Working on fire engine AC (again)

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Dgreen
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Re: Working on fire engine AC (again)

Postby Dgreen » Wed Aug 01, 2018 8:58 am

I’m not sure what would be required for a refrigerant flush of the evaporator. Can it not be flushed with laquer thinner?

Just removed the compressor. It had a placard on it that said to use 500 ml of oil. Think that is half a quart. I’m stopping at half a sight glass.
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bohica2xo
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Re: Working on fire engine AC (again)

Postby bohica2xo » Wed Aug 01, 2018 10:13 am

Lacquer thinner works, but you know you need to get it all out.

I would side tap a can of brake cleaner & make an adapter fitting for a charge hose. Blow the whole can in to the evaporator, disconnect & blow air or nitrogen in behind it. A pretty big mess can come out of the suction line, so be ready for that.

For refrigerant flush you need a recovery machine & two recovery tanks. One is a "trash" tank, and will be forever. A little imagination and plenty of scrap hose assemblies will yield the fittings to make adapters out of.

You start with your flushing refrigerant in one tank. Connect to the liquid side of the flush tank with a manifold, and then to the liquid line on the evaporator. Connect the trash tank to the suction line of the evaporator via a second manifold. Connect your vacuum pump to the suction side manifold at the high side port.

Evacuate the evaporator & the trash tank. Close the high side valve to isolate the vacuum pump. Spin the valve open on the liquid side manifold, and let the liquid refrigerant in your flush tank fly through the evaporator to the evacuated trash tank.

When things equalize, close all of the valves, connect your recovery machine to the high side valve the vacuum pump was connected to. Recover the evaporator and plumbing. Disconnect the tanks.

To return your flush refrigerant to the clean tank, recover vapor from the trash tank. This can be done at your leisure.

My flush tank is full of recovered HC's mixed with R12 & some R22. It is great flushing agent, and rather than paying to dispose of it I just re-use it. R290 works excellent as a flush s well.

The trash tank over time fills with debris & oil. After years of doing this with the trash tank mine developed a good slosh. I pulled the valve assembly & dumped it out - it was not pretty.

My unwanted dreck refrigerant collection is at about 20 lbs. It is enough to do a 5 ton compressor burnout cleanup on the condenser in one shot. You could just as easily flush with pure 134a, or any other refrigerant you have an excess of.
Dgreen
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Re: Working on fire engine AC (again)

Postby Dgreen » Thu Aug 02, 2018 2:36 am

Thanks for the detailed instructions. I won’t be able to make it he refrigerant flush setup his time, but I will save your instructions and be on the lookout for an extra tank to be used as the trash tank. If I can gather up the correct fittings, I’m going to try the brake clean and side can tap method.

Got the clutch replaced yesterday. I didn’t get the screws holding the coil in place tight enough the last time I changed the clutch. They backed out and caused the clutch eat itself.

Thanks again and will post results when we get it flushed and back together.

Almost forgot, I drained 3 1/2 oz more oil out of the compressor to get the oil level right. That makes 7 1/2 oz that we’ve taken out.
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bohica2xo
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Re: Working on fire engine AC (again)

Postby bohica2xo » Thu Aug 02, 2018 7:45 am

Wow, a rolling oil well. Sounds like the last Firestone job I had to correct.

You can always side tap a can of keyboard duster to blow out a line or small evaporator too. Not cheap, but if the nitrogen bottle is 60 miles away it is worth it.

Refrigerant flushing works, but it is not for everyone.
Dgreen
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Re: Working on fire engine AC (again)

Postby Dgreen » Thu Aug 02, 2018 3:32 pm

It's up and running again. Mounted the compressor and got the oil level half way up the sight glass. Flushed the evaporator. It had a little oil in it, nothing crazy. Put on a new drier with no oil added to it and then vacuumed and recharged with 5 lbs 4 oz. on high idle high side was 235 low was 15. Temp outside was 85 and low humidity. Vent temp went to 43 briefly, but was running 47 to 49 most of the time. One thing that was different this time was I saw the low side go up to 40 a couple times then it would go back to around 15. I forgot to keep an eye on the oil level sight glass while charging, but when I was done, the oil level was almost to the top of the glass. Didn't quite understand that.

Thanks for all the help! This has been a work in progress. Hopefully this is the last we hear about this one for a while.
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Tim
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Re: Working on fire engine AC (again)

Postby Tim » Thu Aug 02, 2018 4:33 pm

That's a lot of oil removal! Glad it's working!
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Dgreen
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Re: Working on fire engine AC (again)

Postby Dgreen » Sun Aug 05, 2018 4:20 am

The label on the compressor said 500 ml of oil. By the time I had the clutch changed this time, I had lost most of the oil. Level was below the sight glass. When it was mounted I topped up the oil level to half way up the sight glass using an 8 oz bottle of oil and there was oil left in the bottle when done. Even if everything was completely empty of oil, 500 ml seems to be too much.
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bohica2xo
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Re: Working on fire engine AC (again)

Postby bohica2xo » Sun Aug 05, 2018 11:10 pm

500 cc's of oil is 16.9 Ounces. That is a lot of oil, even for a TM31. Sounds more like a system charge. I know the service manual says 500 cc's, but it also describes 220 cc's in the balance of the system.

So if someone before you replaced a compressor & dumped in 500 cc's You might have had as much as a Liter of oil in the system.

Keep an eye on it - you may need to drain some out of the compressor again. There is a gerotor oil pump in the back end of the compressor, and the manual says that anywhere on the sight glass is a good oil level.

The compressor manual also says that if you remove & replace the same compressor that you should put 350 cc's back in it after draining it - which kind of supports the 500 cc's as a system charge.

Just in case you don't have a copy
http://www.valeocompressors.com/media/brochures/TM31_servicemanual.pdf

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