HVAC guy needed, may need some creativity

[RatLabGuy]

Looking for input, and likely an HVAC fellow who's interested in a small project.

Our house is 42 y/o, originally had oil heat. At some point it had a heat pump/ac put in. Still has the oil, it's set up so that the oil is a backup unit, "secondary heat". 2 ways it will kick in to oil - it has a thermostat w/ a dial, so you can set a minimum temp, below that, it kills the heat pump and the oil runs by default. Also, if the heat pump is shut down to defrost or something, it switches to oil.
In theory, this is a good system, b/c oil is more efficient when it's really cold.
However, w/ the cost of oil what it is now, it's really not worth it 98% of the time.
I'm having an issue w/ the system. For some reason, the heat pump will run for *maybe* 10 minutes, then shut off, like it needs to defrost - although we're talking about the current 60 deg weather, and only raising the air temp like 1 deg first. Any ideas on what would cause this? After just a few minutes, it comes back on to keep going.
The real problem comes in when it shuts off - the system sees that it isn't running, and switches to oil. It then stays on oil until the t-stat is "happy" and kills everything - even if the heat pump is ready to go again. As you know, once on, heatied, and flowing, the oil furnace keeps pumping air out until it's cooled off, even if this means an overshoot of the target temp. Point being, it can end up running for several minutes and using oil when not necessary.

So i'm looking for 2 solutions.
1 - what could cause the pump to need to shut down so often?
2 - More globally, I'd rather re-wire the system so that it is only a manual switch between oil and heat. Oil costs so much that it would take a 25%+ increase in my total electric bill to make it worthwhile to ever use. Only would want it when really cold and the heat pump can't keep up (which is very rare around here).

I have no idea what would be involved in the rewiring, thinking that'll need to be left to somebody that knows what they're doing...

 

[Ron]

First thoughts on cycling on-off
are
1) Low on freon(could cause freezwe up)
2) could have a weak contact inside thats onits last leg

As to the wiring, if you want an easy fix, find the wire at theheater that kicks it on and wire it in to a regular old 20A switch. You would then have a handy disconnect. T-Stat still does its deal, but only effective when you sitch it on

 

[shawn]

I can't help you with the heat pump issue... but I'd be willing to bet that you won't be able to get away with not using the oil heat. We've got a similar setup, using a gas furnace as the backup to a heat pump. The thing is, when the heat pump is "heating" the house, it's kinda like being an air conditioner in reverse. The coil outside can ice up even when ambient temps are in the 50s, depending on the humidity and such. When it goes to defrost, it switches back to A/C mode, and also fires up the furnace to keep from blowing cold air into the house.

I know our furnace kicked on for the first time several weeks ago... in the late afternoon. It couldn't have been but 50F or 60F outside, but the heat pump switched over to defrost mode. The only reason I noticed was because there was a summer's worth of dust buildup in the furnace that needed to cook off.

You could look at getting an electric heater to go with your heat pump... then you'd have the option of letting the electric one run, or switching over to oil.

Hope that helps.

 

[RatLabGuy]

First thoughts on cycling on-off
are
1) Low on freon(could cause freezwe up)

This is entirely possible. This summer it seemed liek it oculd barely keep up. We've been here 4.5 years and I don't think it's ever been checked. This will be the first step for sure.

 

[Yay!Gurrr]

I'd simply look at adding the elec. heat coils. Most systems have it as an option.. Probably be easier all around and possibly cheeper depending price of oil..

Granted ill say my heat coils are on alot when its really cold but elec is still cheeper.

As an aside im seriouly looking at adding some addtional insulation in the attic.

 

[RatLabGuy]

So - any licensed HVAC guys interested in a quick job at my place? Or else, anybody have a recommendation for somebody in the winston/Lewisville area?

 

[RatLabGuy]

Update.
Last night, forseeing cold weather, I decided to try something.
Got out the manual/ install info for the nifty touch-screen Rite-Temp t-stat I installed last year.
After comparing the wiring connections for "heat pump w/ aux" vs "heat pump w/o aux", realized only 1 wire difference. So I disconnected the wire feeding th aux source (oil furnace), so the nifty smarty digi stat wouldn't know it was there.
Low and behold, it works fine now. Pump runs until temp hits the target. Interestingly, though, the indcstor will switch to saying "heat 2" like it did when switching to oil... but it just keep running...

So anyhow, I'm not real sure what the difference is now. Still want to get the freon checked just so I know.
ButI'm thinking I can put a switch on this line that I removed from the stat, use that as my manual switch between oil and no aux unit. Thoughts?