Blu

I have had this problem for a while but sort of band aid fixed it for a while and just didn't run the AC when driving the car.

For some reason my 99 Corvette tries to over heat when running the AC but I believe the #49 fuse was already blown at the time of the problem. For some reason it will idle for a while but it blows the 30 amp 49 fuse so I have a problem somewhere else it seems. Now a 30 amp fuse wont last too long so we tried a 40 amp fuse. I doubt this is safe but it works for about 2-3 weeks before it blows the 40 amp fuse. What could be causing this issue?

Now onto the car over heating, its fine and doesn't run abnorally hot with the AC off even in stop and go its about whats considered normal. Once I turn the AC on the temps immediately start rising. Could this be a short in the wiring or possibly my fans are kicking the bucket? Im not mechanic nor do I attempt to be, Im just looking for options to give my mechanic to start with. I am going to replace the fuse today with a new 30 amp and run the AC and see how the car reacts.

Im thinking about ordering new fans and a Dewitts and replacing it all for added protection and hopefully solve it.

Any ideas or tech help?

Blu

Forgot to add when it blows the fuse it shuts the car off, goes into reduced engine power. I shut the car off andclear the codes and fire it right back up. It didn't even throw the low fan circuit codes this time but the fuse is blown.

bestvettever

Hi, need a little more info. What fuse # is blowing. FYI the 3 fuses for the fan operation are #49, 46, 14. Fuses 49, and 46 are 30a, and 14 mini fuse is 10a. All are in the underhood fuse block. They power relay 45 for low speed, and relays 43, and 44 for high speed. the signal to run the fans is sent by the pcm by grounding the circuit. Turning on the AC powers the high speed fans to run. Both fans should always run together when called to run, at either low or high speed. Does the fuse blow at any other time such as when the high speed fans is called to run by temps over 235f, and the AC is not on? As a rule of thumb you should probably check the radiator and condenser for blockage by dirt or debris, in between the two, and the fans openings for debris. Excessive heat there may cause the fans to run hot and blow a fuse. if the fuse blows whenever the high speed is called for the relays 43, and or 44 may be shorted.
Good Luck
SEE EXPLANATION BELOW
Good Luck
++++++++++++++++++++++++++++++++++
Cooling Fan Control
The engine cooling fan system consists of two electrical cooling fans and three fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage and ignition 1 voltage from the underhood electrical center. The ground path is provided at G102.

During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the cooling fan 1 relay coil, closes the relay contacts, and supplies battery positive voltage through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the cooling fan 3 relay and the right cooling fan. The result is a series circuit with both fans running at low speed.

During high speed operation the PCM supplies the ground path for the cooling fan 1 relay through the low speed cooling fan relay control circuit. After a 3-second delay, the PCM supplies a ground path for the cooling fan 2 relay and the cooling fan 3 relay through the high speed cooling fan relay control circuit. This energizes the cooling fan 3 relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the cooling fan 2 relay coil is energized closing the relay contacts and provides battery positive voltage on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.

The low speed cooling fan is commanded on when the coolant temperature reaches 108°C (226°F). It is turned off if the coolant temperature lowers to 104°C (219°F). The high speed cooling fan is commanded on when the coolant temperature reaches 113°C (235°F). It is turned off if the coolant temperature lowers to 108°C (226°F). When the A/C is on and the coolant temperature reaches 85°C (185°F), the low speed cooling fan will be turned on at vehicle speeds less than 56 kPh (35 mph).

Blu

Fuse 49 is the one that blows and it blows when the AC is not running.

lucky131969

First of all, you NEVER install a larger fuse when a fuse blows..keep uping the fuse value, and eventually something will fry.

when you turn the a/c on, the pcm commands the fans to low speed mode. As a result, mini relay #45 is energized, and power is supplied through the relay contacts (powered by Maxifuse #49) to both fans. So if you blow fuse #49, you could have a faulty mini relay #45, or one of the fans shorting to ground or just drawing too much current. Also, any of the wiring in between the relay and fans could be suspect.

Finally, I confused by your posts. In your first post, you state: " For some reason my 99 Corvette tries to over heat when running the AC and will immediately blow the low fan circuit 20 amp fuse"

Then later, you state: "Fuse 49 is the one that blows and it blows when the AC is not running"

First of all, fuse 49 is a 30 amp, not a 20 amp......so I'm not sure why a 20 amp fuse would have been in that location.

Second, does it blow the fuse with the A/C on or not? First post you say it does, then later you say it doesn't.

It really helps to be clear when requesting help.

