tobyj17

HI everyone, new member here with a tech question. What I've got is an A/c issue on my 02 civic.

Here's what happened and what I did: Discharge line rubbed through on one of the cooling fans. when the a/c was running. Of course the pressure dropped and the system shut down. It was late in the a/c season, so I just waited til this summer to fix it. Replaced the discharge line and the receiver/dryer and the condenser (damaged from animal hit). I vacuumed out the system for 10 mins, leak checked, and then charged with 18 oz. of refrigerant. BUT.. I still have no A/C. I have a lot of experience in electrical and AC..but all in heavy truck applications.

Here's what it does:

I have battery voltage going to the compressor. I read somewhere that if you ground out the blue/wht wire the clutch will engage. And..it does.. but it barely engages and slips. I also checked the pressure switch on the drier, and i have continuity though that. But, I'm not real familiar with automotive applications... where should be the next place I start to check?

Thanks in advance everyone.

fcm

Is your Civic a hatch?

You say you have power to the compressor, is that before or after the thermal protector on the compressor?

By the sounds of it either the voltage is low going to the compressor clutch coil, [after the thermal protector] preventing proper clutch engagement or he clutch coil is weak or the clutch itself is worn out.

To trip the clutch, jump the clutch relay.

Also FYI a 10 min vacuum on a system that has been open, [hole in line] is not near long enough, 45min is min., 1hr would be better.

Did you put oil into the system when you replaced the filter, condenser and line? 94

tobyj17

It's a four door LX model. I measured the voltage at the three wire plug that plugs into the compressor harness. I haven't checked the thermal switch yet..is it possible that it would only partially fail?

Also, yes I did add oil, I added two ounces. It was hard to tell how much was lost, but it wasn't much. Also, I figured I should have vacuumed it down longer..but it was in the mid 90's and just wanted it to work. Additionally, the compressor turns pretty free on it's own..you can spin it easily by hand.

jdmh22eg2

my GUESS would be either bad clutch or coil as said above. i would tend lean towards a coil as the comp has power and clutch worked fine until line rubbed through.

tobyj17

I was hoping it wasn't the clutch..but if it is then it is...Is that replaceable on these? I know most aren't.

Also, it doesn't try to engage at all with the controls on the dash. could ths be related?

fcm

Yes, the thermal switch can fail, the contacts in the switch can burn leading to high resistance resulting in low current to clutch coil.

Have you tried jumping the A/C clutch relay yet, it can narrow down the problem a lot?

There are a number of reasons the HVAC control head, [A/C switch] does not turn the A/C on, starting with the obvious, a bad switch to the most common, low refrigerant charge.

The A/C switch supplies a ground, that it gets from the blower speed switch, [blower must be on one of the speeds] that ground goes through the A/C thermostat, that monitors the evaporators temperature, [that may be bad or has no power] the output of the A/C themostat, [a ground] goes to the condensor relay turning on the condensor fan, it also goes to the A/C pressure switch, from the A/C pressure switch, [if A/C refrigerant pressure is within limits] it goes to the ECU/ECM, the ECU/ECM supplies the A/C "request", [suppling a gound to the A/C clutch relays coil, the relay inturns supplies the power to the clutch coil, that is why jumping the A/C clutch relay will point you in the right direction, or at the very least elliminate a number of possibilities.

BTW, A/C in cars/trucks is the same, in fact all A/C systems are the same with the exception of control functions and refrigerant used, all cars and trucks, [systems using an engine driven A/C compressor are pritty much the same other then the mentioned differances.

The A/C systems in "modern" cars are far more complicated then they need to be, [control wise], all you need is an on/off switch for a request signal, [it can supply power or ground] run that through an A/C themostat to cycle the compressor, [preventing evaoprator freeze up] then through an A/C pressure switch, [to allow operation only if pressure is within limits then to a clutch relay and condensor fan relay, that is it, the ECU/CM is not needed. 94

tobyj17

Thanks for the info. I found that the thermal switch on the compressor was bad however that's only part of the problem. For testing purposes I bypassed it. I tried jumping the relay, and still no clutch engagement. I also ran a diagnostic on the hvac controls and it didn't come up with anything. I have continuity through the pressure switch too.

fcm

Did you check to see if you had power at the relay?

