AC problems on 272C Cat

[txbrushbuster]

Since I bought this machine new I have had on going AC issues. It has been in the Cat service dept many many times along with service calls. Lost track of how many. It usually sits there a week so when I call they say oh the ac is working fine. I pick it up & low and behold it does work, untill I unload it the next day on a job site. Two years of this and of coarse now it is out of warranty. Something is telling the compressor not to come on. I think when I take it in they know how to make the conpressor come back on but like I say it doesn't last. I had it working for a short while after replaceing a thermastat swich but now I don't think I'm even getting power to that switch.
It's going to be another long hot summer if I cant find some answers because Holt Cat either cannot or will not fix it. :Banghead

 

[KSSS]

Since I bought this machine new I have had on going AC issues. It has been in the Cat service dept many many times along with service calls. Lost track of how many. It usually sits there a week so when I call they say oh the ac is working fine. I pick it up & low and behold it does work, untill I unload it the next day on a job site. Two years of this and of coarse now it is out of warranty. Something is telling the compressor not to come on. I think when I take it in they know how to make the conpressor come back on but like I say it doesn't last. I had it working for a short while after replaceing a thermastat swich but now I don't think I'm even getting power to that switch.
It's going to be another long hot summer if I cant find some answers because Holt Cat either cannot or will not fix it. :Banghead

I have had this issue on an excavator. The valve that is supposed to shut the hot water off was actually getting bypassed and not sealing and actually running the heat and canceling out the ac. Only did it when working the machine at idle, ac would seem to work fine. You might have a similiar issue.


YellowDog who makes an appearance here every so often had the same issues with a 272C running a mulcher. CAT ended up taking the machine back. He had other issues as well but the AC and a leaky cab were major issues.

 

[jrtraderny]

I've got a brand new 247B2 that the AC wouldn't work on.
Cat tech came out and checked it out said nothing's wrong and now it's working, go figure.
jr

 

[Per Eriksson]

Do you know if they have had to add R134A to the system to get it working any of the visits to the shop?

A system that's sealing when doing the vacuumtest but not when running sounds likely for your machine if that's the case

 

[Per Eriksson]

It's easy to check the 2 pressure switches also,

the low pressure switch should be closed if there's enough R314A, Green wire 689 and purple 597

High pressure switch also closed if all is ok.
597 purple and A509 pink,

Follow the lines from the compressor and they should be located where they end.

these provide a ground path to a compressor clutch relay.
4 pin connector,

1 signal from the pressure switches 589 Green
2 chassies ground 200 black
3 output to the clutch E554 pink
4 +12V supply from the AC switch in the cab 520 white

These systems are so simple a trained monkey should be able to get them working, one can wonder what the techs at Holt do?

 

[txbrushbuster]

So how can I tell if the switch is open or closed? I can only seem to find a plug not a switch that I can trip open or closed.

 

[txbrushbuster]

It has not needed more coolent.

 

[Per Eriksson]

There are no external buttons, the switches just sense pressure in the ac lines and close or open contact internally, you'll have to measure across the terminals with a multimeter to find out if they are open or closed.

With the multimeter you can also check for correct voltages.