Can I by pass the fan relay by using the red wire from the relay harness to a on off switch and connect the other wire to the fan ?

I have replaced the relay. The fan will not work with or without the A/C on. I can take a jumper wire from the fan to the battery and the fan comes on full blast.So I guess the fan is ok.

Or is there someone located in Houston that can fix my problem. Corvettes of Houston could not.

Also where do you fill out my profile on this website.

 

To test the ECM and relay, you can jump the "A" and "B" terminals of your ALDL with the key "On" engine "Off". That should run the fan. For the ECM to run the fan from the A/C, the pressure switch has to be activated. When the ECM senses the A/C it will run the fan. You can check the switch and the associated wiring if the ALDL test is positive.

The switch you propose switches the full fan current. Not a great idea.

RACE ON!!!

 

That's the purpose of a relay, to switch a large current using a much smaller one.

If the ECM fan control test above fails, test the relay by jumpering the Dk Grn/Wht wire (at the main fan relay) to ground with the key in Run and the main fan should come on.

 

Test all the inputs to your relay. The relay is triggered by the ECM supplying it with a ground path. If you ever plan on putting in a fan switch, use the switch to supply the ground to relay, much safer.
Read this and test away
http://members.shaw.ca/corvette86/Co...%20Control.pdf

 

The main fan should come on with the coolant temp at 226 degrees or pressure on the a/c high side at 220 psi (about 150 degrees at the Condensor). I don't understand how a shop couldn't diagnose this as a scanner would show what the Coolant Temp Signal is and as you're looking at that, it's easy enough to look at the fan. You do need a Manifold Gage Set to see refrigerant pressure, but most full service shops have one of those too. Since the a/c switch simply opens the circuit signal from the ECM when it reaches 220 psi, it's easy enough to make the ECM "think" the pressure is that high by disconnecting the switch and doing so should turn on the fan. The switch is mounted on the high pressure or smaller line from the Condensor to the Evaporator. It's next to the high pressure switch (a fail safe device that cuts power to the compressor clutch if the high side gets plugged up). Whichever one turns on the fan disconnected is the switch you want. If the fan isn't coming on with a/c requested, the pressure hasn't reached 220 psi and if it's below 50 degrees, that's a possibility. It could also be that the a/c is out of refrigerant and if the compressor isn't engaging, that's a good sign that it's all leaked out. If the compressor is engaging and the air out the vents gets warm at stoplights, the switch might be bad. They're about 9 Bucks or so at a Dealer. Just make sure the fan comes on first by disconnecting it. If it doesn't, the wire is shorted to ground somewhere or the ECM is bad.

Out of curiosity, what exactly did Corvettes of Houston tell you or write on the work order - "No Problem Found" maybe? How did you drive your Vette to and from the Shop without it overheating?

Grounding the diagnostic switch is a quick and easy test to see if the ECM is capable of grounding the fan. It's far better to let the ECM work as designed (particularly for a/c) which is to provide a ground for the Relay. That's the DarkGreen/White wire at the Relay. It's switch side is powered up by Pink which is from the ECM fuse (and if your Vette is running, you know that fuse is good) - ground the DarkGreen/White and that turns it on, allowing power from a fusible link (red - from behind the battery) to flow through it to Black/Red which turns on the fan. To bypass the ECM, you monkey with the ground side - can't recommend it - but it's your Vette.

 

I guess I should have told you this. There are 2 wires from the fan. 1 of them is the black wire with a red stripe. If I connect that wire to the fan the car will not start. so I have it dissconnected.

The weather has not been hot yet. So as long as I am driving on the freeway it runs at 185 with the water wetter and 25 % coolant.

But if I get into traffic it gets hot fast.

i just bought the car and the fan used to come on when the a/c was on but now its does not. The A/C is working but I think its needs some freon. The compressure does not stay on long and blows warm air. I had the car up to 245 in the garage and the fan has never come on by its self. I am asuming that because the black wire is not hooked up.

I think I must have a short somewhere if when I connect the black wire with a red stripe the car will not start and I blow a fuse.

My Shelby sure is easier to work on. But I love the vette. If I could just fix this problem I would be happy.

