Bobcat t650 a/c troubleshooting

[davejo]

I borrowed a 2013 model and found the a/c inoperable. Owner claims it worked last season. Now i'm learning about the system and working my way forward.

Initial behavior was no green light when a/c toggle flipped upward. Watching the compressor, the clutch engages and spins for about a second a short time after the switch is flipped.

Fuse is ok, swapping working relays made no difference. 45 psi in the low pressure port at rest. I have the white wires to the toggle switch jumpered. I have the wires to the pressure sensor on the drier can jumpered. I'm still getting a brief moment of compressor spin and two blinks from the tiny module under the cab.

Next step is to check voltages at my jumpered connections and downstream? The clutch is obviously getting some sort of voltage.

The connector to the A/C clutch is in an impossible position so am thinking of just piercing the feed wires with a needle to meter them.

 

[Arny L]

What I normally do is jump the compressor relay 30 to 87, this should supply 12 v to compressor clutch, it should run continuously. Set temp control to cold and see what happens. If no cold air, then system is empty. If clutch is getting 12v but wont run, then I would suspect electromagnet, or rust build up on clutch apply surface.

 

[davejo]

I jumpered the relay. Every 20 seconds, the clutch is energized for a half second before releasing again. The module is blinking twice except for the moment when the clutch is turned on, then the light is steady.

Voltage at relay is about 12.1 volts and it drops a half volt each time the clutch is actuated.

 

[Arny L]

Interesting, the repetitive 20 second intervals sounds like pressure cycle switch trying to activate, but with no turning compressor, there is no pressure to cycle. Would the module be controlling the ground side of clutch circuit. Bad ground would try and start compressor then fail. You have to check voltage right at compressor I think, if you got a strong 12v that doesn't drop out when activated, then its either compressor pouched, or bad ground. Scan tool on hand!!

 

[davejo]

Yes the every 20 seconds aspect makes me wonder if whatever brain controls the system is activating the circuit then noticing the voltage change or amps and finds them not to its liking. I heard that two blinks means open clutch circuit or shorted clutch circuit or clutch over voltage.

The location of the compressor is a nightmare, I'm hoping the problem is anywhere else but there.

 

[heymccall]

45psi at rest on a 70° day is indicative of low charge of refrigerant.

 

[davejo]

There is a switch next to the drier canister next to the radiator stack. I unplugged it and installed a jumper. I'm under the impression that this is a pressure switch and that it should be fooled into thinking there is enough refrigerant to allow the compressor to operate. Is this correct?

I will definitely add some 134 on your advice

 

[ozarkag]

Yes the every 20 seconds aspect makes me wonder if whatever brain controls the system is activating the circuit then noticing the voltage change or amps and finds them not to its liking. I heard that two blinks means open clutch circuit or shorted clutch circuit or clutch over voltage.

The location of the compressor is a nightmare, I'm hoping the problem is anywhere else but there.

The little temp sensor module is the "brain" that is cycling. We keep one on the shelf if that tells you anything. . .
Two blink code for open circuit, yet compressor kicks in momentarily, so. . .likely a bad or failing module. A lot easier and cheaper to replace than the compressor. IIRC a good compressor clutch only draws minimal, under 2? amps. A high amp draw will trip the module as well.

And 45 psi at rest should get you running and cooling. Check and top off on a good warm day.

 

[davejo]

Local dealer let us borrow a module and it gives us the same results. If the windings in the electromagnet start breaking down, would it draw more amps, more of a voltage drop etc?

 

[heymccall]

I'm a little slow here, but, if you jumpered the relay, wouldn't module be offline?

Even my cheap multimeter has an amperage mode for up to 10 amps. Why not 12v connect directly, with one leg going thru an ammeter, to the compressor and measure draw /verify function?

Done with engine running, you could see pressures also.

 

[Arny L]

Wow, that's a dealer with a heart of gold, Nobody I know ever would let you try an expensive electronic module without paying for it. And let you return it, double Wow. It depends on how the magnet fails, if it shorted to ground, obviously it should blow a fuse, but you said no fuses blown. AC compressor is usually fused at 20 amps, But actual running amps,(depending on size of system) can be any were between 3 and 4amps. But the highest amp draw would be initial start up. Which is right when yours seems to be failing.

 

[davejo]

The module must be downstream of the relay. Evidently the dealer has a module just for testing the ones they get in for problems and that is what we borrowed. Very generous.

The wires that feed the clutch pass behind the engine. The connector is zip tied below the turbo out of sight and barely within reach. The wire joins the harness and goes to a six wire connector to the left of the engine about 3 feet deep in the engine bay.

Once we establish access to the wires we can do more testing. If hotwiring the clutch results in cold air from the vents, that might end up being the permanent solution until the clutch ultimately fails completely, if that is what is actually going on here.

 

[ozarkag]

Here is the manual page on the EDT for future reference.

 

[davejo]

Thank you thats excellent. I was able to get the zip tie cut and unplugged the a/c clutch. 3.7 ohms resistance between the leads.

but when I tried to hot wire the leads to check amp draw, the clutch closed when simply touching voltage to the black lead only. how is the coil pack shorted to ground? isnt it encased in plastic or potted? maybe the red wire is chafed and rubbing metal back up underneath the clutch pulley. The clutch doesnt close when voltage is applied to red wire only.

I guess i didn't think to test each wire for short to ground with ohmeter. They should both be shorted to ground if my chafe theory is correct. That's next.

 

[Arny L]

I would think red wire is powered 12v when key is on through relay, and compressor on off is controlled on ground side by EDT. So touching 12v to red wire does nothing without the ground side. Are you sure its not the EDT.

 

[davejo]

I'm 99.9% sure its the clutch coil wire or windings. According to the pdf posted, i should be getting 3 blinks for a shorted coil, though.

With the connector right by the compressor unplugged, both red and black wires feeding the clutch coil have continuity with the engine block etc.

When I think of a magnetic winding, its just a coil of a single wire with one end connected to hot and the other to ground. Polarity shouldn't even matter but since there are two wires present, the ground should go through the wire instead of the compressor body itself. I think this is reflected in the wiring diagram. One wire labeled SGL, the other GRD.

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It looks like the coil is hermetically sealed so the wires shouldnt have continuity to anything but eachother.

 

[Arny L]

I had an old AC compressor laying around, so I tested the one an only lead going in to coil, and it also showed continuity to compressor body, and I know this coil is good, so it doesn't mean your coil is shorted.

 

[davejo]

45psi at rest on a 70° day is indicative of low charge of refrigerant.

Part of my slow progress was due to a broken cab lift strut, couldn't lift it up and down on my own to start and stop the engine etc.

Apparently, I know just enough to be dangerous and my idea of logic doesnt sync with bobcat logic.

I got a new strut installed and a new toggle switch for the a/c. I installed them and took out my pressure switch jumper just in case the switch is non binary. Started the engine and measured the pressure, it dropped to almost nothing then the clutch disengages a second later. The light then blinks twice for 20 seconds and the clutch engages again.

Each clutch engagement lasts slightly longer and longer until it sucks in a small can of 134 and now blows cold air.

Perhaps the manual should state that two blinks can also mean low refrigerant, unless I still have some lingering issue tripping the EDT

Learned a lot and appreciate all the help!

 

[davejo]

Borrowed the bobcat yesterday and no cold air again so back to the troubleshooting.































Here's the wiring diagram for the time being

 

[Vetech63]

Seems like you have a refrigerant leak in the system. Do you have gauges and a vacuum pump?