2007 cat 700 efi fan issues

[kraft]

I have fan issues , fan will not come on when powered up from factory plug. The fan will run when powered directly from battery or when + side of feed plug is used and fan is grounded to frame separately. Replaced fan temp sensor with Caltric one. Also when powered from battery into the temp sensor plug the fan will start when warmed up, but will not shut of till power is off from battery feed. Then fan stays off till temp reaches 90 and will start again. New battery also. Any thoughts out there? Checked voltage across factory feed plug, lower voltage than from + feed on plug to chassis ground. Diode issues?

[Mech]

Diodes usually drop voltage about 0.4-0.5 of a volt..

Are you sure the fact the fan stays on once it's started, isn't because the motor is getting too hot ? And the fan isn't cooling it enough ?

[kraft]

No, temp is good. To sensor out and it stays closed.

[Mech]

I'd test the temp sensor in a pot of water, with some load on it, like a headlight bulb..  Perhaps it... err... sticks ?

[mikeexplorer]

Agreed, fan sensor is probably sticking. I had that issue once.

 

[kraft]

Took temp sensor out, permanently stuck closed. Brand new from caloric.

[kraft]

Temp sensor is stuck closed. Just checked voltage across r/b and  b/w wires feeding sensor and had voltage . Plugged in temp sensor to feed plug  and fan wont come on. Plugged temp sensor into voltage direct from battery and fan came on using the stuck sensor harness. cleaned all ground connections also.

[Mech]

Are you sure the voltage you are reading at the switch's plug has some current to it. If there's a bad connection before that plug, it could show voltage there, but only be enough to run the meter, not a fan.

I suppose you have a wiring diagram and have seen there's a fuse and a switch, and some wire connectors (inside the loom by the look of them) ,

Fuses can get bad connections, inside the fuse, or where they push in.

[kraft]

Temp sensor is stuck closed. Just checked voltage across r/b and  b/w wires feeding sensor and had voltage . Plugged in temp sensor to feed plug  and fan wont come on. Plugged temp sensor into voltage direct from battery and fan came on using the stuck sensor harness. cleaned all ground connections also. also just checked amp going to fan harness when fan running and is 5.16 amps when running top speed. The voltage across b/w and b/r plug is 11.87. Voltage across b/r  wire and a separate chassis ground to fan ground is 12.8 volts. there is a diode on the b/w wire in the harness, possible kaput?

[Mech]

You have two problems, one is a crook fan switch, and the other is a bad power supply to that switch.

A gauge can read a voltage to that fan switch when there's no load on the wire, but if there's a bad resistance somewhere in the power wire. the voltage will drop to zero when a heavy load draws more than the resistance can let through.

You need to back probe your gauge into the power wire connector to the fan switch. That means poke it's probe in on the wire side of the connector. Then with the key on, and the fan switch out of the circuit, there should be twelve volts or a little more showing on the gauge. Then if you plug in that stuck fan switch, the voltage will probably drop to zero, or near to, and the fan won't go. But if you then jump power direct to the fan switch as you have been doing, the fan will go.

If it acts as I say, then you have a bad connection somewhere in the fan fuse or holder, or in the splice in the wires that's somewhere between the key and the two fuses it controls, which are the fan and the ignition fuses.

 

[mikeexplorer]

There is a diode in the circuit. It is in the harness near the fan. You will have to unwrap the harness to find it

 

[kraft]

I found it, it won’t let current through. I jump around it and fan works as it should. I ordered a 25 amp diode from cat for the 500 machines. It should work. Thanks 

[Mech]

Errr.. that diode is on the earth wire..  When you put power into the fan switch straight from the battery the fan goes, but when you try to use the original power feed from the fuse it doesn't go. You don't need to supply a better earth to get it to go..   What does that tell you ?

It tells me that the problem is in the power feed, and it tells me the problem isn't in the earth end of things..

[kraft]

If I use the original power feed and a separate ground the fan runs fine. If aI use the original power feed and bypass the diode,the ground connection to the wire past the diode, works good.

[mikeexplorer]

That proves the diode is bad and needs to be replaced. 25 amp diode is more then enough and will work.

 

[Mech]

It seems the symptoms, and what does and doesn't work to get the fan to work,  have changed since the thread started..

[kraft]

Installed new fan diode, bingo, fan works as it should!