Did you jump the correct terminals on the relay?

Just looked up the wiring diagram for the 02 Civic LX, and in Hondas great wisdom the output of the A/C clutch relay does not go through the thermo protector like on earlier models.

It is blue lead, [most likely aground] out of HVAC control head to the pressure switch, then a red lead out of pressure switch to the thermo protector, then a blue/white lead out of the thermo protector to he under dash fuse box, [multiplex control unit] then a yellow "communication" lead, [SEFMJ] from the MCU to the ECU/ECM, then a red lead, [ground] from the ECU/ECM to the A/C clutch relay.

Looks like even Honda is on the lets over engineer this as much as we possibly can band wagon.

I would start by seeing what you get at the blue lead when you turn the A/C on and off, then see if you have that output on the red lead at the pressure switch, move to the read at the thermo switch, then the blue/white output of the thermo switch and finally what you get at the blue/white input to the multiplex controller.

Then make sure you jump the proper terminals on the A/C clutch relay, that will be the terminal that has 12V+ on it at all times, [ign. on or off] and the terminal that is kiddy corner from it, [you do not need the ign. switch on to do the jump].

If the clutch does not engage, the clutch coil is bad or there is a connection problem between the relay and the clutch coil, test the lead going to the coil when jumping the relay, if you have power, the coil is the problem. 94

tobyj17

Okay so a quick update. Been working long hours so I haven't had time to look at it much... But, here's some more info:

When I jumped the relay I have no clicking. I tried the terminal with the power at all times to all three of the others. Nothing. I tried do check continuity with my meter from the relay terminals (all of them) to the blue/white wire going to the clutch and didn't get anything but open. Now, my big question is, in the wires on the bottom of the fuse box..which one goes from the relay to the clutch? Because I couldn't find a blue/white wire coming out of it...and in order to trace the wire to see if it's bad or if it's the multiplex unit, I'd like to start there and work my way to the clutch.

fcm

First, jumping power, [hot at all times terminal at relay plug] to all three other terminals was not a good idea, to the clutch terminal is no problem, to the 12V+ ign. terminal, [hot in run and start] is not a problem, however putting 12V+ to the control terminal, [ground from multiplex control unit] was not a good idea.

I do not know if the MCUs A/C request output circuit is diode protected, and feeding 12V+ into a ground out circuit can damage that circuit.


The output from the A/C clutch relay is a blue/red, not blue/white, the blue/white is the output of the thermo protector to the MCU.

Please fallow my directions exactly, "Then make sure you jump the proper terminals on the A/C clutch relay, that will be the terminal that has 12V+ on it at all times, [ign. on or off] and the terminal that is kiddy corner from it"

If you want to test the clutch, unplug it and supply power to it directly, use a jumper from the batt. 94

tobyj17

Alright. I jumped the relay with the ignition off and the A/C clutch clicks... so we've got that side of it working. Also, the relay is good.

fcm

Now look for A/C request, there will be a second 12V+ pin in the relay socket when you turn on the ign., [one side of relays coil] the kiddy corner one from it is A/C request trigger from the ECU/ECM to the relay, [red lead], turn on ign./start engine and turn on the A/C and test for a ground at that terminal, most likely there is not one.

Leave everything on and find and jump the A/C pressure switch, does compressor turn on, do you get cold air from vents?

If so the switch is bad, if still no cold air, refrigerant charge is low.

If jumping the pressure switch does not turn on the compressor, jump/bypass the thermo switch, if compressor turns on, replace the thermo switch, if still no A/C, my guess is the Multipex Control Unit is bad, you will need a scanner to test it. 94

tobyj17

I'll check for an a/c request.

The rest i have checked already. The thermo switch was bad (open) so just for testing purposes I bypassed it. I plan to replace it..along with the compressor simply because of the car's age and miles (240k)

I have continuity through the pressure switch (less than 1 ohm of resistance). when I ground out the red or blue wires the compressor turns on and I have cold air. Also, the cooling fans turn on.

I'll see if i can get ahold of a good scanner. I think we have one from matco at work..Either that or i'll just replace it. I'll keep you posted on my findings. Thanks!

fcm

GL. 94