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Thread: You know the feeling............

  1. #1
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    You know the feeling............

    Had one of the TM155's in last week to reseal the lift ram inside the top cover- the arms kept dropping overnight and we had lost one lower link catch so a lift arm snapped off by a drawbar was on the cards if nothing was done soon. Job was done- the piston seal has a fat oring underneath it which having gone hard and flat resulted in the piston simply dropping out of the cylinder- usually you should use an air line to blow it out where a good seal holds it fast.

    Once it was possible to run up and test the hydraulics and brakes I also tried the aircon just to see how cold it was ahead of doing a service check on the gas charge, it got off to a bad start when turning the AC knob and there was no clonk of the compressor clutch! Ah well something else to look at. First port of call was looking at the high pressure tube to see if this one had rubbed on the bonnet inner like the other 155. No all ok so connected the service machine up, the balanced pressure seemed to be a bit low so recovered the gas and found it was 1/3 full- perhaps just a low charge and the LP switch had kicked in? Vacuumed and charged it, no still no go. So now up with the roof and check the control potentiometer and the electronic thermostat once I'd got my head round the wiring diagram again, the manual has a misprint or two on the AC section, then a bit of testing and its not the trinary switch right next to the compressor but the electronic relay/thermostat up in the evaporator.

    Given that the relay is over 50 and the poteniometer another 30 it seemed a good idea to go for the conversion kit and back date it to a manual tube stat with simple mechanical switch and a short length of wire. Also while hooked up to the machine and around 6 years since the filter-dryer was last replaced it made sense to change the filter dryer, whip the compressor off to drain the oil and put a similar quantity + an oz for the new filter dryer of fresh oil into the compressor so it wasn't going too bad until loosening the 27mm low pressure tube nut on the compressor that there was that feeling that something wasn't quite right- the nut moved about 3/4 of a turn easily but then went really hard... locking solid. That familar feeling of the thread having picked up

    Luckily with a bit of thin oil on the thread it eventually came off and also the seal seat was intact but we had "lost" the first two threads. So it was time to start removing the pipe as well as the compressor and remove the offending bits of alloy out of the pipe nut thread





    Digging the alloy out with a seal pick didn't work so I knocked up a sort of bespoke "thread tap" using a JIC hydraulic fitting which has 7/8" UNF threads, the same as the aircon tube nut. In the lathe I trimmed off the taper nose and then bored it out to fit over the flange they use on the AC tube ends, next using the bench grinder I cut three flutes into the leading threads so I could use it as a crude thread tap! It took a bit of patience to get it cleaned out and then cleaning up the alloy thread on the compressor head.

    This can often happen when steel fittings have been on alloy threads for years, a slight spec of rust in there picks up a thread and then there is that familiar feeling....... Its good practice to oil the new orings when you fit them to stop tearing and to make a good seal, I also put a dab of the AC oil on the threads before winding the nuts on, not much but just enough to prevent this sort of thing happening. Ready now to refit tomorrow and regas. I've changed the orings up in the roof and at all other connections as none showed any leaks on a pressure test so hopefully we might of caught one that was leaking, if not hopefully the new oil in the compressor with its dye will lead us to any future leaks.....
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  2. #2
    Senior Member Footsfitter's Avatar
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    Re: You know the feeling............

    Finished it off today, the filter dryer and conversion kit from electric stat to old fashioned capillary tube stat came so once the dryer was on and waiting for the hour vacuum it was off with the old thermostat and potentiometer and after opening out the hole in the roof for the slightly bigger spindle I also took off a ridge so the stat will sit flat against the plastic and also allow the spindle to stick through a bit more, this allowed me to use the old original TM knob rather than the old 10 series style knob that came with the kit.

    I also did the wiring slightly different to the instructions in the kit which suggested running a fresh wire from the blower switch across to the loom and low pressure switch, I simply made up a couple of leads with the correct plug to fit the existing loom and the new thermostat switch and then at the other end using the old plug off the defunct thermostat/relay with just the two wires from the new switch and to the low pressure switch joined together to make the circuit.






    The old potentiometer (still works so will keep in case the other TM packs up!) and the short loom to join the new thermostat to the existing loom







    Making a link out of the old thermostat plug and wires






    The old electric stat sensor wire went in a hole in the end of the evaporator, the new capillary tube didn't seem to go in far enough so I did like the old traditional systems did - run it over the top of the core and then down into the core centre.
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