user 84948

So this may be why manually grounding the E24 terminal on the PCM didn't start the compressor and fans?

user 84948

The manual calls for a tools call the MPCS Short Connector (Part 07WAZ -0010100) that plugs into the MCU. Can the same thing be achieved by just using a jumper cable with alligator clips to short that circuit?

ezone

That's what I'm thinking.

Jumper wire, yes. I think the cavity has 3 terminals in it? Jump the outer pins. T1-T3.

The special tool (if it's the one I'm thinking of) is a 3 wire connector shell that fits the cavity. with the two outer terminals bridged together.

user 84948

Well....it looks like we are closer to the finish line. With the little bit of testing I did this afternoon, it looks like we are close to calling it the MICU. Let me know what you think.


Here are my test results:

Terminal Q3 (driver’s door switch to MICU)
Red lead on Q3 connector wire-side and black lead on negative battery terminal:
1. Ignition in OFF position and door open: 9 on Ohms 200 setting. 0 volts.
2. Ignition in ON position and door open: 12 on Ohms 200 setting. 0 volts.
3. Ignition in OFF position and door closed: 1 (infinite) on Ohms 200 setting. 11 volts.
4. Ignition in ON position and door closed: 1 (infinite) on Ohms 200 setting. 11 volts.
Note: This would confirm that when door is opened, a signal is being transmitted to the MICU

Terminal X5 (ignition key switch to MICU)
Red lead on X5 connector wire-side and black lead on negative battery terminal:
1. Ignition in OFF position (key inserted): 4 on Ohms 200 setting. 0 volts.
2. Ignition in OFF position (key out): 1 (infinite) on Ohms 200 setting. 11.3 volts.
3. Ignition in ON position (key inserted): 7.5 on Ohms 200 setting. 0 volts.
Note: This would confirm that when key is inserted, a signal is being transmitted to the MICU

Terminal O7 (MICU to ceiling spotlight/dome light)
Red lead on O7 connector wire-side and black lead negative battery terminal:
1. Ignition in OFF position and door closed: 1 (infinite) on Ohms 200 setting. 12.3 volts.
2. Ignition in OFF position and door open: 1 (infinite) on Ohms 200 setting. 12.3 volts.
3. Ignition in ON position and door closed: 1 (infinite) on Ohms 200 setting. 12.2 volts.
3. Ignition in ON position and door closed: 1 (infinite) on Ohms 200 setting. 12.3 volts.
Note: This would confirm that there is a communication problem between Q3 and O7….pointing towards problem with the MICU

Grounding terminal connector O7 turns spotlight on (confirming circuit from O7 to ceiling light works)

I tried running the self test on the MICU, found the T1 and T3 terminals (interesting because there are only two terminals), tried shorting them with ignition in ON position. Nothing happened with the dome lights (supposed to flash the DTC code). I checked for continuity between T1 & T3 terminals (what the books said to do if no codes flashed). No continuity between T1 & T3 terminals.

ezone

Preliminary: Check fuse #9 in the engine compartment fusebox and fuse #10 in the dash fusebox.


Did you get to the point of:



Turn key on
Insert tool (jumper wire) and after 5 seconds the ceiling light comes on and blinks bla bla bla



Result=NO ceiling light?
Go to step (7 in my info),


Check for continuity between terminal 4 of fuse box connector J and body ground. (J4 is connected to T1 in the diag socket)



Is there continuity?
Yes: Replace fusebox.
No: Repair ground G301....This one is behind the washer tank out in front of the wheel.


If it won't enter mode 1 and the fuses and wiring are intact, the MICU must be bad.


If you can find "Multiplex control unit input test" it should have a boatload of individual wire checks at the fuse box if you want to pursue more, but it sounds like you need a fusebox.

user 84948

Here are the steps listed in my book:

Part 1
1. Check the No. 9 (10 A) fuse in the under - hood fuse/relay box and the No. 10 (7.5 A) fuse in the under-dash fuse/relay box.
Are the fuses OK?
YES – Go to step 2.
NO – Find and repair the cause of the blown fuse.
MY RESULT: Good fuses, continuing to step 2

Part 2
2. Remove the dashboard lower cover (see page 20- 75).
3. Turn the ignition switch ON (II).
4. Check self-diagnosis function Mode 1 for a
diagnostic trouble code (DTC) by connecting the special tool (A) to the multiplex control inspection connector (B). After about 5 seconds, the spotlight and ceiling light should come on then blink 0.2 second. This means that you are in Mode 1 of the self-diagnosis function.

