CAT 320E intermittent electrical on AC/C

Greetings Friends of the Forum! Hope you are all staying Covid-19 safe, families and all! Got a little problem on a machine that is one of those "now you see it, now you don't" types. It also has a couple of features that I find no logical connection between. This machine has a nice digital display, with a rear-view camera. Sometimes , when the A/C is powered up, by the power button on the A/C control panel, the display blanks out. It's seemingly random. The dealer spent two days with no success, nor any recommendation. So it's back in our hands. First order of business, after an extensive physical examination of the wiring, fuses, etc., I need a schematic, of at least the A/C block, and one of the control console if it is a separate section. It would first strike me as a poor connection or a bad ground, since the operators say it happens more when they are on rougher, firmer terrain. Also, oddly enough, when the A/C is running, though it is charged sufficiently and the compressor is definitely engaged and running, there is no cold air. There is until the "blackout". The A/C control console also blanks out. Before it does, however, all the display icons are there, and show modes correctly. If anyone could share some schematics, I'd be grateful. Thanks Pertinent information:

I sent you two schematics. The aircon electrical is separate from the main machine electrical.

Thank you Nige. I felt there was a fair chance there would be a section dedicated to the A/C. Much appreciated!

The C and D series modules also had their own diagnostics and there were different control modules that had different ways of getting into there. Maybe someone here might have access to material on how to get that information.

John, are you referring to the A/C control modules? If so I'll need the diagnostic procedure used on the "E" series if anyone has it. I'm really trying to see where and how the A/C circuit and the "digital dash" (including the video display), are connected and which one is at fault causing the screen blackout and killing the A/C. So I'll spend some time this weekend studying the schematic. Surely there must be something in common.

Intermittent faults can be a real pain to troubleshoot, so no firm answer but a few random pointers; If you can catch the problem as it's happening, back probing a component with a good power or ground at the appropriate pin can give some direction. Notice that the wipers and hour meter share a common ground. Do they also stop working? It can sometimes help to rig up a temporary test light in the cab so the operator can tell you if it goes on/off when the fault occurs. If you're desperate to actually do something, check/redo the cab-chassis ground strap.

Thanks, Cmark. Having been into electrical/electronic work a while, I'll have to say that poor grounds are probably the most common faults I've found. Lots of cables/terminals appear fine, and one thing that I guess I don't understand is the fact that so many techs insist on using strictly hi Z meters to check continuity. I know they are capable, and some have a dedicated setting for it. But they simply don't "load" the connection enough to catch them all. Some meters are fooled because even a bad ground will carry enough current to read ok on them. I typically use a older analog meter such as the venerable Simpson 260 series with its 20k impedance. Or if desperate even a Hi-Pot tester and treat it as a leakage test. But it's usually easiest just to do a quick test, look for signs of heat (high R+ high A= high T), and just break the connection and clean it, or sometimes replace the lug if it looks bad. I've found lots of charging circuit issues that way. Electricity is funny stuff sometimes. I'll check and probably remake that ground connection out of safety. I try always to put some sort of protective coating on the connections I remake. I think it pays off.

Yep, when you're chasing suspect power and/or ground, a 21w stop light bulb and two pieces of wire will be more reliable than a DMM.

Tony Wells said: John, are you referring to the A/C control modules? If so I'll need the diagnostic procedure used on the "E" series if anyone has it. Click to expand... The C and D series AC control modules had their own diagnostics and you accessed them in the old manner of holding two buttons down at the same time. Problems was that they were different buttons depending on which module Cat happened to pay less for in the production runs at any particular time. I'll scan and upload what I have in a bit.

Hopefully this works.

John, thank you. That should help at least eliminate a few things. I'm glad it has self diagnostic capability. I know it's their prerogative, but at times it's a bit frustrating to have all the sophisticated systems on the machines and reserve such diagnostic ability for only the manufacturers themselves. In theory, it seems if they sold as much equipment as they wished they could, there is no way they could keep up with all the after sale service. They would have to either staff up, or risk irate customers with expensive equipment sitting idle waiting on a tech to arrive to handle the diagnosis. I'm afraid it is already borderline on that front anyway. OK...that's just my POV, and not related to this thread. I'll post any results from that testing.

I'll have to beg the court for a recess. Meanwhile the machine sits. I'll have to come back to it. Another problem interfered.

I wondered how you were getting on.

Well Nige, I went to a bad hose on a little dozer that was pumping oil out as fast as the guys could pour it in. Luckily we have a hose supplier here who will make them while I wait, but the machine was a ways off, so by the time I managed to untangle it, get a replacement made, and get back out to the machine.....here we are. Meanwhile I got a call on a couple of sheepfoot packers that have been run through the butcher shop, electrically speaking. I just don't know what gets into people. One is an Ingersol, the other a brand I'm unfamiliar with. Zahn or something like that. I haven't looked closely at it yet. The guys have the dash all opened up and tell me every safety has been bypassed. But the turbo was a miracle. I'd guess 5mm shaft clearance where the bearing used to live. Just to crank it and move it into the shop lost a liter and a half of oil. The new one came in today, but of course the mount was different. I think we can salvage that situation, but the electrical is a mess. The Ingersol, on top of the wiring, I suspect has a vibratory motor issue, or a pump. Have a flow meter coming in to see if the pump is any good, or it's the motor. I'm about to post a request for a schematic. Half the gauges are replacements, and there are about a dozen wires clipped and hanging in the console. Push-to-start has been rewired to a rotary ignition switch. Etc....But I'm thinking that the solenoid valve for the vibratory pump flow is not working. It has continuity, but due to the wiring, I'm not sure where it is powered from. There should be a "defeat" feature so you can't run the vib motor while stationary, but I can't "see" it in what circuits are remaining. I wouldn't be surprised if it had been bypassed. Biggest problem is that the owner has already committed to moving both these to a job in Alabama.....Tuesday. And this is a 3 day weekend. I'm afraid he is not going to get what he wants. Particularly on the suspected vib motor or pump.

Hello sorry to drag this up. I have a 320e Naz here with similar issue of power on with key and boots up ac controller could be flashing, camera in display flashing, wiper not operational but switch on work light and could all start working. Could easily work if cycle ignition. All happening when machine static. Have found that when its occurring only 11 volts going to ac controller but if you cycle ignition it could come up to 24v. Am a little stumped.

Poor/intermittent ground somewhere.? Dodgy key switch.? Do you have an electrical schematic.? Need a full S/No not just the prefix to find the right one.

Ya possibly tested the power with independent ground and it was still bad Naz02060 Could be bad key switch but I would need one to eliminate

Found the problem its 213-0772 main relay behind fuse bord faulty. Its a expensive part also

declan rafter said: Its a expensive part also Click to expand... The price of those relays usually makes your eyes water.

Nige said: The price of those relays usually makes your eyes water. Click to expand... You’ve been trying to get this guys piece of equipment fixed for 6 years? You must charge by the hour…