Temperature in the supply plenum rises above what the manual says is the max...pretty quickly. I've been trying to figure this one for many months and it's a mystery. Any insight much appreciated.
Communicating modulating Amana AMVM960603BX furnace with three zones controlled by an EWC Ultra-Zone board. One communicating 'stat, two regular 'stats. The dampers all work. Manometer says total static pressure is less than 0.5 no matter how many zones are open (summing measurements at fan intake plenum after filter, before AC coil with the coil panel open and a hole drilled thru the cover plate, and after the coil). For example, with all zones open and fan speed about 1200 cfm it's about .15 before the fan, about .22 before the coil, and about .12 in the supply plenum. And my anemometer says about 1200 cfm airflow thru the supply plenum. Looks like the air is moving as designed.
The manual for the furnace say an OK temperature rise is 20 to 50 degrees. But no matter how I set the zone board to stage the furnace, the supply plenum temperature gets above 120 degrees within five minutes of heat-on call (return air is about 70 degrees). It looks to me like the core problem is the fan speed is set according to the gas flow: For example, if gas is 100% of maximum then the fan runs at 100% of the speed chosen on the dip switches; 50% gas means 50% fan, and so forth. That is, I can't tell it to run the fan faster than the gas percentage.
What works OK is to set the dip switches so the furnace fan is at max for any given gas percentage, and set the target target temperature on the zone board at 120 degrees and then have the zone board overtemperature cutoff at about 130 degrees. The zone board calls for max heat at startup until the supply plenum gets near 120, which means the fan runs fast. Then the fan and the gas slow down, but there's not enough air to keep it below 130%, so the zone board cuts off the furnace while keeping the fan running, waits three minutes, and starts the cycle over again.
So, I'm letting the supply plenum temperature go 10 degrees above what it says in the manual, but on a cold night, say 10 degrees outside, the thing can barely keep up because the gas is off almost as much as it's on.
And it bugs me to be using a safety to operate the system.
Anyone know of a way to jigger the furnace control board to give me a way to set the fan speed separate from the gas flow?
Sorry for the long post. Thanks!
The problem:
Communicating modulating Amana AMVM960603BX furnace with three zones controlled by an EWC Ultra-Zone board. One communicating 'stat, two regular 'stats. The dampers all work. Manometer says total static pressure is less than 0.5 no matter how many zones are open (summing measurements at fan intake plenum after filter, before AC coil with the coil panel open and a hole drilled thru the cover plate, and after the coil). For example, with all zones open and fan speed about 1200 cfm it's about .15 before the fan, about .22 before the coil, and about .12 in the supply plenum. And my anemometer says about 1200 cfm airflow thru the supply plenum. Looks like the air is moving as designed.
The manual for the furnace say an OK temperature rise is 20 to 50 degrees. But no matter how I set the zone board to stage the furnace, the supply plenum temperature gets above 120 degrees within five minutes of heat-on call (return air is about 70 degrees). It looks to me like the core problem is the fan speed is set according to the gas flow: For example, if gas is 100% of maximum then the fan runs at 100% of the speed chosen on the dip switches; 50% gas means 50% fan, and so forth. That is, I can't tell it to run the fan faster than the gas percentage.
What works OK is to set the dip switches so the furnace fan is at max for any given gas percentage, and set the target target temperature on the zone board at 120 degrees and then have the zone board overtemperature cutoff at about 130 degrees. The zone board calls for max heat at startup until the supply plenum gets near 120, which means the fan runs fast. Then the fan and the gas slow down, but there's not enough air to keep it below 130%, so the zone board cuts off the furnace while keeping the fan running, waits three minutes, and starts the cycle over again.
So, I'm letting the supply plenum temperature go 10 degrees above what it says in the manual, but on a cold night, say 10 degrees outside, the thing can barely keep up because the gas is off almost as much as it's on.
And it bugs me to be using a safety to operate the system.
Anyone know of a way to jigger the furnace control board to give me a way to set the fan speed separate from the gas flow?
Sorry for the long post. Thanks!
The problem:
No comments:
Post a Comment