Blu

Sorry for the confusing first post. My fuse blows without the AC running. I am going to buy a new 30 amp fuse and see where I can get a new mini relay and replace that and see what it does. I just haven't ran the AC in a while and the last time I tried to run it Im pretty sure the 49 fuse was already blown. I am going to head to Autozone and see if I can get the mini relay and replace the fuse as well with a 30 amp and see what happens. Im not very technical so sorry for the confusion and I will edit my first post.

lucky131969

Ok. At least you'll have the relay out of the equation, although, it's probably going to be one of the fans or wiring. Keep us posted.

Blu

If that doesn't help I will probably just get new fans and the Dewitts radiator and knock it all out at once. I had planned to upgrade before next summer here but I guess it worth it now to get it all out of the way if the problem continues.

lucky131969

Well, I've heard that the Dewitts radiator and fans are a solid upgrade, but if don't trouble shoot the problem, and just replace the fans, you might miss a wiring problem, and be back to square one anyway......and your wallet will be light about $600.....still blowing the fuse.

Blu

I will make sure that all the wiring is given a one over during the install. Upgrading and hopefully eliminating one headache at the time.

dgrant3830

I will suggest one other possibility although its not high up on the list.. the ground pack located at the forward right frame rail adjacent to the hood riser. The fan grounds go through it. If the grounds opened up, I would expect that they wouldn't run but if its getting a ground through some other path, then it could overload whatever associate fuse. It could be that your fans are dragging with worn out bearings, therefore drawing too much current. There are two relays in the engine compartment fuse bos for the fans. You can take the covers off, plug them back in and manually close the contacts. This will cause the fans to come on at low speed, then manually doing the other one, will cause the high speed fan function by it changing ground paths... simply put, then run low speed by running them in series. When on high speen, each fan is grounded seperately. You do not have to turn on the car to do this. They are hot all the time.

lucky131969

Please explain....

dgrant3830

The ground pack at the right forward frame rail is where the fan ground connections run through. If you disconnect the ground pack from the frame, the fans will supposedly stop running, fog lights, I think the headlamps too and other front end items. Mine ground lug on the frame for this ground pack, '99 Coupe, was loose. The engine started overheating unless I was moving through the air or down the road as such. When I got home, I found the ground pack was loose and touching it, a slight spark between it and the rail. The nut was loose. When I went to tighten it, it fell off the frame completely. I hardwired a ground to the frame for the ground pack to compensate.

Blu

any chance you can post a picture of what you are talking about, that is unless you want to drive to Charlotte and show me

dgrant3830

Sorry, I can't. I gave away the car to my son in May and its 3,000 miles away from me now. I also gave him the manuals. Just look at the forward right frame rail next to the hood riser. You will see a black plastic thing with wires going in on one side and a grounded tab on the other.

lucky131969

I guess I was trying to understand your post. How would the fans getting a ground from another source overload fuse? Unless it's power to ground (obviously undesirable), what's the difference?

dgrant3830

In electrical circuits, a path to ground is what the current is going to look for. With ground packs, therefore multiple items looking for the same ground path, if the normal one isn't there, it may try to get a ground through another path such as a lamp path providing its turned on. Lets say something else on that path, has a ground path through it due to design, if the normal path isn't present, the fans may go through something else to ground. My carpooler, his car had a problem with the headlamps. The ground path opened up, so it back-tracked itself through a lighting control module which burned up in a small cloud of smoke. He got another one, and lost it too before he realized the cause was a bad ground.
I suggest you do as I suggested earlier. Take the top off the two fan relays in the engine compartment fuse box and plug them back in. One of them will turn on the fans to low speed, both as the ground for the first one, passes in series through the second fan and finally to ground. You can turn it on by simply pushing the relay armature. They are powered all the time so you don't need the key turned on. Check at that time for the fuse to blow or use a "current meter" to measure the amount of current being drawn. Then push the other relay and the fans that were running in series will now both seperately be grounded therefore they will both come on to high speed. Again, measure the amount of current being drawn. Either current draw should not exceed the size of the normal fuse. If it is, then a fan or both are having problems. Again, make sure the ground pack is properly grounded to the frame.

lucky131969

Thanks.....I thought other's might want a little more in depth explanation.

Blu

Well not much of an update but I installed a new 30 amp fuse. Decided to try to run the a/c on the way home to see how the car would react. Well temps started to rise when I turned the a/c on so I turned it off and wala they started falling. I get home and check the fuse and it is blown.
I couldn't get the replay because it had to be ordered but I have a feeling its something a little more in depth. This just blows!

jimcork1

Perhaps you can help. I have a problem with both fans not running. The relays / fuses have been checked and are good. The relays were grounded out and the fans do run. I am concerned it is the control module. Any thoughts.? Jim