You all are going to see a lot of posts from me over the next few months. Just purchased a 1986 Fiero GT with 2.8L. The guy I purchased the car from had issues with radiator fan to turn on or overheating. The radiator fan has been hotwired to run constantly. I would like to return the operation of the fan to factory spec. When I look at the fuse box (interior) there is a green wire that runs from the front of the car to a green fuse in the box. I’ve never seen a wire run external to a fuse box. Would it be hotwired from the fan direct to fuse box? How would a mechanic typically wire a radiator fan to run constantly? Trying to figure out someone else’s rigging is not fun.
If the fan was not turning on, is the issue likely a faulty temp sensor for the fan. Little more history, the car has the original AC setup and is low on R12, no cold air. Could that trigger the fan not to operate? I know the fan is set up to turn on when AC is turned on. Didn’t know if that could play into the issue. As always, thanks!
The fannis controlled by the FAN switch on the engine (or the HVAC control on any A/C setting) providing a ground to the FAN relay, located on the front bulkhead ahead of the driver side headlight.
The easiest way to trigger the FAN would be to provide a ground to the relay coil.
MasterBaker The radiator fan has been hotwired to run constantly.
Fact or Theory?
A/C equipped vehicles have a separate signal wiring to the ECM for a fan control [edit: for L4 engines When the A/C control switch is on, the ECM gets the A/C "On" voltage on pin 21 and closes the ECM coolant fan relay control to ground. The A/C clutch does not have to be engaged for the ECM to turn the ON the fan.]
Edit: On V6, the A/C Pressure Switch closes to run the radiator fan.
IF an A/C Pressure Switch Fails (Grounded) then the radiator fan can be "On" constantly.
Without Any 'History' on the Car: My suggestion is to disconnect the A/C Pressure Switches from the A/C Compressor, then run the engine....
If the radiator fan stops, then maybe you found the source.
Edit: Ask me why I know....
[This message has been edited by Vintage-Nut (edited 08-23-2023).]
Just to possibly elaborate on the points you brought up... I removed all A/C components from my Formula (I used the car for autocross and didn't want the added weight of something I didn't use), but I retained the A/C dash controls. I still have full manual control of the rad fan using the A/C controls, and the fan switch (Dickman 210° on and 200° off) works normally as well.
[This message has been edited by Patrick (edited 08-22-2023).]
IF the A/C control is 'Off' AND the A/C Pressure Switches from the A/C Compressor are disconnected, AND the radiator fan stops; then maybe MasterBaker found the source.
IF not, then I believe the fan has been 'hotwired' to run constantly....
A/C equipped vehicles have a separate signal wiring to the ECM for a fan control.
Not. Most Fiero ECMs don't care or know about fans.
ECM have 2 pins for AC 1. Input. All switches closed telling ECM you turn On AC & limit switches are happy. 2. Output. Final Say that AC Clutch to turn On. Because ECM will Not turn the AC under rules in it's programing. Like Will Turn Off AC when you "floor the gas pedal."
Some cars have AC Limit Switches wired to Rad Fan control. All 87-88 Fiero Duke ECM control the rad fan all the time not just for AC, Even has support for 2 speed rad fan but unused ECM pin for Fiero & most others.
Either way Fiero AC/heat head bypass that when AC is On and force On the Rad Fad and V6 blower (for cars w/ them). So make sure head has Off Button is Push Down. (That's the only way to Turn Off the Heater Blower too.)
If fan is still On... 1. is pull E-fan Fuse to see if control wire & fan relay actually work and fan(s) turns off. If true... then need to find out where green wire is grounded. If false... Fan relay can be bad or Fan is wired to bypass the relay. But note that Bad Relay often want to stay On even w/ I-key is Off because Big Main power wire runs directly to the battery via Fusible Link A
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
Thank you all so much! I follow everyone’s suggestions. Fan turns on as soon as ignition switch is turned one notch forward. Next I took an closer look at radiator fan wires. I noticed a black wire running out of snakeskin with a wire splice. Some mechanic cut the black red wire and ran a black wire thru the front wall at steering wheel straight to outside the fuse box. He used a metal clip and wired it where the fuse plugs into the fuse box. 😡 Not impressed at all. The former owner told me car didn’t not overheat but was worried fan did run much and temp were up over 200 degrees. He told the mechanic the sensor may be bad. Mechanic totally rigged it.
Question on the AC switch that turns on radiator fan. If the system is low on Freon will that disable the switch when you turn on AC inside car. Car does not blow cold air at all. It’s very low on Freon. Didn’t know if that switch also relies on gas pressure inside AC system to trigger fan.
Patrick my bad. I apologize! I did over look you post last nite. Thank you so much for helping my understand how the cooling system functions with fan operation. Can’t thank everyone enough for your input!
