Maryland WF Series 7 units increase to second stage before turning off

We just had two WF S7 3-ton units installed with our new geo system and live in Maryland outside of DC. The contractor did a Manual J to size the units for our 5-level split roughly 5k sf house. Basement unit has 2 zones approximately equal square footage. The garage unit has 3 zones of varying size. Since installation, the basement unit primarily (and the garage unit to a lesser degree) will ramp up to second stage for the last 20 seconds of most cooling cycles prior to shutting off. Always the same 20 second time duration, only occurs at the end of a cycle. Otherwise during cooling cycles we do not hear the units running but are often distracted by the significant increase sound in air movement and, depending on where we are in the house, sound from the units themselves. Overall, the units do a fine job cooling the house and humidity is well controlled. The contractor made some adjustments initially that seemed to make the 20 second ramp up stop occurring, during which time the unit would go from its normally near silent operation to off at the end of a cycle. After 2 days the ramp ups resumed. The contractor is coming back out to look again, but made a comment about how it may be the result of one zone being on and the other zone off or the unit cycling oil as part of its standard maintenance, but they will look more closely when they are out next week for our final walk through.

Is this 20 second ramp up in the unit prior to ending a cycle normal? Do the possible causes mentioned by the contractor sound plausible or is something else more likely? Thanks for any feedback.

 

I also just had a Series 7 installed. Do you mean the compressor ramps up to a higher stage, or the blower itself ramps up??
I cant say I noticed my compressor ramping up, but I have heard the blower ramp up.

 

Interesting. Your blower ramps up the same way, last 20 seconds of the cycle? How frequently?

We hear air blowing faster, so I assume that means at least the blower. But it also sounds like the unit is louder. I'm not sure how to distinguish if that is just the blower or blower + compressor?

 

If you have the symphony, you could log into it, and then watch it when you hear the cycle start up, and monitor the compressor and blower stage when it ramps up.
Keep in mind that the Series 7 doesn't have a high and low stage. I think the compressor can be 0-12 stage and the fan is 1-10(I think)

 

Sorry. To answer your question, I believe it (the blower) ramps up every time the unit cycles. I have yet to have a heat cycle, but I can only assume it will do the same thing then.

 

Yes, that does sound right. I'm still curious to know why the unit ramps up. The conventional AC/AH systems that the S7 replaced did not do this and I'm not real excited about hearing the system like that every time it cycles. Would like to know if there is any adjustment to settings that might prevent that, unless there is some very compelling reason it needs to occur. Would be a little bummed to hear "that's just what geo package units do!" as some explanation for a unique oddity about how they work that necessitates this ramp up :-(

 

I would rather hear that than my old AC unit from 1986!
You could email Waterfurnace. They are very responsive.

Out of curiosity, did you get the symphony with yours?

 

Unit usually goes into stage 6 at the beginning of the cycle and every half hour for about 20 seconds to ensure that enough oil is circulated through the compressor. I can only assume that the fan goes up to higher stage at the end to remove residual heat or coolness

 

Since it finally warmed up today, my unit kicked on.

I did notice at the end of the cycle, the compressor speed was at 9 and ramped down to zero as the blower was at 8 (at least when I finally heard it) and ramped down to zero as well.
Not really sure the reason. It didn't seem to last very long.

I am curious what the unit considers stage 1 vs stage 2 for cooling and for heat.
If I remember correctly, the installer told me that for cooling stage 1 is 20% unit capacity 2 is 30% etc,... 8 is 100% then 9 and 10 are the superboost mode which is 110% and 120%.
I don't know what defines stage 1 and 2. No clue on what the stages for heat are either

 

Normally the Series 7 should run hours and hours at a time even with low loads, ramping up and down to match zone calls. I find it hard to believe yours was running at top normal cooling speed and decided to shut off, unless it encountered a soft fault or all the tstat setpoints were changed or it went into a programmed setback.

The fan does continue to run at the same speed 20 seconds after a normal compressor cycle. Changing air flow sounds might be associated with dampers changing position during this period.

I assume you have the IntelliZone 2 zoning system.
Do you have 2 or 3 wire dampers? Is the MasterStat configured as such?
Are any of the zones set to Economy?

 

I do not have the intillizone. I have a single series 7 with the AWL (Aurora Web Link)
My unit doesn't run all the time, keeps the house at a constant 73 degs (tstat setpoint) I believe it was running that high of compressor speeds to bring the humidity down in the house. The house had been open for a couple days when it was nice outside.

 

Neokane
Sorry. Joshua said he had a zoned system but you may have provided the clue to what is happening.

Dehumidification – Active


Active dehumidification will only activate during cooling operation and is based upon the humidity setpoint of the thermostat being at least 5% below the actual relative humidity and being within the temperature parameters described here. The green status LED will flash code 2 when active. The unit can operate a maximum of 2°F below the cooling setpoint. The compressor will ramp up and airflow will begin at a low level. Airflow is then reduced periodically until air coil temperature setpoint is reached. If coil temperature continues to drop, the airflow is increased until air coil setpoint is maintained. After 20 minutes of operation in the Active Dehumidification mode, normal cooling operation will resume for 5 minutes. This cycle continues until the dehumidification setpoint is reached, room temperature is more than 2°F below cooling setpoint, or more than 1°F above cooling setpoint (normal cooling takes over). In IntelliZone2 systems, the main zone will remain open during active dehumidification.

Perhaps the fan runs at "normal" speed based on last compressor speed for 20 seconds after the compressor shuts off after the Active Dehumidification call is cancelled.

 

There are reasons I like analog I/O.