Heat Pumps and Electric Heating - Trane Xe1000 Auxilary Heat always on

System is comprised of Xe1000 (3 ton) and Trane 1.5 ton A/h. Previous owner of the house I suspect hodge podged it together. It has run fine for the past summer in cooling, however, last winter nearly broke me. The "Auxilary" heat light on our white rodgers programmable t-stat pops on about 3-5 minutes into heat mode. I put the t-stat in about a year and a half ago when we moved here.
I have checked the wiring, and the only thing I am not 100% about is the O/B connection, apparently, the t-stat does not energize the o/b when in heat (for switching the reversing valve,) just in cooling. This seems to work well as cooling worked great over the summer.
When I switch on the heat initially, like in the evening when it has been off or set really low temp and it is warm outside, the compressor initially will kick on and the (normally) suction side line gets HOT and the h/p line gets warm, with what I believe is residual heat coming back from the evap (operating as a condensor.) I checked with a multimeter on the output (yellow) on the t-stat and there is indeed 25V as a signal to run the compressor. However, after a little bit, the compressor will not actually run, even though there is a 25V signal telling it to do so.
I looked at the schematic and see there are to thermistors, one for "coil bottom sensor" and the other for "outside temperature." Is it possible one of these is sending the control board in the Xe1000 a bad signal? Is it possible the mismatch between the two unit sizes affects the heating cycle to the point the coil gets too hot and tells it to shut the compressor down? I did have to change the control board last fall, shortly after we purchased the house, and Trane had changed the style of the board a little. Any suggestions are greatly appreciated.
I am NOT a HVAC tech, but very familiar with the theory behind the cycle and very confortable with eelctrical t/sing. Any guidance is welcomed. Thanks!

The indoor coil is your condenser coil for the heat mode.
An undersized evaporator coil will cause excessive head pressure and could be causing the compressor to drop out on hi pressure.

Verify that your air filter and the evaporator coil are clean.

I recommend a new heatpump system.

Thank you for the reply. I am a blooming moron as I went to check this thread, could not find it (looking in the wrong place,) and rewrote it and reposted it. If a moderator sees this, I put it under A/C for soem crazy reason. I apologize. A little frustrated at the job.
Thanks for the reply. I will check this ont he schematic. I will also put my guages on this as I should see this is high pressure going into the evap in the a/h (yes - acting as a condensor - rejecting heat.) Too last night to do this.
Absolutely no funding available for a new system, not even a low-budget Goodman. It is either fix this, and feed the kids, or feed the kids and be uncomfortably cold. Not much of an option, unless selling an organ qualifies.
I will check pressures and the schematic. Thanks for the tip.
Oh, and yes, the evap is very clean - did that last spring. Filter changed every month due to child with severe asthma.

I am NOT a HVAC tech, but very familiar with the theory behind the cycle and very confortable with eelctrical t/sing. Any guidance is welcomed. Thanks!

Go down to your local HVAC supply house and purchase a Honeywell Pro 5000 heat pump tstat and install it. BE SURE to check your tstat wiring, disconnect at both ends and check for shorts between each seperate wire. It is common for mysterious problems to develop with bad tstat wiring, that white rodgers tstat is junk you need to purchase a quality tstat and have good wiring then you will be so happy.

Thank you Former Member, will do tomorrow. So I have had a chance to fiddle with it a little more. Pressure on the high side at the line set will climb to about 400 psig or so, then after something is opening up, drop down to 325 and hold steady, at the same time, the suciton side (at the inlet to the CMP) will pull to about 70 psig. This is all on about a 55 d-F evening. The outside coils get cold, the lineset going in gets nice and hot. This goes on for about 10 minutes or so, holding pressures (this is indeed higher than I see on the high-side during the summer, seems like that ran at about 82 d-F at 265 or so) then the compressor shuts off, about the same time, the Aux light comes on in the t-stat. Today, I tried it again and this time it continued to run, no aux? So there is an overload in the cmp, I presume, this is for temp? Where is the pressure switch referred to? How does the t-stat know to kick on the aux light, I though it (the t-stat) controlled this as that is where the relay apears to be? This is the controls part that just does not seem clear, perhaps it will go away with the Honeywell? Thanks again, I iwll go get this tomorrow.

Installed the Honeywell t-stat, and in doing so found a couple interesting tidbits.
1. When I replaced the control board in the compressing/condensing unit outside last year, the "new" version sold to me by the trane dealer did not have a t1 connector, this left the brown wire, that is supposed to go to the outside temp sensor (thermistor?) and hence it was dangling. I read in the A/r manual, if no OTS then the three white wires are supposed to be connected, which I proceded to do, since the OTS was supposed to go to the brown wire, which no longer exists.
2. I read this eveing about a Accutron Flow Control valve, that apparently is "tunable" for flow. Mine currently in the 1.5 ton unit is a "49" and the one my heat pump unit specifies is a 71. Can I simply change this out to help drop my pressures (increase my flow) for the larger heat pump unit?

Although the ambient temp outside is warm (mid 60's) again, the unit ran without kicking on the aux heat. Not certain how it will perform when it gets cold again though.
Any other advice or ridicule is welcomed.
Thanks.
Jeff

there is an AHRI site for matching coils to condensors I do not have the address available right now but you could not sign in anyway. The orfice may be incorrect but requires service to the sealed refrigerant system to change it out so it is outside the ability of the DIYer. Might want to have a service guy drop by and check the AHRI match numbers and orfice size for you, they should have tagged the line where it is installed so you can see what is there. Could simply be a case of an overcharge and a good tech could fix that for you for a reasonable amount of cash. If you would like to post the coil number and heat pump condensor info and actual installed orfice size someone might be kind enough to check it for you.

You do have a mismatch in outside to inside. When I had an old GE unit replaced they reccomended instead of a 36000 BTU air handler to use a 42000 to get higher effiency. This was in 2000. It worked good but in the last several years I noticed a drop in vent temp and aux heaters coming on more often. The top temp in the air handler was about 85 and slowly got down to 83 with a return of about 72 degrees. I called a friend (yea) and he said it was low on freon. All it did was no heat at all and the compressor was laboring. Could not get him back and called a local Trane dealer as the one that had installed it closed. After troubleshooting it was found that the built in filter dryer was stopped up. It was straight piped and a bidirectional one installed on the outside which should have been done to begin with. My old unit did not have one as sealed precharged lines was used but on this unit they used tubing off a roll and no plugs on the ends to keep dirt out. Anyway my temp went up drastically. That day it was 15 degrees and the top of the handler was in the low 90's. Right now tonight with it in the 50's the temp is near 100 degrees. My wife has a respiratory problem and we run the temp at about 75 degrees. It reallyhelped our electric bill but with steady increases it gets hard to tell and have to compare the kw's used. Hope this helps.