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Discussion Starter #1
Basics....unit is a Trane TWRO24C100A0 compressor and a TWHO24B140A1 air handler....been working for quite a while with no problems, but 2 years had a cap go...replaced cap and relay in the compressor, no problem until last winter....it quit while I was out of town working. Wife called local HVAC folks...they came out and put in a new Thermo (H-Well "PRO-3000) thinking that the old one had died (But apparently did no trouble-shooting as my wife wanted a programmable thermo anyway.) The tech wired the heat strips to be activated whenever the "Emerg. heat" setting was activated...got us thru winter but ouch on electric bill! This spring, switched over to air cond....no compressor activation! Tech has been out twice, said "Wiring bad between thermo and air handler". Huh?? I took thermo off wall, went under house and direct wired it to the A/H. Unit activates fan, no problem, but NO activation of compressor.

2nd visit tech says, "Fan control Board is bad...." So I got a new RLY02807 and installed. A/H fan works fine, but still won't activate the compressor. I did note that the LED on the defrost board in the compressor was not blinking as normal...tech says, "NO Big deal". I confirmed 24 VAC and proper AC to compressor (Push in relay and compressor runs...just RELAY not being activated).

WIfe is in NO MOOD to hear my tales of troubleshooting....she's in the "REPLACE THE D*^^ thing" MOOD. IF I had the $$, I'd do it just to keep the peace...but in the current economic climate, I"d REALLY like to get this thing running and get at least a few more years out of it....

Any hints, comments, or even a "HEY STUPID, REPLACE THE DA^^ thing?" Turning into a real head-scratcher for me....I'd really just like to know what the heck is wrong with it. More for my own knowledge and to tell the tech "Please look in this area."

A thousand thanks in advance!!!

Derswede
 

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So you took a meter and measured 24 volts between the low voltage leads on the contactor and it didn't pull in? If that's correct then replace the contactor.
 

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Discussion Starter #3 (Edited)
So you took a meter and measured 24 volts between the low voltage leads on the contactor and it didn't pull in? If that's correct then replace the contactor.
Darn, forgot to include that point...have 24vac raw feed to the outside unit (compressor). Tech was saying, "NO 24V to outside unit" but it IS there...swapped defrost control boards with the upstairs compressor....board is good, runs fine in 2nd unit, but no blinking LED on board in first ("downstairs") unit....?? NO coil voltage to the unit's contactor....

Thanks for your comment...forgot to add that part about tech saying no 24V to outside unit...measured and checked twice. What controls the main contactor in the compressor....in other words, what is the activation sequence to activate the compressor motor?

Many thanks!
Derswede
 

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Should have 24v between r&c,Y&c and o&c at the heat pump terminal strip with a call for cool. If the pressure switches are closed then the board will send 24v to the contactor after a 5 minute delay. The blinking light is powered from r. Knowing which terminals you have 24v at would help a bunch.
 

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Discussion Starter #5
Should have 24v between r&c,Y&c and o&c at the heat pump terminal strip with a call for cool. If the pressure switches are closed then the board will send 24v to the contactor after a 5 minute delay. The blinking light is powered from r. Knowing which terminals you have 24v at would help a bunch.

Marty,I bow deeply in your direction. That info should let me check thing and see if I or the Tech can ID the problem...MANY THANKS!
Derswede
 

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Discussion Starter #6
Hmmm...OK, I'm getting 24 VAC between the BL & YL wires into the defrost control board. I swapped the board with the working upstairs unit, so it is good. Also bypassed the load control setup to verify that it is not faulty.

Next step is to bypass the wiring to the compressor..Got the cable ready, but too many t-storms around this pm to let me finish. Still scratching my head,esp in that I STILL get no blinking LED on the defrost control board. I must be missing something (Other than my brain....:laughing:)).

Derswede
 

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But do you get 24 volts when measuring across R and BL?
 

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also there could be a sensor or pressure switch that is keeping the board from sending signal to contactor to pull in
 
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