Trane Heat Pump: Permanent 24v to Reversing Solenoid?

[Steve Cutchen]

This is good to hear... I did not know about the defrost cycle being this often while in heat mode. I feel better about the RV cycling with the A/C demand and being able to handle it.

[Steve Cutchen]

This is a good idea, but costly compared to wiring 24V to the solenoid. Still I appreciate the suggestion because if the valve ever does fail I could simply have sections of tubing installed rather than having a new RV put in.

This is a big deal, because installing an RV in the field is a PITA, what with nylon parts in the valve so close to where the heating is taking place. I've read that some techs will not even try to do it in the field because of the difficulty in getting it done without screwing up the valve internals.

[RP]

That's a Carrier stat. BTW, I'm trying to figure out exactly what your question is, and best I can tell you're wanting step by step instructions on how to hard wire the RV in. "Have your service tech" put O under R instead of Y, at the stat. There are no warranty issues because the system is already out of warranty. Do not attempt to rewire the old stat or any other HP stat back in yourself, as a dual fuel system requires extra controls that may or may not be installed. OTOH, you might be interested in knowing that RV noise is normal, excessive RV noise is not. You may have an indoor airflow restriction or an overcharge causing excessive head pressure in HP mode. I don't know your location, but in the Mid-South a HP is currently cheaper to run than a natural gas unit. Some people find the normal RV noise to be irritating, especially if the unit is poorly located. If this is the case, then you might keep in mind that Carrier offers a unit with a Quiet-Shift (TM) defrost board, especially for customers like you.

Richard Perry

[stretch]

I'm a Trane dealer. Wiring the 24 volts to the reversing valve solenoid will NOT void the warranty, especially if you do it at the thermostat wiring connections on the outdoor unit. Just wire orange to red at that point. Yellow will continue to work the compressor contactor. Blue (Common) should always be connected. White can be disconnected in this application. Looks like he installed a new high efficiency gas furnace and indoor coil in place of the air handler. Probably didn't like the HP discharge temperature in heat mode. He wanted that warm feeling that gas gives him. Very understandable. He already had the heat pump outdoor unit & used it over. Nothing wrong with that. His dealer did a reasonable thing to use the heat pump outdoor unit over if it is not too old. The noise is the real problem here, unlikely that the reversing valve will stick. This is just a simple control issue. He does not need to throw lots of money at it buying a new condensing unit. On the other hand, if the outdoor unit is

15 years old, he should have been sold a new condensor by the dude who sold him the new furnace. But don't complicate things, have the furnace installer come back and rewire the controls. Remember, low sound levels are part of comfort.

PS. If you turn the HP breaker off, turn it on 24 hours before you start cooling to energize the crankcase heater so you will protect the compressor.

Stretch

[stretch]

If the reversing valve fails after 10 years, it is more economical usually to replace the HP. In your case with a straight A/C condensor for just cooling. Make sure your new condensor matches the indoor coil, or replace it at the same time to match.

Stretch

[Steve Cutchen]

Thanks very much for the post.

The gas furnace was installed at the time the house was built. There was a kickback from the electric company if a HP was installed instead of a traditional AC, making it cheaper for the builder to install a HP thn to install a traditional unit. I'm not sure why they still installed a high efficiency gas furnace, unless there was a concern by the builder about the perceived comfort issues you mention below. I think they did not want to try to sell houses with electric emergency heat, and if they were doing a furnace anyway... well do a decent one.

This is Houston, and gas furnaces are an extremely high percentage of heat units, especially in moderate to expensive homes. Some entry homes are all electric, and these have been going HP for a while. But it is pretty rare.

[Noon-Air]

So as I said before if you put the correct stat on the system, you won't have that problem anymore.

[Jake]

Thanks for the correction and the explanation... I kinda 'belched' out that answer only because I didn't like to see monkeying with controls is all....

I stand corrected on the issue.

BTW, the 'belch' wasn't a bullshit one, though. We see pumpdown modes on big equipment all the time before they do switchovers (like in duplexed systems). I was just curious why you wouldn't have one on a resi system? I'd think (oh no, here I go thinking again) that lessening the system shock would be good for all the components and might even make them less expensive.

Or maybe I'm wrong, AGAIN (Damn, I hate that (-; ).

Jake

[pjm]

The 'shock' of the pressure change really mainly hits only the coils, IE, some copper pipe, which doesn't really care. Not too much of it hits the compressor, in volume ( and thus, 'work' ) terms.

The noise is just noise.

[Jake]

Call me an idiot if you like... do I still not get this?

The RV is switching the suction and discharge around? So you have high pressure at the suction and low pressure at the discharge (for a little while, anyhow).

Doesn't the compressor have to 'make up' the P in the switched discharge line to be efficient? And I'd worry about the mechanicals of low pressure carrying lubricant successfully (it would appear the compressor is operating in a 'vacuum')? Why wouldn't a modern compressor, like a scroll, want to turn backwards when this happens? That should mean more 'work' to keep her running.

Dumb questions, probably. I'm still just curious... I deal with GB systems all the time that work harder than this stuff.

Jake

[pjm]

Idiot :-)

Yep. The outdoor coil ( used to be discharge condensor ) is now the evap, and the indoor coil ( used to be evap ) is now the condensor. But, the high pressure seen at the compressor suction line is only momentary as the indoor coil is pulled down to suction pressure ( while the outdoor coil goes to discharge pressure ), NOT for the entire defrost cycle !

Who P'd in the discharge line ???? Damn, I hate when that happens ..... not as much as the guy who tried P'ing in the discharge line .....

Yes and no, in that order. Yes, carrying the oil is always an issue in ANY suction side, as the oil is a liquid ( mist ) entrained in a vapor at that point, and dependent on velocity to carry it around and back.

No, the compressor does not go to a vacumn. A different expansion device takes over from the first one, ( which is now out of the circuit, either by check valves around it, or other means ). The ( other ) expansion device is now metering liquid into the outdoor coil , which is now the evap ( I'm talking about heat mode here ). In defrost, they change back to AC mode, and the discharge again goes to the outdoor coil, this time to assure there's no ice on it.

The power of the compressor greatly overpowers the power of the refrigerant pressures. If it didn't, you got problems :-)

[Vicki Szaszvari]

Twenty years ago you could. Anyone else remember that?