Temp Limit in Heat Pack Cycling - fixes?

[T-Comm]

Unit Info:
Heat Pump: TRANE XE1200 Heat Pump (4 yrs. old)

According to a professional serviceman who changed out my blower motor recently, the Temp Limit in the Heat Pack is cycling due to restrictive ducting (flexible ducting).

He set the blower motor to fast speed in an attempt to help alleviate the duct restriction.

As per his advice, I have eliminated all possible slack from the flexible ductwork in the attic. I cut out more than 8' of ductwork.

Temp Limit in the Heat Pack is still cycling. I'm assuming this will lead to further damage.

Are there any fixes available to me without calling for more professional service?
I am mechanically inclined and do my own work (provided i know the problem).

Any advice is appreciated.

Thanks,
T-Comm

[Jay11J]

What do you have for return(s)?

Air filter clean?

[T-Comm]

Air filter is clean, replaced monthly (or as needed).

Return is in main halway on backside of furnace unit. No obstructions.

Thanks.

[Ed Imeduc]

We want to know how many outlets on the unit do you have.ahow big are the pipe runs, how big is the return duct not the filter .It will all help.

ED ;)

[T-Comm]

here's the rundown:

Return Vent size: 18x22" (feeds directly into the unit's lower half)

# of Outlets (vents): 9

Bulkhead has 6 outlets:
- 3 with 10" ductwork split into 2 8" ducts to 2 seperate outlets ea.
- 3 with 8" duct to single outlet ea.
(this is from memory, but i'm pretty sure the ductwork was 10" and 8")

Longest Run of Duct: about 25'



lack of quality workmanship is abundant in this home. :wall:


(side note)
i did notice that the access panel covering the blower unit has a sheet of foil-backed fiberglass insulation on the inside that has separated from the panel and is being pulled towards the blower/internals when it's on. should i strip out or replace the torn insulation?

thanks for the help, this forum is a goldmine!

[scottg]

good call about the insulation on the door front.
Take a peice of metal strap and cut it to fit the width of the door and screw it to it to keep the insulation against the door.

You should have 400 cubic feet of air per min. going thru the unit per ton. With a minimum of 350 c.f.m. per ton.
Example 2 ton should have 800 c.f.m.
to test see how many kw heat you have installed in the air handler then operate heat pump in the emergency heat mode and get return and supply air temps then

Kw times 3.414 divided by 1.08 times the difference between supply and return temps.
Or kw X 3.414
1.08 X (return - supply temps)

[Jay11J]

The insualtion will cut down on the air flow, and cause it to go into high limit.. make the repair, and that should solve the problem.

[T-Comm]

thanks a million.

i'll replace and strap the insulation sheet back onto the access panel and see if that helps.

hopefully this saves me a service call.


i'll also sit down and do the volume calculations this weekend.


thanks again for all the help, this forum is wonderful!

(i'm off to see where i can be of help elsewhere in the forum; i'm no stranger to moderating) :)

[T-Comm]

i just had another thought.

i remember that when the serviceman replaced my blower motor, the fan surrounding the motor didn't exactly seem to be rotating evenly (wobbly, but not rubbing anything).

i know from experience that this isn't an ideal situation and could cause undue stress on the motor eventually.

would this slight offset cause the motor to overheat? (this motor is 1 month old)

running just the fan (no heat), what should the optimal temp. for the blower motor be?

thanks.

[scottg]

Blower motors should not be over 100 degrees and closer to 90 degrees

[T-Comm]

thanks again.

[Grady]

With the insulation issue, it might not be a bad idea to check the coil to make sure no insulation is plugging it. Another possibility is the flex duct is coming apart internally. I have seen the interior liner of flex become separated & cause a duct blockage. Sometimes it can be tough to find. Better yet, get rid of the flex except for a short (<5') connector to the register boots. Use metal duct wrapped in foil faced fiberglass.