We just recently bought another house, and I'm having some problems with the heat pump in heating mode.
We've got a Lennox HP25 411 1P heat pump as well as a 1 year old Carrier oil furnace which is acting as the air handler. We've also got a Lennox fuelmaster 21 as the fossil fuel kit(no outdoor thermostat is hooked up to it).
Anyway, the heat pump is noisy in the heating mode. In cooling mode, the heat pump is quiet; but in heating mode, it starts out rather quiet; but then gets louder and louder.
From the outside, I haven't really noticed an increase in noise, but you sure can hear it on the inside.
The heat pump also will stop heating, but the furnace fan and the condensor fan will keep running.
I have turned the thermostat off and left it off for a half hour or so and then turned it back on which caused the oil furnace to come on(the temperature in the house must have dropped enough to call for the emergency oil heat).
When the oil furnace satisfied the thermostat, the next time the thermostat called for heat, the heat pump started working again(although it still gets noisy).
The heat pump seems to stop heating when it's being asked to run a long time.
I've noticed also that it will eventually start heating again even if I don't turn the thermostat off. It just takes a real long time(like a half hour or more).
Anyway, what would cause a heat pump to run fine and quiet in cooling mode and then become noisy and sometimes quit heating in heating mode? Would a clogged up filter drier cause this or how about a defrost problem?
I didn't see a TXV.
I can live with the noise, but I don't really like the unit not heating except maybe when it's in defrost mode. Come to think of it, I don't think I've ever seen the thing enter defrost mode. Maybe it's too warm outside, or maybe not...
Thanks for any replies.
sounds normal for a lennox to me.
Is the indoor coil also a 1 year old Carrier coil?
Could the noise, or some element of it, be described as a low throbbing humm?
You could have a coil volume ratio problem. If the volume of the indoor coil is to low, compaired to the volume of the oudoor coil, the system is not able to reject as much heat from the indoor coil as is being absorbed by the outdoor coil. This causes the head pressure to shoot way up untill a safety switch shuts the heat pump off, high pressure releief opens and/or the compressor shuts off on thermal overload.
I have seen this many times when someone installed a newer high efficiency heat pump on an older indoor unit, but have also seen it on brand new equipment that was not properly matched.
There are other things that can produce similar symptoms, but most of the time I have seen it, it was due to to small of an indoor coil.
I'm not sure how old the coil is. I think the Heat pump is 11 years old though.
The noise is a low throbbing hum though. The noise will change in intensity(gets loud then quieter then loud again a while later). The pitch of the noise also changes.
If I hold my hand on the suction line, I can also feel vibration that gets worse when the sound is louder.
Right now, the heat pump is heating ok except for the come and go noise. Of course I don't know when it will stop heating again.
I called a dealer here that deals with Carrier and Lennox to come out and clean/replace the nozzle on the oil furnace and replace the filter(does a 2004 oil furnace need this?). They were too busy and referred me to another dealer who I left a message with but haven't heard from yet.
I also have a large hole in my ductwork after the air goes through the coil to the outlets that I was hoping to get repaired.
It seems someone has used cloth backed vinyl to connect two ducts together(why I don't know), and it's dryrotted.
I'll ask whoever I get out here for the oil furnace maintenance and duct problem about the heat pump problem.
I wonder if the oil furnace fan has more than one speed on it?
Thanks for the reply.
If it worked before with the older coil, but doesn't work now with the newer furnace, it could just be an airflow problem. Do you know if it has worked through a heating season with the new furnace?
The furnace blower needs to be moving ~1200 CFM when the heat pump is running in the heat mode or there will be high pressure problems with the heat pump.
The system could also be overcharged, wich can/will cause problems.
Very often the problem is due to a combination of factors. It wouldn't suprise me to find that the coil is a little small for the application, and that the system doesn't move quite enough air and that it has been overcharged.
Obviously nobody can tell exactly what the problem is over the internet, and it could be something totally different from the things I mentioned, so don't be to suspicious if the tech finds something other than the things I mentioned.
If it does turn out to be a problem with mismatched equipment, and you can't replace the equipment at this time, the tech may be able to get a "Mild weather kit" from Lennox to put on the outdoor unit.
The "mild weather kit" is a pressure switch that turns the outdoor fan off if the head pressure gets to high. Cutting the outdoor fan off in the heating mode reduces the amount of heat absorbed by the outdoor unit, wich results in lower head pressure, wich may reduce or eliminate the noise. It is just a bandaid and shouldn't be used as a permanent fix though.
[Edited by mark beiser on 10-25-2005 at 11:32 PM]
Mark, I don't know how the unit performed last year; but your replies make a ton of sense!
If you lived around here(Pulaski, VA) I'd call you for the service call if you wanted it.
Heck, the filter could be plugged causing high head pressure.
I just changed the filter and it didn't make a difference. The old filter wasn't that dirty either.
The unit works fine in cooling mode and is quiet too.
I wonder if I could cover up part of the outside coil similar to what truckers sometimes do to their radiators in the winter?
Hopefully I wont have to wait too long to get a HVAC company out here. The cold snap probably has created a lot of service calls.
Turn your thermostat to the emergency heat setting so you are heating with the furnace untill the problem is fixed.
I hate to burn that oil, but I guess I'll do it..