View Full Version : Blower too small for coil
We replaced our old oil furnace (feh!) with a nice new Bryant 355MAV-042080 gas unit (yay!). Now we find out that the contractor put a 3.5 ton blower under the existing 4 ton AC/HP coil. How bad is this? What's the effect of this in cooling mode, freeze-ups due to insufficient air flow?
Could this have been avoided? What would need to be changed, the fan, motor, both?
06-23-2005, 05:58 PM
don't go by tonnage....call and see if it's a matched system. If not then you have a complaint. Many different combo's out there. Get your numbers off of each piece if concerned....however low airflow can cause a freeze-up.Has this happened?
Call whom to see if it's a matched system? It's a Ruud/Rheem AC on a Bryant furnace.
It did freeze for low refrigerant after the install, but hasn't since, although it hasn't been very hot.
06-23-2005, 07:00 PM
Whats the model number of the outdoor unit.
Outdoor unit: UPFA-048JAS
06-23-2005, 07:20 PM
You'll lose alittle sensible, and gain in latent heat removal.
In other words, it may not be able to pull the temp as low, but it will keep the humidity lower.
If 4 tons was alittle over sized for your house, you will be more comfortable now.
You can click on the bulls eye, and see what size a/c your house needs, and address your concerns with your contractor with this information, if your house needs the full 4 tons.
06-24-2005, 07:38 AM
Look up Rheem/ruud online.....website should have info for contact. Low charge will cause it to freeze, but the hotter it get's the pressures will actually raise in the unit. If they corrected the charge, you should be fine.
The fan data chart and actual duct External Static Pressure(ESP),will determine if you have enogh air flow or not.
I'd find out now ,before you have a problem.I don't seee how we can tell you without the correct information.
06-24-2005, 11:12 AM
The outdoor unit model number (UPFA) indicates this is a RUUD heat pump.
Is this system configured as a fossil fuel system?
Does the outdoor unit run during the heating season?
If so, there may be an issue of low airflow during the heat pump mode of operation.
Is this system configured as a fossil fuel system? Does the outdoor unit run during the heating season?
It used to be dual-fuel. Now it's set up to for gas-only in winter.
I'll work on getting the real numbers.
This issue came up because the coil pan rusted out, so the coils need to be replaced. I assume that the coils are designed to match the outside unit, but what would happen if we replaced the 4-ton coils w/ 3.5 ton coils? Otherwise, how would I get more CFM from the Bryant? New motor, new fan?
Guys, where i'm at, we run a 450 cfm per ton for cooling here. Our SHR is usually in the low .80 to mid .80s, residential.
Just imagine a 2.5 ton blower on a 3 ton A/C system here. it wouldn't fly here. and if we added all the static, we've probably need a 3.5 ton blower here.
If cris's a/c is correct, then it is possible to freeze, but then again, cris might be able to get away with cooling and dehumidifying depending his location.
Cris, it would be better to get a pro to check out your sensible heat and latent heat to see what your system is doing.
You don't want to hurt your compressor, BTW do you have a TXV at the coil. This really helps.
I'm in W. Oregon. It's not usually hot, but if it is, it's dry (<30% RH).
do you have a TXV at the coil. This really helps.
I don't know, but remember that the coil is about to be replaced (rusted pan). I'll take that as a recommendation for TXV on the new one.
IIRC, the Bryant is blowing 1225 CFM.
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