kok328

I just love it when this help forum pays off. In this case it paid off to the tune of $3500.

paponertelo

Guess what? My same Trane unit would not start in AC mode last night. It worked perfectly all through the winter in furnace mode. I had no response when I switched to AC so I went and checked the control unit and the LED did not light up. The transformer is working because I can hear it hum. Earlier today, I remembered that the new control unit (White Rodgers 50A55 843) has a fuse and when I checked, it was burnt. I got a new fuse and when I turned on the power, the control unit LED started working and made a sound like a relay. Went to the T-stat and turned on the fan/blower and it kicked in and worked. Then, I switched to auto and changed the mode from off to cool, nothing happened. Checked and found the fuse burnt once again. I replaced fuse with a new one and control unit lit up again. Did the on for the blower and it runs. I have not tried to call for cool and visually inspected and felt the wires going to the T-stat and to the condenser/compressor unit; all seems to be okay.

I'm trying to figure out what to test and how. It seems the problem is when the condenser/compressor unit has to kick in. I'm thinking of going to the unit and checking the connections at the contactor and the wire outside. Then, if it checks out, test the wires to the T-stat. After that, ???

Any recommendations, hints, testing sequence, past experiences that any one can offer/relate that may help? Thank you and have a great memorial day.

PS: We experienced severe T-storms about a week ago, but he unit was not running at the time although it was still in heat mode.

hvactechfw

Most likely orange is shorted to ground if heating mode works on your HP. Or the reversing valve coil is bad. Switch with extra wire if you have any in the loom

paponertelo

Hi hvactechfw and thanks for your insight. I checked the orange wire with my ohm meter and the wire is fine with no grounding to cabinet. However, the Valve switch it connects to reads ground no matter how I test it. It's a round vacuum activated/reading valve (photo attached) with 3 electrical connections, 1 orange and 2 yellow. Any way you check it, between wire connections, chassis, or ground, it has continuity. The terminal the orange wire is attached to looks burnt/discolored (see attached photo). Is this the reverse valve you referred to earlier? If it is, I'll replace it with a new one. Thanks again.

PS: is there any way I can test that this valve/switch is bad and causing the fuse burning problem without swapping the valve with a new one. If this is too dangerous or can hurt other components, I won't try it.

hvactechfw

DO you have a Heat pump? Orange would be at the thermostat and not in the furnace. That is a picture of a Pressure switch in the furnace.

paponertelo

I have a Trane Gas Furnace and AC unit. The wires to the T-stat are Green, white, Yellow and Red. There is a fifth Blue wire that is not used. At the controler board there are an extra couple of wires that I believe go out to the condenser/compressor unit. Here's a photo of both.

paponertelo

I have attached part of the documentation that came with the unit. The furnace unit is a TUD080C936A. I could not attach the whole .pdf file because of attachment size restrictions on this site. I could email if you want/need all documentation. Maybe this will help.

hvactechfw

ok, You need to check the wiring from the control board inside to the outdoor unit. red is hooked to Y on control board and white is hooked to C. Follow those wires ( should run with the a/c copper lines to the outdoor unit) and check for missing insulation or grounded out wires. IF nothing is found their or inside the outdoor unit then it is most likely the coil of the contactor in the outdoor unit is bad, check the resistance of the contactor coil.

paponertelo

Checked the wire that runs to the outdoor unit and the insulation worn out close to the unit. Any considerations in terms of what wire to use to replace it; outdoor rated, solid versus stranded, any voltage or resistance requirements, where can I get it (Home Depot, Radio shack)? Thanks.

hvactechfw

18/2 solid wire...should be at the HD