Hello, everyone, I have an issue with a hydraulic driven AC unit on one of our trucks, for reference, this is a heavy duty road painting truck it has an auxillary Cummins engine that runs a hydraulic pump hydraulics go to Hydraulic driven AC compressor, hydraulic driven air compressor, carriages that roil in and out and hydraulic actuated paint pumps when the guys are out on a job, running the AC and all other hydraulic accessories, the AC being on, causes the hydraulic to become jumpy/ jerky, it spikes and drops the hydraulic pressure about 7times per second. and stops when the AC is turned off. what couild cause this? for reference, this a RedDot rooftop AC, with a remote mounted compressor.
Its hard to know without actually seeing the pumps and how they are driven, to know how your system works, but here's a guess. They don't have separate hyd pumps for the controls and the ac. So when either compressor makes resistance, you're going to have pressure drops. Only way to get around it, would be to go to a multi stage pump, or separate pumps. Take pictures of the pump on the engine, and the valves, and how its all plumbed, and maybe someone can give a little better advice. They run red dot A/C systems on a lot of the crane uppers, and they will draw hyd. from whatever circuit they are plumbed into. So usually they are plumbed to the telescope circuit, because that's the least used. And they don't cause spikes with the boom/winch/ swing. But the cranes have multi stage pumps. If everything runs off the same pump, its going to vary as the demand varies.
thanks for replying, i am not sure ill need a separate pump for it, this truck came from the factory with one hyd pump, this is a single stage pump, and it tied into the carriage roll in/out circuit
Just because they sent it out the factory door that way, doesn't mean it's going to work correctly, but it was probably the cheapest way to send it out the door
Is this a problem that was there from new or did it develop later on?
The way i see it, if the pulsation was from new means that it is poor engineering, and like above it may require a separate pump or be changed to engine driven rather then hydraulic. If the issue developed later then I would be looking at possibly high a/c pressures, or low a/c compressor rpms. I suspect the pump speed will be controlled via a flow divider rather then proportional spools.
THIS..........what Cliffy said. We need ALOT more info to go on. This a new vehicle or a well used vehicle?? Got an hour meter on the machine?? Was the AC working last year, then this year it crapped out?? Could be the AC was getting cold enough and 'someone' decided that a couple cans or more of AC fix from Autozone would be just the ticket........when it didn't need any refrigerant at all........and they just overcharged the compressor. so many questions...........LOL
this is a fairly new issue, i believe, i habent been working here that long, maybe a year. i know it hasnt been a problem since new, and this truck is well used, over 7,000 hours on the clock.
this truck is well used, over 7,000 hours on the meter ac was working last year, when this became an issue, and even with the pulsation the AC woould still work but the pulsation would affect other critical function of the hydraulics
is there an accumulator on the Hydraulic side that could have failed? low accumulator pressure can cause pressure spikes.
Ok.........first step. Put some gauges on the AC system high and low ports. Operate system, get high and low pressures after a 5 minute operation (you want the system to run a few minutes to get true pressures). Ambient air temp (outside air temp.......what is it??). I will assume this is an R134a system (refrigerant type). Is the condenser clean and the fan operating?? You need to have good air flow or if you don't, your high pressure side is going to spike up. If your high pressure switch isn't working on the system, then it will let it climb really high..........I've seen systems go to 400psi.....and then I shut it down. Condenser fan wasn't working, no air flow through condenser. At 400psi, I was just waiting for a big BANG!!lol
What David just said........just worked on a CAT 725 rock truck. Both accumulators were blown for the service brakes. The hydraulic system was "banging" (pulsating) every 1/2 second or so from the system trying to build up pressure and maintain it. Putting the body up with the hydraulics would really shake the cab from the pulsation. Like I said.........there is ALOT we need to cover and understand to get to the root of the problem. Look for any test ports on the hydraulic system you can plug into to get system pressures. You may need to plumb some gauges inline on the system. Can you get us some pictures of the hydraulic system.......that would help too.