternator). In order to see this voltage, certain conditions must be met. Specifically, the Blower Switch must be on (set to any fan speed) and the Ignition Switch must be on. Note that the engine does not need to run because this only addresses the electrical portion of the AC System.Now, Pin 1L on this table is connected to the A/C Relay and it is listed as an output from the ECU. You would see specific voltages at Pin 1L based upon the following conditions:

NOTE: The engine must be running in addition to placing the A/C Switch and Blower Switch to their ON positions.

1. During Engine Cranking: B+ (+12V)
2. When engine is at idle: Less than +1V
3. During acceleration: B+ (+12V)

Next, refer to the FSM, Section F, Pg F-140. This discusses the A/C Cut-off function, which is an internal logic function of the ECU. According to the FSM, “An A/C cut-off system [is] used to improve idle smoothness immediately after starting the engine and to improve acceleration performance.”

Examine the diagram on Pg F-140 and you will see many inputs to the ECU along the left edge of the diagram. All of these inputs feed into a logic gate that is simply listed as “Determination of A/C Cut Off”. This output is sent through a transistor before it reaches the A/C Relay and Magnetic Clutch. This transistor acts as a high-speed switch that will allow current to flow from the A/C Relay when the above conditions are met. Please note, this transistor is tied to ground.

Still using this diagram on Pg F-140, let’s focus on the A/C relay. When the Ignition switch is closed, battery power flows through the relay but cannot go past Pin 1L. This is part 1 of the confusion because the transistor inside the ECU controls the A/C Relay. This also explains why you would normally see B+ voltage at Pin 1L during engine cranking or when accelerating.

NOTE: The A/C system will disengage when the throttle valve is fully opened. Refer to FSM, Pg F-142, Inspection of Acceleration cut-off, Step 4.

When the engine is under normal load or at idle the transistor switches on. This allows current to flow from the Battery, through the A/C Relay, into the ECU at Pin 1L, through the transistor, and finally reaches ground. This is part 2 of the confusion because the A/C Schematic in the WDM uses arrows that indicate current flow. More about this error in the next three paragraphs. Now that the transistor allows current flow to ground. This will close the open contacts of the A/C Relay. These open contacts are connected to the Magnetic Clutch on the A/C Compressor. Once closed, the compressor turns on and pumps refrigerant through the system thus providing cold air into the cabin.

Next, look at Diagram Ga for cross-ref point 35. On Pg Z-68, at the far left of the page you should see cross-ref #35. The arrow points down and indicates where the signal is going, which in this case is the ECU. Backtrack this line line through the A/C Relay and it will go through the CIGAR Fuse and then to the Ignition Switch’s ACC position. Underneath the Ignition Switch, you will see the wire color B/Y with an arrow pointing left. This left pointing arrow indicates the direction of current flow. Given these indicators, I believed this line to be an input to the ECU. This was part 3 of the confusion, which was an incorrect interpretation on my behalf.

Now, look at Diagram Gb for cross-ref point 34. On Pg. Z-70, at the far left of the page you should see cross-ref #34. The arrow pointing towards the Refrig Pressure Switch indicates the direction of current flow. Current flows from the ECU at Pin 1E into the Refrig. Pressure Switch, feeds directly into the thermoswitch, then hits a tie point. This tie point creates a parallel path for the signal to travel. In one direction the current flows from the Coolant Fan Relay #1. We shall disregard the path from the Coolant Fan Relay for now. The second direction for current flow enters the Heater Control Unit Amplifier then runs into the Heater Control Unit Controller at the A/C Sensor (A/C Switch). Once the A/C Switch is closed, the current will then flow out of the Heater Control Unit Amplifier then output at cross-ref #99.

Cross-ref #99 goes back to Diagram Ga at the right edge of the diagram. It feeds in between the Blower (Fan) Switch and the Fan Speed Resistor network. The current flow hits a tie point and then travels down to Position 1 of the Fan Speed Switch (when set to 1). Current would also flow through the other Fan Speed Positions via the Resistor network and then to ground. This resistor network is also connected to the negative side of the Blower Motor. The number of resistors selected by the Fan Speed Switch will determine how fast the Blower Motor would run. Part 4 of the confusion ultimately came when I followed this current flow to ground. I concluded this path from the ECU was an output that flowed through the A/C Switch and into the Fan Speed Switch.

So, the big question remains: how to best wire your car for A/C? The original solution to jumper the input Pin 1E to the output Pin 1L should work. If you heard relays click and the LED on the A/C switch lit up then it sounds like you have electrical power to the A/C system. You would still have to ensure the system is properly charged with refrigerant in order to test.

CAUTION: Damage to the AC System and/or engine may result when running the AC at high RPM/engine load without the A/C cut-off protection circuit.

When possible, would you provide the link to the jumper wire thread you initially referenced?

Again, my apologies for creating the confusion between the input and output of the A/C system. Thank you for keeping me honest!

Hell167

Thank you for the extremely detailed write up!