What are you looking for? The XL18i system is a two stage system, the XL15i system is single stage. The selection of the size of the air handler is very important for best performance/efficiency numbers. 4655313 Active Systems XL15I WEATHERTRON TRANE 4TWX5036B1 *AM7A0C36H31 1225 37600 12.50 15.00 34600 9.25 21800 1 HRCU-A-CB Yes 311 751 Yes TAM7 36 size for the 3 ton XL15i system. 7117217 Active Systems TRANE XL18I TRANE 4TWX8036C1 *AM7A0C42H31 1185 945 37000 13.00 18.00 31400 9.50 20200 1 HRCU-A-CB 255 627 Yes TAM7 42 size for the 3 ton XL18i system. If this is not a budget decision, then get the XL18i system as I listed with 10 KW heat strip. Pay attention to the air handler model/size. If you are able to interpret the AhRI numbers, you can readily see there are some marginal savings with the XL18i system on cooling and good savings on heating with the higher HSPF efficiency. You are getting some very good pricing. I am done here. IMO Good Luck This post was edited by tigerdunes on Tue, May 20, 14 at 6:37

echo your 3rd party contact is telling you correct. while the 3F40B VS air handler is an AHRI approved match, that is not the best choice. 1384601 Active Systems XL15I WEATHERTRON TRANE 4TWX5042A1 4TEE3F40B1 43000 11.90 14.25 43000 8.60 28200 here is a list of better air handler choices. 4385470 Active Systems XL15I WEATHERTRON TRANE 4TWX5042A1 *AM7A0C48H41 44000 12.50 15.25 43000 9.20 27400 1382172 Active Systems XL15I WEATHERTRON TRANE 4TWX5042A1 4TEE3F65B1 42500 12.50 15.00 42000 9.00 27200 I like either of these two choices over the 3F07A because of the higher HSPF heating efficiency which would be a plus for a Md location. IMO

I am in agreement with everyone, the unit is old but as stated, was purchased by TRANE. However, the relays and other supporting parts are readily available. If I'm correct, I think Tigerdunes was pointing in the right direction. If you are not familiar with heating with heat pumps, then the air coming from the vents while in the heat pump mode alone, would feel cool to you. One thing you mentioned was that while it was in the heat pump mode, you did not measure voltage to the element. That would be normal. When the unit calls for AUX or Emerg. heat, then you would get a voltage to the heaters. Here's what I think is happening....the reversing valve is stuck...it was common on the older units. The unit stays in the cooling mode and when the first bank of heaters comes on, the cool air overcomes the full effect of the heater. Check the air coming from the outside unit. If it is warm and that will confirm the possibility of a stuck reversing valve. As mentioned also by Tigerdunes, replacing a reversing valve is expensive and given the age of your unit, whole replacement of the unit would be a better choice. Now a professional should be called however, I'll give you one thing you can try, if indeed it is still in the A/C mode. You can force the valve to slide into the heat mode by doing this.....disconnect the blower at the condenser. Turn the unit on in the heat pump mode and let it run....Given your temperatures, the condenser will slowly build pressure on one side of the valve as the pressure drops on the other side. You'll know you are getting close when you hear the compressor staring to load up. You'll suddenly hear a whoosh and the reversing valve has now reversed. Let it run for about a minute to make sure it has fully reversed. Shut the unit downand hook the fan back up. When the unit goes into the defrost mode, the valve may work and the unit defrosts but may not switch back to heat mode (sometimes they do, sometimes they don't.) If that's the case, you have to do it all over. This suggestion is just to get you some heat until you get someone out.

The crankcase heater seems to be standard on this heat pump (see page 2). http://blue-phx.com/pdf/Trane%20XR14%20Performance.pdf I would guess the other option he wants you to buy is a hard start kit, which is a capacitor (see page 5 of the link above). That is only needed when the supplied line voltage is marginal from the power company, or sometimes when there is a lot of refrigerant to get moving at startup when you have a long lineset going to the second floor. Occasionally, you can extend the life of a very old compressor with the kit. In other words, the capacitor is used when the system does not work without it. It is not a preventive maintenance item that would make your system last longer.