Hydraulic oil temp and pressure sensors

ancomcabs · May 7, 2012

Is there a way to test if the sending units are functioning properly. My hydraulic light on the 630 does not come on at all, even with the engine off and the key on, checked the bulb and it's good, and while I have the machine mostly appart I'd like to replace the sensors if they need it but they are too much money to do just for the heck of it.
I guess an other question would be does anyone have another source for these sensors, one was 50 and the other 150

Tazza · May 7, 2012

To test you just need to see if the NC connections are closed when the machine is off, if its not, you need a new sender.
The temp one, i tested mine by taking it out and using a gas torch to warm it up. Use a multi-meter and slowly bring it up. I can't remember what temperature it closes at though, but should be arounf 100c.

donald73d · May 11, 2012

No one said parts for the Bobcat are cheap. I would ground the temp sender connection or the NC connection on the pressure switch and see if the light comes on. Maybe you are not getting 12V at the light. The senders supply a ground rather than a +12V. Does the hour meter work? It is on the NO connection of the switch. There may also be another sender for the filter in the engine compartment. Its a clogged filter sender. I would say the pressure and temp of the hydraulic system is pretty important. Did you check the engine oil pressure light/sender? I replaced both bulbs, all 3 gauges (sawdust in them) and the charge pressure sender on my 1990 843B. Do you have a manual and a DVM? The oil pressure switch for my pickup's Cummins diesel is about $250 at the dealer. Its fancy and gets +5V, -5V and sensor. So don't feel too bad at the high cost of parts for a Bobcat.

ancomcabs · May 11, 2012

donald73d said:
No one said parts for the Bobcat are cheap. I would ground the temp sender connection or the NC connection on the pressure switch and see if the light comes on. Maybe you are not getting 12V at the light. The senders supply a ground rather than a +12V. Does the hour meter work? It is on the NO connection of the switch. There may also be another sender for the filter in the engine compartment. Its a clogged filter sender. I would say the pressure and temp of the hydraulic system is pretty important. Did you check the engine oil pressure light/sender? I replaced both bulbs, all 3 gauges (sawdust in them) and the charge pressure sender on my 1990 843B. Do you have a manual and a DVM? The oil pressure switch for my pickup's Cummins diesel is about $250 at the dealer. Its fancy and gets +5V, -5V and sensor. So don't feel too bad at the high cost of parts for a Bobcat.

Hour meter works and both bulbs have been replaced
Taz I'm not sure what you mean by NC connections?

donald73d · May 11, 2012

ancomcabs said:
Hour meter works and both bulbs have been replaced
Taz I'm not sure what you mean by NC connections?

The charge pressure switch has a NO and a NC connection. Normally open and normally closed. The normally closed is for the low charge pressure light and the NO is for the hour meter. Normal being engine not running. Its marked on the switch if you wipe it clean and look carefully.

ancomcabs · May 13, 2012

donald73d said:
The charge pressure switch has a NO and a NC connection. Normally open and normally closed. The normally closed is for the low charge pressure light and the NO is for the hour meter. Normal being engine not running. Its marked on the switch if you wipe it clean and look carefully.

Thanks for the explanations but I'm still a little confused, no doubt exposing my ignorance here. The two sensors I'm talking about each have one wire coming off the back and they thread into the side of the port block. If I removed them is there a procedure I can use to test them off hte machine before I put it back together?
Thanks

donald73d · May 13, 2012

ancomcabs said:
Thanks for the explanations but I'm still a little confused, no doubt exposing my ignorance here. The two sensors I'm talking about each have one wire coming off the back and they thread into the side of the port block. If I removed them is there a procedure I can use to test them off hte machine before I put it back together?
Thanks

One you would need to pressurize with say air and measure with an ohm meter and the other with heat. In my 843 the charge pressure switch has 2 connectors, but certainly it may be different on different machines.

Hydraulic oil temp and pressure sensors

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