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Thread: Brrrrrr...........

  1. #1
    Senior Member Footsfitter's Avatar
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    Brrrrrr...........

    Seemed odd recently to be doing aircon work while it was freezing outside! The 755B challenger we have had just over 12months now was due a 1000hr service, while it was in I took the chance to sort out a leak we had on its Aircon. Putting some dye in it last autumn nailed where the small leak was and the top up of gas lasted the season out.





    Splashed out on a new service station last year after the dealer who supplied the Challenger used one to fit a new compressor under warranty that had a shaft seal leaking. I'd been looking for some time to upgrade from the old kit and was impressed with "The Cube" as its called. It also dragged us into dealing with NCG's - Non Condensible Gases. With the old kit when time allowed we could use a little tool to calculate the amount of NCG present in bottles of gas and bleed them off so they don't get put into the AC system, now with this machine every time gas goes into it you have to deal with it by default. NCG's can build up in the condenser where they sit "blocking off" part of the condensers capacity to transfer heat- a bit like putting a board infront of it and blocking off/reducing its output.

    The printout shows that 350gms of gas had escaped. Dealing with the NCG's involves dialing into the machine to find the recovery bottle temperature, you look it up on the chart which then tells you the correct pressure you should have in the bottle, 99% of the time it will be higher so in the slot just above the chart is a ringpull to vent the unwanted gas so while watching the pressure gauge you bleed it off, now its possible to just feel/hear the slightly different sound when you get to the target pressure as the undesirable gases run out and refrigerant gas starts.











    Heres the pipe that was the cause of the gas loss- a steel tube in a sort of wide-shallow U shape that fits on the HP outlet and brings the flow forwards to the filter dryer and condenser. There was also some possible leakage from the hose that is next in the circuit. The last 3 pics show round the back of the cab where the Evaporator is. Although we flushed it before the new compressor went on 12 months ago, there had been some oil loss and I wanted to change the oil to the type I now use and also work out exactly the right amount so that when finished we had the right amounts of everything in the right places. Its a bit of a fiddle getting the two connections undone but in order to flush I need to get the metering orifice out- you can see I cheated connecting up by using the old compressor tube to get the flushing connectors on easier because of the handy shape putting the adaptor out where I could access it easier. Capped pipes show that they have been flushed and are sealed until we are ready to reassemble.
    Last edited by Footsfitter; 10-02-18 at 08:11 AM.
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    Senior Member Footsfitter's Avatar
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    Re: Brrrrrr...........

    Heres the flushing kit. Solvent is put in the blue tank and dry compressed air is used to blast it through sections of the system in a pulsating mix of air and liquid which is then collected in the bucket. This machine was easy because both times there had been no compressor or filter-dryer desiccant failure, but it still requires a systematic approach to get the system clean. I like to keep the bucket clean so you get a true indication of what if any debris comes out. As part of the process the filter-dryer and accumulator are binned, as is the metering orifice tube- its only a couple of quid and gripping it to extract it out of the tube it hides in can rough it up a bit. The former two items can't be flushed and contain some oil so have to go and again they are not that expensive.

    Once the flushing is done, the system components are blown with dry air for long periods to remove all traces of the cleaning solvents








    Here the compressor having been drained is about to get refilled with the correct amount of fresh oil already dyed, then once all the system is coupled back up a bottle of OFN - Oxygen Free Nitrogen is used first to purge the system of air and then to pressure test the system to 10-11bar. This was left overnight and we were surprised to find that there was an issue with the new hose leaking which was quickly rectified. Next the system was vacuumed for 10 min to de-gas the oil and check the system held a vaccum ok, then it was vacummed for an hour to remove all moisture and leave the system ready to charge with 2.1kg of gas.

    The last few pictures show a change in the routing of the new hose and a modification to support the hose/steel tube- it looked to me that with the compressor being part of the engine shaking on it rubber mountings and they way the hose was rigidly clamped the poor old steel tube was being forced backwards and forwards stressing the simple flanged oring connections. I drilled and tapped the compressor bracket to take a bolt for securing a small steel bracket that the hose fitting could be held rigidly with a simple hose clip.








    Having done all this it was then time to test the system which because of the cold weather was a bit academic! But running around with the infra-red temprature gun showed that the gas temperatures were indeed fluctuating as they should in the correct areas so fingers crossed it will be all ok when we do get some proper warmer weather!!
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    Senior Member wr.'s Avatar
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    Re: Brrrrrr...........

    Very interesting. A chap from Hereford come to the farm to do ours when we have a couple that want regassing.
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    Re: Brrrrrr...........

    Quote Originally Posted by Footsfitter View Post
    Heres the flushing kit. Solvent is put in the blue tank and dry compressed air is used to blast it through sections of the system in a pulsating mix of air and liquid which is then collected in the bucket. This machine was easy because both times there had been no compressor or filter-dryer desiccant failure, but it still requires a systematic approach to get the system clean. I like to keep the bucket clean so you get a true indication of what if any debris comes out. As part of the process the filter-dryer and accumulator are binned, as is the metering orifice tube- its only a couple of quid and gripping it to extract it out of the tube it hides in can rough it up a bit. The former two items can't be flushed and contain some oil so have to go and again they are not that expensive.

    Once the flushing is done, the system components are blown with dry air for long periods to remove all traces of the cleaning solvents








    Here the compressor having been drained is about to get refilled with the correct amount of fresh oil already dyed, then once all the system is coupled back up a bottle of OFN - Oxygen Free Nitrogen is used first to purge the system of air and then to pressure test the system to 10-11bar. This was left overnight and we were surprised to find that there was an issue with the new hose leaking which was quickly rectified. Next the system was vacuumed for 10 min to de-gas the oil and check the system held a vaccum ok, then it was vacummed for an hour to remove all moisture and leave the system ready to charge with 2.1kg of gas.

    The last few pictures show a change in the routing of the new hose and a modification to support the hose/steel tube- it looked to me that with the compressor being part of the engine shaking on it rubber mountings and they way the hose was rigidly clamped the poor old steel tube was being forced backwards and forwards stressing the simple flanged oring connections. I drilled and tapped the compressor bracket to take a bolt for securing a small steel bracket that the hose fitting could be held rigidly with a simple hose clip.








    Having done all this it was then time to test the system which because of the cold weather was a bit academic! But running around with the infra-red temprature gun showed that the gas temperatures were indeed fluctuating as they should in the correct areas so fingers crossed it will be all ok when we do get some proper warmer weather!!
    Could you give me a little help on pump hydraulic flow on the average Challenger? Most modern tractors are around 90 litres, but we have a customer using a challenger on our mill mixers, wreaking all sorts of havoc with too much horsepower. Probably done some hydraulic damage as wel.
    Thanks in advance,
    Jack

  5. #5
    Senior Member Footsfitter's Avatar
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    Re: Brrrrrr...........

    Quote Originally Posted by Jack_Caley View Post
    Could you give me a little help on pump hydraulic flow on the average Challenger? Most modern tractors are around 90 litres, but we have a customer using a challenger on our mill mixers, wreaking all sorts of havoc with too much horsepower. Probably done some hydraulic damage as wel.
    Thanks in advance,
    Jack


    Hi Jack,


    having the right model would be a help as there's a lot of them!

    Although |I would of thought that they should be using the flow screwed down to match the mill's flow requirement and if there are any motors involved the usual rule of thumb is to use the spool lever in the forward detent and push it forward into float to stop flow (allows motors to slow to a stop). The other problem is if they need a free flow return and are doing something wrong?



    Heres a snip from a MT755B brochure which is our machine-







    While this I found this for the later MT700E series








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