IRCM in depth

[5.8capri]

My fan my 92 is not working and i have ordered, but not recieved my EVTM. I have checked for input pwr and that is fine. I tried grounding pin 14, and a relay clicks, but no power to the fan. I am using a multimeter to check at the terminals where fan pwr leaves the IRCM. So i decided to open up the IRCM and found out that if i manually ground the relay that is next to the big white resistor, i get pwr for the fan, however that is not the relay that comes on if i ground pin 14.???? There are 4 relays, i know 1 for the fuel pump, one for the fan and one for the A/C clutch, but what is the 4th one for? can anyone tell me what the activating inputs are for the different relays? Are they all grounds? Also should i have VRPWR at the plug for the ect with the key on? I have 0vdc as it is. Any help would be appreciated before i melt my motor. thanks

 

[89 black SHO mtx]

ok i'm not sure where your problem is. but here is a little tid bit of info that might help you. the last time i had a rad fan failure i was at home (with out most of my tools) all i had was a multimeter. it showed power but the fan wouldn't run. what i'm getting at is that a multimeter won't show you if you have a bad fusible link. try checking with a test light it makes the connection draw amps nto just read power>

 

[Mr Anonymous]

If you search under CCRM, I seem to recall someone posting a complete pin-out recently that might help you test it.

 

[sdpatt]

The fourth relay is the wide open throttle A/C compressor cut-out relay.

Pin 14 is the ignition switch to ignition coil and will not in itself actuate the fan relay.

To see of you are getting power to the fan motor, turn the climate control to MAX A/C with the engine on and test for voltage at the electrical connector to the fan (which you had unplugged before starting the engine). If no voltage at the connector, the ICM is suspect.

If you have power to the fan motor, the most common mode of failure of the fan motor is that the brushes wear out. Search on sources for the motor or the brushes if that is the case.

 

[5.8capri]

I know the fan is not the problem. it works fine when hooked to the battery. I am getting good power into the IRCM, and when i manually ground the one relay, the fan will come on. I have tried turning on the A/C, but to no avail. Thanks for the inputs and ideas so far. Does anyone know what voltage I should read at the ECT? Shouldn't it be around 5vdc?

 

[sdpatt]

Let me say this again. Press the MAX A/C button on the climate control. If there is no voltage at the fan output from the ICRM, the ICRM is faulty. If there is voltage at the output of the ICRM, the ECT is the fauly component. You are trying to make this more difficult than it is

 

[projectSHO89]

what i'm getting at is that a multimeter won't show you if you have a bad fusible link. try checking with a test light it makes the connection draw amps nto just read power>

Don't mean to slam you, but....

This must be some kind of misconception on your part and a misunderstanding or lack of knowledge in basic electricity (voltage, amperage, power, resistance, etc.) and its measurements.

The meter will show if you have an open fusible link, you will read no voltage at all. A test light will draw a few hundred milliamps max which will be of no consequence in testing this circuit. FWIW, I've survived as a professional electroncs technicion for 27 years and as a shadetree mechanic for many of those without ever owning or using a test lamp in an automobile. The meter is adequate for everything. Of course, you do need to know how it is to be used.

Back to the original problem... 92 SHO

Pins 1 & 2 supply the power for the fan going INTO the IRCM. Pins 3 & 4 are the OUTPUTS of the relay that feed to the fan motor itself. Pin 14 (92-93) is the EDF* (Electro-Drive Fan -LOW) signal. This signal is generated by the ECA under specified conditions and is an active LOW (ground) signal. Grounding this pin will, in a properly operating system, energize the proper relay withing the IRCM and will turn on the fan motor. The ignition key must, of course, be in the RUN position to perform these tests, otherwise there will be no power to the coil of the EDF relay. That power is supplied by the EEC POWER relay which is energized whenever the ignition switch is in the RUN or START position.

Ignore all the other stuff for a moment and go test that. First check for VPWR at pins 1 and 2. If so, then ground pin 14 and see if the relay energizes and the fan comes on. No power at pins 1 & 2 means a supply issue, notably a 50A fuse in the engine compartment fuse block labeled COOLING FAN.

The fourth relay is the wide open throttle A/C compressor cut-out relay.

To clarify...

The schematic (92/93) that I am consulting shows four electro-mechanical relays and one solid state relay. The E-M relays are as follows: EEC PWR, HIGH FP. LOW FP, & EDF. It also shows that the dual speed FP function is not inplemented as such, both relays are simply in parallel The AC CLUTCH is controlled by the solid state relay (labeled A/C WAC RELAY). The control circuitry for this relay includes the input from the cycling switch (pin 21) and an EEC input named WAC (pin 22) that performs the wide open throttle cutout function.

An interesting observation last week on my 89. The AC was not working due to a failed (open) cycling switch. I could turn the AC selector to normal or MAX AC and the cooling fan would not come on as I expected it to. As soon as I replaced that switch and made the system work again, the fan behaved exactly as expected. My hunch is that the EEC is waiting to see a small drop in RPMs via PIP and a recovery via the ISC before energizing the EDF. My guess is that this strategy is there to avoid slamming the system with the simultaneous loads of the compressor and the electrical load from the fan kicking in.

Steve

<small>[ March 25, 2003, 09:31 AM: Message edited by: projectSHO89 ]</small>

 

[sdpatt]

Thanks for the functional description. That was good.