7.5 ton Trane package unit

fluffybunnysuiAugust 1, 2007

I could use a little help from all you commercial guys out there that work on a lot of Trane package units. I was called today to look at several units ( 2-15 tons, 1-12.5 ton & 1-7.5 ton). I have done some work on their residential lines but not on the commercial stuff.

Here's what i have. 7.5 ton package unit, all electric, 230vac 3 phase, 2 circuits, one 4 ton & the other 3.5 ton. Unit was not running except for the blower. Pulled the door off, installed gauges on both compressors, checked voltage (had it) checked transformer (had 24vac out), t-stat set to cool. Working with a lot of York's, i know if they have problems, the board shuts the compressors off & they stay off until you reset the breaker. That's what i did here. Turned the breaker off.... then on. Waited about 5 minutes, compressor #1 came on, along with cond.fan. A few seconds later compressor #2 came on. After about 10 seconds, head pressure pegged my gauge, and the unit shut off. No frosting in that short of time that i could see. Back to where i started, but i know i have a restriction somewhere.

This is what I'm unfamiliar with: I couldn't find a TXV or a flow-rater anywhere. Looks like both liquid lines come straight out of the condenser, thru 2 extruded dryers (gonna pull them off tomorrow) and straight into the evap coils header pipe. Did not see any cap tubes, nothing. Am i missing something? Are they using the overall length of the liquid line as a cap tube?

Any help would be appreciated.

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You might want to post your question on HVAC-Talk.com. The pros there can be a little rough on you but it may be worthwhile.

    Bookmark   August 1, 2007 at 9:28PM
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post model numbers if you have em.
Im pretty familiar with trane rooftop units. if its the ones im thinking of, they have multiple fixed orifice metering devices in the liquid header right at the evap coil. (i.e.. if the header has 6 lines coming out of it, you have 6 orifices.) kind of a bad design in my opinion. dont understand why they didnt just use a txv-distributer-feeder tube setup.
we've found units with plugged orifices and we just changed the entire header. (its a pain in the rear)

high side pegged the guage?
is your condenser coil clean?

stupid question but, you DID have the compressor access door on when you fired up the unit didnt you?

leave that door wide open and you will peg the highside guage when the condenser fan pulls air thru the door instead of thru the coil.
I'd check the condenser coil. it may look clean but it may be a 2 piece coil that you have to split to get clean in between the two halves. the unit is probably locking out on high head due to a dirty coil.

    Bookmark   August 2, 2007 at 1:07AM
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