Originally posted by MasterBaker: The former owner told me car didn’t not overheat but was worried fan did run much and temp were up over 200 degrees. He told the mechanic the sensor may be bad. Mechanic totally rigged it.
Question on the AC switch that turns on radiator fan. If the system is low on Freon will that disable the switch when you turn on AC inside car. Car does not blow cold air at all. It’s very low on Freon. Didn’t know if that switch also relies on gas pressure inside AC system to trigger fan.
1st problem is Engine is Not "Running Hot" running @ 200-230°F = The PO had no clue and "mechanic" is ripoff shop.
AC Limit switches Will Not disable the Rad Fan. Low switch can stay on w/ low pressure so compressor does little but when any are "off" then ECM says No AC and won't run the AC Clutch.
As you can see, the fan temp switch closes at 235F, opens at 225F. So technically not over heating as it's designed that way, but starts getting close to the "red" on the gauge. At my altitude (3500 ft) the engine sure didn't like it before the fan kicked in.
[QUOTE]Originally posted by MasterBaker: The former owner told me car didn’t not overheat but was worried fan did run much and temp were up over 200 degrees. He told the mechanic the sensor may be bad. Mechanic totally rigged it.
Question on the AC switch that turns on radiator fan. If the system is low on Freon will that disable the switch when you turn on AC inside car. Car does not blow cold air at all. It’s very low on Freon. Didn’t know if that switch also relies on gas pressure inside AC system to trigger fan.
1st problem is Engine is Not "Running Hot" running @ 200-230°F = The PO had no clue and "mechanic" is ripoff shop.
AC Limit switches Will Not disable the Rad Fan. Low switch can stay on w/ low pressure so compressor does little but when any are "off" then ECM says No AC and won't run the AC Clutch.[/QUOTE]
I spoke with the former owner of the car. He is beyond pissed the mechanic hotwired the fan and didn't address his concerns. Especially when he didn't necessary have an overheating issue. Car came from PA. Fan likely wouldn't of kicked on much up there. Plus he lived in the country side, no stop and go, all highway miles. Think he saw some higher temps on the gage and told the mechanic to change temp sensor or radiator temp fan sensor. The mechanic just rigged the damn thing for pennies on the dollar. He never addressed any of the issues or concerns. I am working on getting it reworked back to factory. I am going to replace both sensors to make sure temp is accurate and to make sure fan kicks on at the correct temp too.
In 2003, I heard that my '88 GT Radiator Fan was "On" on a cold start with the A/C control "Off".
As the factory A/C stopped working (no cold air) and the compressor belt was removed years ago; I found that the A/C High Pressure Switch had shorted to ground causing the fan to run constantly.
By disconnect the A/C High Pressure Switch from the Compressor, the problem was solved, and the fan switch and the fan have been working properly after the event.
[This message has been edited by Vintage-Nut (edited 08-23-2023).]
Similar situation on my bucket list to repair: A month ago, I brought an 87 Fiero 2.5 with an overheating issue right after start, requiring the ac switch to be on in order to run the fan to avoid overheating. I showed theogre back then a photo of a cluster wire with 3 plugs sitting unconnected in the engine bay and he identified them connectors to the ac compressor. The funny thing is that this Fiero did not have a compressor at all connected to the engine, just a spool of some sort in its place running with the timing belt.
I don’t want to interrupt MasterBaker’s post, but I mentioned this if it by chance relates altogether with overheating. Thanks MasterBaker for this important topic and to everyone involved.
[This message has been edited by Fieros4evr (edited 08-23-2023).]
In 2003, I heard that my '88 GT Radiator Fan was "On" on a cold start with the A/C control "Off".
As the factory A/C stopped working (no cold air) and the compressor belt was removed years ago; I found that the A/C High Pressure Switch had shorted to ground causing the fan to run constantly.
By disconnect the A/C High Pressure Switch from the Compressor, the problem was solved, and the fan switch and the fan have been working properly after the event.
Going to splice the radiator fan wire back to factory this weekend. I am very interested to see if the A/C high pressure switch is functioning with low pressure/Freon in system. Thanks to the forum members I will be able to trouble shot the current issue and now know that the A/C pressure switch can defaulted to ground. I would have never thought about looking at that switch had it not been for the members commenting in the thread. No I know it can be unplugged to allow the fan to operate from the fan temp sensor. Great stuff! Thanks all.
[This message has been edited by MasterBaker (edited 08-23-2023).]
If splicing wires up front etc... Use "Weather Proof" crimps preferred 3M ones and good crimper. Crap crimpers often cut the heat shrink tube trying to crush the metal part. Then shrink the tube to melt the "glue" to seal it.
Clean the wire(s) plastic before crimping so "glue" works better.
[This message has been edited by theogre (edited 08-23-2023).]