Thanks in advance for all your help!!!!!!!!

 

For starters you should get yourself a FSM. The red/black wire is 12 volts that is switched by the relay. With a new relay, it is hard to figure how connecting it prevents the engine from starting. What fuse to you blow? The red/black wire is connected directly to the battery via a fusible link. It shouldn't be connected to a fuse. Did I mention that you need a FSM?

RACE ON!!!

 

Ok fan motor has two wires:
Blk - goes to ground
Blk/Red - goes to the coolant fan relay pin A. This is the wire that supplies power to the fan when the relay is activated.
When the relay is activated power comes through a fusable link through the Red wire to pin B of the relay.

With the ignition on and the relay plugged in does the fan come on if you ground the relay pin with the Dk Grn/Wht wire??

What fuse is blowing? Is it the C.Fan Fuse? If so that is preventing power from going to the starter circuit. If this fuse is blowing there is a short in Dk Blu wire between that fuse and pin D of the relay.

What do you mean the engine won't start?

If an electrical diagram of that wiring will help I can take a pic of that page in my '88 FSM and email to you.

 

Ok I am not able to ground the rely pin that has the green wire since the blach/red wire is not connected. The engine turns over but will not run with the B/R wire connected.

The fuse that blows is the Fan/ecm

If you can please call me 281-389-3590 thats my cell or 281-955-9356 and call me collect. Maybe we can fix this over the phone.

 

This is an '89 so there isn't any fuse per se - relay switch power is via the ECM fuse on a pink/black wire - black at the Relay - if that opened, it isn't going to run regardless of what the fan does. What did the shop say? Sometimes that helps.

 

WOW Thanks to 65Z01 for all your help!!!!!!!!! He fixed the problem.

Call me when you ever come to Houston and I will by you a beer.

Thanks again for your help and every one that gave suggestions.

 

I was thinking that the 89 is wired like my 86 with the fan having it's own fuse. I keep linking people to my 86 schematic and would like to know if there is a difference between 86 and 89 fan schematics.
Thanks

 

Glad to be of some help, thanks for the offer...

Yes there is a difference. My '88 is like this:
-ECM coolant temp sensor - in the front of the intake base
-gauge coolant temp sensor - in the block below #6 & #8 spark plugs
-aux fan sw - in the block below #1 & #3 spark plugs

The ECM only controls the main fan behind the radiator; the aux temp sw only controls the booster fan in front of the radiator.

I believe this is also the setup starting in '87 and running through '89. I think that '90 & '91, with the dual fans, used a little different setup.

 

That part is the same 86-89. It's the fan fuse in this thread that has me wondering. My 86 has it's own fan fuse, but in ths thread I'm seeing the 89 fan sharing the fuse with the ECM.

 

Actually the fuse being blown here was the ECM/IGN Fuse, not the C.Fan Fuse (according to my '88 FSM). Though he said that fuse was labeled ECM/FAN Fuse in his '89 Owner's Manual.
Now I wonder if maybe there is a difference in wiring between the '88 and the '89 but don't have an '89 FSM for reference.

I am still puzzled why that was happening because (by my '88 FSM) there is no direct connection between those two fuses.

I could only think that there was some issue within the new fan relay so had him install the old relay and then test fan op by grounding the Grn/Wht wire.

After that the fan "magically" worked without blowing a fuse, though we still do not know what was the problem prior to swapping the relays.

BTW, I had him open the connector to the pressure sw in the A/C line so that the ECM would bring on the fan soon as the engine was started.

 

Looking at SunCr's post, he mentions ECM/Fan fuse also. It seems the 89 is wired a bit different in regards to the fuse.

 

'89 has some changes and to see all of them, you'll need the electrical supplement and the foldout schematics at the end of the Manual (where it shows that the wire to nowhere at my fuel pump was intended for the ZR1). Relay is no big deal. One wire is going to be from fused ignition power, another ECM for the ground or to turn on the Relay. Other wires will be fused battery (links through at least '90 - I think) and then main to whatever device is being powered up. I know at some point (at least by '95) GM dropped the Links and simply went with high amp fuses usually clustered in a box under the hood.