Alt AUX alarm on standby operation

[jakemigz]

I got a Alt Aux alarm on standby operation there is no signal on MPL3 going to excite wire of the alternator, but on Diesel operation there is a signal. Anyone knows what is the problem?

[jakemigz]

I forgot to mention this is for CARRIER SUPRA 50 Series

[DaButcher]

Bad oil pressure switch can cause the alarm

[123smc]

Hi, could you give more information on the unit 450,550,750,850 or 950. Single temp or multi temp? And the age of the unit. It could be the alternator isn't turning fast enough, clutch sticking or loose belts?
I've had one recently with chaffed wiring at the alternator resistor.

[jakemigz]

What happening is once I plugged it on electric and switch it on pressed the standby switch the alt aux alarm appeared in the cab command the unit won't start because of this alarm i think this alarm is a shutdown alarm if selected ON in CNF 16 in the microprocessor configuration. I have encountered this problem with Supra 450, 750, 950MT, there's no positive signal from MPL3 going to the alternator excite wire, but when I switch it on to diesel operation there's a positive signal from MPL3 to alternator excite wire. It saying in the service manuals that ALT AUX will generates due to lost of signal to alternator excite wire the battery will not charge without the signal so it will shutdown the unit on diesel operation.

[jakemigz]

All the belts are fine and tight and the fridge is not that old.

[jakemigz]

Thanks Dabutcher, I will try to check the oil pressure switch, maybe this switch triggered this alarm that's why there is no signal from the microprocessor L3 on standby operation.

[IRMechanik]

is the unit not starting because of the alt aux alarm or is the unit not starting and causing the alt aux alarm? Is the contactor pulling in? Generally a no start in standby will give a sby mtr code if the reset it tripped or if you've lost power completely it will say no power. But if you've lost 2/3 legs or the motor is open or the contactor is not pulling in you'll still have power to fool the voltage detect and the overload won't trip so you get a alt aux alarm.

[jakemigz]

Hi IRMechanik, the unit is not starting because of the active alt aux alarm, once I switch it on to standby it won't starting.

[IRMechanik]

Check to make sure CNF16 is off, then alt aux should be an alarm code not a shutdown code. On newer units this is default on. Check your contactor for power. On startup the unit should shift to heat then pull in the contactor. After the contactor is engaged if the motor does not start it will throw an alt aux code, there isn't a long delay before the alt aux code sets.

[UT2SeanWhite]

I am having similar problems with my Carrier Supra 750 mt. I have found that the digital display screen(little black box with the on/off switch) wouldn't even turn on, but once i switched it out with another, the screen lit up and the unit turned on. I have about 4 other digital displays that are dead, and without the "brain" (the little black box) the machine won't work. I wonder why so many of the digital displays are dying. Could it be from improper voltage or maybe spikes? Will the unit operate differently when it is tapping into fuel instead of electricity? I may need to check the generator that the unit is pulling its source from to see if the HZ are correct and voltage. Any suggestions? Before i switched the digital display out, i would push in the contactor int he micro-processor box and the unit would kick on, so i feel that it wasnt mechanical but electrical. again, any suggestions?

[Top_cat]

UT2seanwhite- are you saying the cab control dies after being run on standby? Or is it failing after road use too?

I'd be checking my cab control and the plug it gets its feed from in the control panel, I've had water in the plug which connects to the processor loom which feeds the power to the cab control. Also check you processor.

Hope this helps. Good luck!

[Top_cat]

I meant can control loom*

[Top_cat]

I meant cab control loom*

[UT2SeanWhite]

I came into another problem with this particular unit. Last night I and a mechanic had given the unit an oil change and new filters because the unit would say ENG OIL. After all was said and done, i went to turn on the unit and the control panel went nuts. there was a mass of flickering and clicking from inside the micro-processor box. I would wiggle some wires and whether it was coincidence or problematic, the clicking coincided with the control panel. I left it alone as it was going on 7 pm and i had been raking my brain all day with it. I awoke in the morning to try to figure more stuff out and I had it back on Standby instead of Road. The unit did the usual start-up alarm and as soon as it was about to start up it shut off and the alarm went off again and the display HIGH PRES come on. I read the pdf manual i have and it said that the suction pressure in the compressor was too high. It was 61 degrees in the box at this point. Later on in the day, i went back and tried to fire it up again and it kicked on, with no problems. It was 88 degrees in the box when i kicked it on. I shut it off almost right after i kicked it on and i wanted to see if it would kick on again, and it did. I have not shut the machine off since and its been running for about 45 minutes now. Weird huh? I forgot to mention that last night when i was playing with the wires and i was getting the clicking, i could hear the perf board with all of the little black boxes on it, one of the black boxes was clicking. Im guessing that those are a kind of capacitor, but i couldnt see any sign of the "uf" symbol on it. Any suggestions?

[UT2SeanWhite]

what is the cab control loom? I wish i had a visual breakdown of every part of this machine. I need to learn how to get these things up and running. oye! So what is the cab control loom?

[Top_cat]

High press alarm will display if there is a bad earth connection. Check your live and earth connections. Check your voltage on the main fuse in the control panel. Fit gauges to eliminate a legitimate pressure fault. It sounds to me like a voltage fault. Unplug the micro processor plugs and clean the pins.

Just thorroughly check the power feed from the battery up to the fridge. On the engine side check the voltage on the positive and negative studs.

Let me know how u get on!

[djbe]

It sounds that you have correctly diagnosed a problem with the in cab controller or "little black box".
I would very much doubt that the failure is due to improper voltage or spikes, this is more likely to affect the microprocessor.
Just bad luck I suppose,although Thermo Kings are harder wearing generally so maybe a Carrier problem?