Part 3
5. If there is a DTC, it will blink, pause, then repeat the DTC as long as the ignition switch is ON (II).
Is there a repeating DTC?
YES – Count the blinks, then go to step 8.
NO – See if the SCS circuit is working properly. Go to step
6.
MY RESULT: no blinking occurred at all, even to let me know I was in self test Mode 1...continuing to step 6

Part 4
6. Check for continuity between the inspection connector T1 and T3 terminals.
Is there continuity?
YES – Go to step 7.
NO – Faulty under-dash fuse/relay box, replace it and
recheck for DTCs.
MY RESULT: no continuity


Part 5
7. Check for continuity between the connector J of under - dash fuse/relay box No. 4 terminal and body ground.
Is there continuity?
YES – Go to step 9.
NO – Repair the open in the wire and recheck for DTC's.
MY RESULT: yes I have continuity (0.4 on Ohms 200 setting)



It does sound like a bad MICU, and I think we have done enough testing to make an educated guess (most education I've ever gotten ). I have ordered the part from Honda (I figured it wouldn't be smart to go used or aftermarket), should be ready to pickup in the morning.

ezone

Sounds good to me. Good luck!

user 84948

So good news. Swapped out the MICU last night. AC compressor kicks on, key chimer works, dome light with door switch works, and brake light went off. Great! AC still doesn't blow cold (I had a feeling there would be something else too), hooked it up to the gauges, turned on the AC (full fan speed & recirculation) and did a reading (after warming up the car).

Low Pressure Port: 5
High Pressure Port: 105

It is about 85 degrees with 63% humidity right now.

Since both the high and the low port have lower pressure than they should, does that mean it is low on freon? If so, how can I check if the system is leaking? I don't want to be wasting money pouring freon in if it is just leaking right out.

ezone

Sounds like a low charge to me.
You don't know anything about the car, there could be several reasons it may be low....just one of which is a leak.
Someone could have tried to mess with the freon in attempt to get it working with no success, and that could leave it quite undercharged.


The fact that it has a partial charge and you've had the car (what, a month now?) it can't be a huge leak or it would be flat empty.

Look for telltale oil+dirt stains around pipe connection points and hose crimp points....

Add some UV dye and add freon to get it cooling good, then see how long it lasts.

If it leaks out later on and blows warm again, you should have some UV evidence to look for with a blacklight.

user 84948

Yup, bought the car last Thursday. I'll check for the oil stains. Do I just use manifold gauges (with yellow tube) to fill refrigerant until at correct PSI on low side?

I don't need to do a vacuum at this point right?

ezone

If you are only trying to top up a system you don't necessarily need to discharge or vacuum (evacuate) it. You CAN carefully add more freon til its working better.

If charging by weight (using a machine) then you'd recover, evacuate, and recharge.
If the system had been opened up you would want to evacuate it before charging


There's far more to it than just the low side. The high side is important too.

You actually have manifold gauge set and (a can of freon) to put in it?? You aren't a normal DIYer LOL.


Easy way would be to add a little freon, wait a bit let it stabilize, check pressures on both high and low sides, vent temperatures (and I also feel pipe temps if doing it this way).
Add a little more, check pressures and temps.
Repeat until it's cooling good.
Make sure pressures aren't too high.

System freon capacity is small....A couple ounces over or under spec and performance can suffer.
It's way too easy to put in too much, and performance suffers greatly if it's over or under charged.

The pressures are a huge variable, you would almost need to check pressure-temp charts to see if yours is reaching an expected range based on actual conditions.


-------------

Get the car out of direct sun. The Civic system is small and really is undersized for the car, direct sun can overpower the system (add heat faster than the AC can remove it) especially if the car is a dark color, and newer cars are worse. LOL

I can check temps two ways.....
Performance test:
Open all doors and windows, turn AC on and use throttle prop to keep engine @1500 RPM....run for 10 minutes to stabilize the AC system, put fast acting digital thermometers in the center vents and blower intake (open the glovebox wide to find it by the cabin filters)...max AC, recirc on, fan full blast...

Looking for about a 20 degree F or greater drop between blower air inlet and dash vent temps, and this temp difference can vary a lot depending on humidity levels. (High humidity means less drop, low humidity means more temp drop.)

Example
If it's 85* ambient and 60% humidity, test set up as above
got 80* at the blower intake
60* from the vents or less
30 psi low side (20-30 range)
200 psi high side (190-250 range)
that's within reason.


Then roll up windows and seal up the cabin and see what the dash vent temps do. If they drop a lot you're doin good.
If it gets cold enough to have the compressor cycling on-off-on-off it's real good.
If it's real hot out it may not be strong enough to cycle sitting still, but may cycle while driving at highway speed.
I like my digital thermometer to be sensitive and fast enough to watch the temps go up and down a few degrees as the compressor cycles on and off.