1985 Coolent Sensor Woes
Thread Starter
Burning Brakes
Joined: Oct 2002
Posts: 971
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From: Rockwood TN
1985 Coolent Sensor Woes
I've did a thorugh search through the archives and followed some of the suggestions but I've still got the same problems.
After reading through the post here's the configuration on my car.
1. Auxilary Fan Switch is located between #6 & 8 spark plugs.
2. Gauge Switch is located between #1 & 3 spark plugs.
3. ECM Switch for the main fan is located under the thermostat housing.
OK here's my problem The aux fan will not come on when the AC is turned on and my temp gauge always reads Lo.
Here's what I've done so far. I replaced all 3 switches. I read in a post that you could ground the connector for the aux fan and it should come on so I did this and it came on so the fan is good. Also I read something on a post about a high pressure switch on the AC line but I can't find the post again
Thanks Bill
After reading through the post here's the configuration on my car.
1. Auxilary Fan Switch is located between #6 & 8 spark plugs.
2. Gauge Switch is located between #1 & 3 spark plugs.
3. ECM Switch for the main fan is located under the thermostat housing.
OK here's my problem The aux fan will not come on when the AC is turned on and my temp gauge always reads Lo.
Here's what I've done so far. I replaced all 3 switches. I read in a post that you could ground the connector for the aux fan and it should come on so I did this and it came on so the fan is good. Also I read something on a post about a high pressure switch on the AC line but I can't find the post again
Thanks Bill
Le Mans Master
Joined: Sep 2006
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From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
my fan switch is between #3 and #1, and the temp gauge is between #6 and #8.
Are you sure nobody did a valve job on your heads and didn't switch sensors on yours?
Are you sure nobody did a valve job on your heads and didn't switch sensors on yours?
Thread Starter
Burning Brakes
Joined: Oct 2002
Posts: 971
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From: Rockwood TN
Yes I grounded the connector between 6&8 and the aux fan came on. I think in 86 the General changed things to the opposite side. On the driver side on mine is a spade connector.
Thanks Bill
Thanks Bill
Last edited by Bullyj; Jun 23, 2009 at 09:20 PM.
Team Owner
Joined: Jan 2003
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From: Summerland B.C. Canada
I recall something about the 85's aux fan being wired a little different(other than the fact they have sender/switch in opposite heads), but I don't recall the aux fan being used in AC operation, just like 86-89.
Your gauge problem could be an open circuit.
Your gauge problem could be an open circuit.
Thread Starter
Burning Brakes
Joined: Oct 2002
Posts: 971
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From: Rockwood TN
Thanks Agent 86 I will try this later on today while the boy is at day camp. As for the aux fan I just assumed it would come on when the AC is on to put more air flow across the condenser.
Race Director
Joined: Sep 2000
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From: The Top of Utah
Bullyj,
The devices in the left head and intake manifold aren't switches, but sensors or sending units. Check your FSM or owners manual to be sure which, if either, fan is supposed to come on with the A/C. Your main fan is controlled by the ECM. It comes on when the programming tells it to. If the A/C signal goes to the ECM, more than likely it is the main fan that operated with the A/C. The auxiliary fan has no connection to the ECM. The aux fan switch grounds the primary side of the aux fan relay to run the fan. If the A/C switch also grounds that circuit, that will activate the aux fan. The unique fan wiring in the 1985 is in cars that don't have an aux fan. Before you can fix it, you have to know how it is supposed to work. Check your literature, but it is my guess that it is the main fan that is influenced buy the A/C operation.
RACE ON!!!
Last edited by CFI-EFI; Jun 24, 2009 at 11:11 AM.
Race Director
Joined: Sep 2000
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From: The Top of Utah
As for your temp gauge, you may have an open circuit, a broken wire between the sensor and the readout, or possibly a bad sensor. With the wire disconnected from the sensor the readout should say "Low". With the wire grounded is should read the highest reading possible, 299°, 300° or whatever is max. If the readout responds correctly, the gauge and wiring are good. Make sure you have a good connection with the sender, and if so you need a new temp sending unit.
RACE ON!!!
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Thread Starter
Burning Brakes
Joined: Oct 2002
Posts: 971
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From: Rockwood TN
I grounded the aux fan yesterday and it came on as it should. Also I replaced the gauge sending unit yesterday. I grounded the connector for the gauge sending unit and it still reads low. I guess my next step should be to trace the wire and check for breaks. Where does this wire feed back into the harness. I see it going in between the block and the exhaust manifold but I can't see or feel it below there.
Thanks,
Bill
Thanks,
Bill
Race Director
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From: The Top of Utah
My 1984 FSM shows the temp gauge sender wire to be blue. At C342 it connects with a dark green wire. The dark green wire goes through the bulk head connector on pin C2 and then on to the cluster where it connects on cluster pin #D4, "Coolant Temp Sensor Input". I don't know how much of that applies to your 1985. My guess would be, all of it.
Melting Slicks
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From: AZ
Thread Starter
Burning Brakes
Joined: Oct 2002
Posts: 971
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From: Rockwood TN
I traced the gauge sensor wire in the engine compartment and found one bad place. I repaired it but gauge still reads Lo. The tach part of the gauge cluster has issues so I believe my problems with the coolent temp must also be in the gauge cluster. I plan on having the cluster rebuilt so I'm going to wait till I have this done before moving ahead on the temp gauge.
Thanks for everyones help
Bill
Thanks for everyones help
Bill
Race Director
Joined: Sep 2000
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From: The Top of Utah
Great help,!
I have never heard if an '85 that didn't have the main fan run by the ECM. The 1985 with no auxiliary fan was set up like no other C4, but as far as I know, all 1985s had the computer controlled main fan. Do you have any documentation? If that is the case, I'd like to know.
RACE ON!!!
RACE ON!!!
Race Director
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From: The Top of Utah
Le Mans Master
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From: San Diego, Ca
Before you send the Cluster out, jumper Pin D4 to ground and see what happens. If that gives it max (something around 300), check the wire again. It passes through Big Connector behind the battery at C2 - should be green on the '85. '84 was blue at the sender, then green behind the Big Connector to the Cluster.
ECM controls the Main Fan based on Coolant Temp Senor input or a Pressure Sensor mounted on the A/C High Pressure Line. That sensor opens at around 230 psi which causes the reference voltage to rise at the ECM. When that happens, the ECM drives the Fan Relay. Disconnecting the Sensor wire simulates the open and should turn on the Fan.
Aux fan isn't used for a/c. Service Bulletin described it as a Dealer installed accessory following overheating complaints from High Altitude Users and Autocrossers. Later a Factory Option. Really shouldn't come on at all.
ECM controls the Main Fan based on Coolant Temp Senor input or a Pressure Sensor mounted on the A/C High Pressure Line. That sensor opens at around 230 psi which causes the reference voltage to rise at the ECM. When that happens, the ECM drives the Fan Relay. Disconnecting the Sensor wire simulates the open and should turn on the Fan.
Aux fan isn't used for a/c. Service Bulletin described it as a Dealer installed accessory following overheating complaints from High Altitude Users and Autocrossers. Later a Factory Option. Really shouldn't come on at all.
Race Director
Joined: Sep 2000
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From: The Top of Utah
Before you send the Cluster out, jumper Pin D4 to ground and see what happens. If that gives it max (something around 300), check the wire again. It passes through Big Connector behind the battery at C2 - should be green on the '85. '84 was blue at the sender, then green behind the Big Connector to the Cluster.
RACE ON!!!
