[windswept4]

The radiator fan does not activate automatically as the engine coolant temp rises to the boiling point causing the engine including the temp guage to show all the symptoms of overheating. I can bring the engine temp down by simply turning on the A/C switch, which effectively is a manual switch that turns on not only the A/C but also the radiator cooling fan. This proves that the radiator cooling fan motor actually works fine and can be manually controlled on or off. This also tells me that the relay to the fan appears to be working (at least the relay that is activated by the A/C "on" switch). The radiator cooling fan will also come on when I disconnect the electrical harness to the coolant temperature sensor (CTS). I am told that when disconnecting the CTS with the result that the fan begins to operate is proof that the fan and the CCRM are in good operating order. Is this true? I believe it's proof that the fan is good, but not necessarily proof that the CCRM is in good operating order. I tested the 2-wire CTS (coolant temperature sensor) (NOT the single wire temperature sensor that goes to the temp guage on the dashboard) by measuring the resistance when dipping the sensor into 200 degree water. Within 5 seconds the resistance of the CTS dropped from around 30,000 ohms at room temp to near 0 ohms as its temperature rose.

Is my problem in the CCRM? or the PCM? I did buy a replacement CCRM (same part number) off a junker at the Pull-a-Part for about $10. No assurance that the replacement didnt have the exact same problem, but it did not bring the cooling fan back to life in the overheating range. I'm not sure where my problem is. Any help in this regard is appreciated.

[Dominick]

Did you check out your cooling fan control and the wiring leading to it.
Everco/Cooling Fan Control

For your 1994 Ford Taurus 3.0L EFI 6cyl

Price:
$129.99

[windswept4]

Is that the same as the CCRM?......here is a pin diagram of the 3.8L (mine is the 3.0L). I replaced it with another used one, with the same result as the existing CCRM. This is the electrical harness located right under the cowling above the radiator near the hood latch. I might need to check certain pins under certain operating conditions to see what's what and what is not what. Any ideas?

http://www.taurusclub.com/forum/atta...m_38l_1994.gif

[Poppy]

Here is a wiring diagram for a '95 which should be the same.
My guess is that you have a crappy connection in the connector to the CTS, giving a higher resistance reading thereby not causing the PCM to trigger the CCRM.

In response to your PM to me, Yes you can create a set of jumper wires to act as a breakout box for testing purposes, if you can't back probe the CCRM.
HowTo Check a Relay

[Boghog]

Originally Posted by Poppy

Here is a wiring diagram for a '95 which should be the same. My guess is that you have a crappy connection in the connector to the CTS, giving a higher resistance reading thereby not causing the PCM to trigger the CCRM. In response to your PM to me, Yes you can create a set of jumper wires to act as a breakout box for testing purposes, if you can't back probe the CCRM. HowTo Check a Relay

I usually try not to guess. If the resistance was to high from the sensor,it would be telling the PCM that the engine was COLD and other other features would also be issues, IE high idle rich mixture,no EGR causing engine to ping and so forth.If you tested the sensor and got the correct readings,which they sound correct,start looking at the signals comming from the PCM to the CCRM.The probability of you having 2 bad CCRM's with the same problem are remote.I would focus on the PCM signals.

[Poppy]

Originally Posted by Boghog

I usually try not to guess. If the resistance was to high from the sensor,it would be telling the PCM that the engine was COLD and other other features would also be issues, IE high idle rich mixture,no EGR causing engine to ping and so forth.If you tested the sensor and got the correct readings,which they sound correct,start looking at the signals comming from the PCM to the CCRM.The probability of you having 2 bad CCRM's with the same problem are remote.I would focus on the PCM signals.

You make a number of good points BUT... we are not living in a world of absolutes.

Quote:

I tested the 2-wire CTS (coolant temperature sensor) (NOT the single wire temperature sensor that goes to the temp guage on the dashboard) by measuring the resistance when dipping the sensor into 200 degree water. Within 5 seconds the resistance of the CTS dropped from around 30,000 ohms at room temp to near 0 ohms as its temperature rose.

What if there was 5,000 ohms resistance in the connector? So the PCM would get a range of 35,000 ohms to 5,000 ohms, instead of 30,000 - 0 ohms. With a minimum of 5,000 ohms, the PCM may think that the temp, never got over 180 degrees, (and it would not turn on the fan/s) yet that would be the normal operating temp and there would be no fast idle, or ignition ping.

While I made up the numbers, because I have no idea how many ohms represent what temperature, but I think that it explains my reasoning.

[Dominick]

A breakdown of relays in the CCRM

[Poppy]

If you look at the diagram I posted above, there is a connector C104 that is another location that could add resistance in the circuit, that as I explained above COULD cause the PCM to get false readings. Here is it's location.

[windswept4]

Thanks everyone for your suggestions, pics & advice. I'll look into that entire fan circuit (low and high speed) further. I'll also try to back probe some of the specific terminals around the Coolant Temperature Sensor Harness and around the CCRM. I'll also try to find a chart showing the designed resistance of the CTS at different temperatures to make sure that the resistance displayed is within manuf tolerances.

You guys are great at finding problems. Keep up the good work.

[windswept4]

I thought you might get some mileage out of this text of technical specs for many models, years and sensors

[Poppy]

This chart didn't make sense to me until I realized that the temps were in Celcius. I added the F conversions and it makes more sense to me now.
According to this chart, your initial resistance reading should have been 3,000 ohms, not 30,000 ohms at room temp. But since there is a geometric relationship to the temp and resistance, that may be acceptable, I really don't know.

However this chart further supports my thought that resistance in the connections may be the culprit. IF you look at the chart and add as little as 250 ohms resistance to each of the temps how will it change the info given to the PCM?
At 68 and 104 F it will make no difference.
At 140F the PCM will think it is about 135F
At 176F (normal operating temp, the fans won't be on yet) the PCM will think that it is 140F and the fans will not be turned on.
At 190F and above the PCM will think that it is 176F and won't turn the fans on.

[Poppy]

Another way of looking at it is that the PCM must see a resistance of less than 250 ohms before it will turn the cooling fan on. That includes the sum of any resistance within the sensor itself, and any in the connections.

[windswept4]

thanks poppy for the feedback. I'm going to carefully check the terminals of the coolant temp sensor and I will run a bench test of the resistance of my cts as I heat up a pan of water to see how closely the resistance matches the specs as listed on the chart. I'll report back the results later this week.

[Poppy]

windswept4, sometimes just the act of disconnecting and then reconnecting terminals is enough to clean them. Since you disconnected the CTS, have you tested to see if it is working normally again? I imagine that you are not using the [van] car or are running it with the AC on, or CTS disconnected.

[windswept4]

I did re-connect the harness to the CTS and have been using the sedan with and without the A/C depending on
1. How hot it is inside the cabin (when hot, i turn on the A/C)
2. If the dash board coolant temp guage shows the water temp creeping up into the red, I will turn on the A/C to manually start the radiator fan motor. Within a minute the water temp will begin to fall, once the radiator fan begins to suck air through the radiator.

Thanks for the suggestion.

[mark v]

Good thing about this image as it looks like with some good soldering skills the relays could be replaced if needed.

Originally Posted by Dominick

A breakdown of relays in the CCRM

[Poppy]

any updates?

[joshtimber]

Is there any way to check AC system digitally? I mean to say to check it with any device which tells exactly where the fault it?