C4 Fan Control
Thread Starter
6th Gear
Joined: Jul 2021
Posts: 6
Likes: 0
C4 Fan Control
Hey guys,
I just did some cooling upgrades on my 93 Vette including a Dewitt Radiator, new water pump, thermostat, and temp sensor. I also removed the A/C and put a dummy pulley in its place.
I cranked the car yesterday, and neither fan will come on now. The fans were working fine before the upgrades, and I reconnected everything as it was prior. The thermostat seems to be working fine, and I put power and ground to the fans confirming they still work. It looks like one of the fans is tied to the A/C, which could be part of my issue.
Any ideas on how I can trouble shoot this? I'm not really sure on what to check.
Thanks in advance!
I just did some cooling upgrades on my 93 Vette including a Dewitt Radiator, new water pump, thermostat, and temp sensor. I also removed the A/C and put a dummy pulley in its place.
I cranked the car yesterday, and neither fan will come on now. The fans were working fine before the upgrades, and I reconnected everything as it was prior. The thermostat seems to be working fine, and I put power and ground to the fans confirming they still work. It looks like one of the fans is tied to the A/C, which could be part of my issue.
Any ideas on how I can trouble shoot this? I'm not really sure on what to check.
Thanks in advance!
Drifting
Joined: Jan 2021
Posts: 1,312
Likes: 383
From: Northern California
Congrats on the upgrades. The Dewitts are great. Everyone here with experience will tell you to get a Factory Service Manual (FSM). They're not wrong. It will help you trace the circuits, controls, sensors, and logic.
Tell us more about the temp sensor. You mean the coolant temp sensor for the PCM? or the gauges? The secondary fan is affected by the A/C system but the primary should be controlled by the PCM and the signal it sees from the coolant temp sensor.
Tell us more about the temp sensor. You mean the coolant temp sensor for the PCM? or the gauges? The secondary fan is affected by the A/C system but the primary should be controlled by the PCM and the signal it sees from the coolant temp sensor.
Thread Starter
6th Gear
Joined: Jul 2021
Posts: 6
Likes: 0
Thank you! I'm looking forward to seeing how to car drives with the improvements. The sensor I am referring to is the one in the water pump. I know this isn't the best practice, but I noticed momentarily unplugging the 2 wire pigtail from the sensor in the driveway made the fans come on. When I plug it back up, the fans continue to run for 30 seconds to about a minute, and then cut off again. I tried flip flopping plugs on the fan relays to eliminate this as a potential issue, but this didn't seem to do anything.
I must be honest, I kind of just took all of the A/C equipment out, leaving the harnesses that were previously plugged into the A/C zip-tied off not hooked to anything. I am also getting a H66 code on my ECU.
Does any of that help explain how to fix these fans to come on properly?
I must be honest, I kind of just took all of the A/C equipment out, leaving the harnesses that were previously plugged into the A/C zip-tied off not hooked to anything. I am also getting a H66 code on my ECU.
Does any of that help explain how to fix these fans to come on properly?
Racer
Joined: Jun 2019
Posts: 390
Likes: 126
From: Franklin, TN
on a 93 vette the primary fan (drivers side) will come on when the coolant temp is 227F (manual says when it exceeds 226F). This fan will operate until the coolant temp drops 9 degrees. The secondary fan will come on when the coolant temp reaches 235F and will operate until the temp drops 9 degrees. Note this connection to the A/C that you removed. The secondary fan will also come on anytime you turn on the A/C. There are other conditions, such as oil temp, that will turn on the fans.
Last edited by jrobin1; Aug 30, 2021 at 09:39 PM.
Thread Starter
6th Gear
Joined: Jul 2021
Posts: 6
Likes: 0
Okay, thanks for the info. Seeing as I have disconnected all of A/C plugs, and have a dummy pulley in its place, is there anything I need to do to make the fans come on properly?
Or should I be in good shape for he fans to come on as I have things now?
I'm just trying to make sure both fans will work and come on like they should since I pulled to A/C. I've been apprehensive to drive the car because I want to make sure there isn't something I need to do with the wiring before venturing far from home.
Thanks!!
Or should I be in good shape for he fans to come on as I have things now?
I'm just trying to make sure both fans will work and come on like they should since I pulled to A/C. I've been apprehensive to drive the car because I want to make sure there isn't something I need to do with the wiring before venturing far from home.
Thanks!!
Racer
Joined: Jun 2019
Posts: 390
Likes: 126
From: Franklin, TN
I am running an overheating issue which is why I had that info at my finger tips. I let mine idle in the drive way until it reached operating temperature and observed the fans operation and while checking the digital temp gauge. You can also see if the fan comes on when you turn on the A/C by just turning it on and observing. I was suggesting that since the secondary fan is tied in to the operation of the A/C, removing the A/C may have adversely affected the entire circuit for fan operation. I am not familiar enough with the circuit to give a solution.
Race Director
Joined: Jan 2012
Posts: 17,062
Likes: 166
From: United States
If you disconnected all the AC plugs, plug them back, turn ac controls on and see if fans work?
Also you can jumper the ALDL connection, A and B I believe, and the fans with ignition on will turn on.
Also you can jumper the ALDL connection, A and B I believe, and the fans with ignition on will turn on.
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