blowing out the return

[mrcool]

saw a good one today, three year old install of a trane 15 ton rooftop, new store, the air was blowing out the return and main duct was the return, lol, is this a new thing there doing now

[sonc]

Reverse the fan rotation lol
Welcome to the jungle

[amickracing]

We had to do this once because there were no other options with out increased cost. And oddly enough it worked out better to swap return/supplies. Anyway we tried and tried to get them to clean the duct.. when they turned it on the 1st time and you couldn't see across the occupied office... they knew why we wanted them cleaned.

[madarius]

The post prior to this one is a possibility of 30%, only because this a fairly new unit and that is not what's practical or economical in the field. I would love to agree with the first post. Rotation of blower is wrong direction. The blower acts as a return and a supply fan when employed in an air handler or rooftop unit. Looks to me that the rotation is wrong.

[cynic]

Ran into that last summer not one unit... all 6 on the roof of a strip mall ducted backwards.

[umd]

A centrifugal blower running backwards will not move an appreciable amount of air. Check the amp draw on the fan motor. Doubt that a fan running backwards would move much air back down the return duct. Chances are the unit was set on the roof curb backwards or the duct installers were confused.

[tab-tech]

........ will still move air in the right direction: there will be alot less of it and current draw will be very high.
If you have air being supplied through the return duct system.........something is not connected in the right place.

[Dowadudda]

Originally posted by mrcool
saw a good one today, three year old install of a trane 15 ton rooftop, new store, the air was blowing out the return and main duct was the return, lol, is this a new thing there doing now

I don't think anyone picked up on the light hearted sarcasm of your post. I did.

[hvac69]

The blower rotation will not matter, it will still move air just less. The unit was set ass backwards.

[tab-tech]

....... told the M.C. his pump was in backwards and he said "go get an electrician to swap leads then, thats HIS problem."
I said, " No sir- you don't understand...rotation is fine... your pumps are installed backwards." Your gonna have to flip the pumps (lead-lag) around the other way."
----------------------
Never seen a an air handler installed backwards, thats a big boo-boo. Was it a roof top/ curb unit?

Had an RTU about a month ago I was called in to trouble-shoot low total air volume on. (The mech. contractor had changed sheaves twice and it was still low on total air.)
The unit had about a 2 1/2 foot gap between the bottom of the unit and where the supply/return mains drop through the building. Gas fired with Dx coil in an occupied & fully scheduled MRI wing (not good).
Call in the crane and make sure you change back to the original sheaves before spinning this baby again or you'll have more problems.
........ Ahhh, the problems of a "comfort balance" by the mechanical contractor trying to save a buck just cost em big time.
How they were able to sell the owners a "comfort balance" at a medical facility is beyond me......... live and learn I guess.

[yooper]

It's theoretically possible for it to be running backwards. 15 ton 3-phase unit. swap any 2 leads and fan will spin in opposite direction.

[m singer]

Originally posted by sonc
Reverse the fan rotation lol
Welcome to the jungle

When a centrifugal blower turns the wrong way it will still move air in the right direction. The flow will be much lower but the air moves the same way regardless of which way the blower turns.

Sounds like the unit was set on the curb the wrong way.

[coastline]

if the leads are backwards you will still have correct airflow but will lose about 50% of the airflow / intallers can't read a cutsheet aint that a bummer/ what kind of duct is it on the unit. it may be easier to swap the duct at the plenums otherwise your screwed call the shell conratctor make them fix it under
warranty

[prestiege]

Originally posted by tab-tech
........ will still move air in the right direction: there will be alot less of it and current draw will be very high.
If you have air being supplied through the return duct system.........something is not connected in the right place.


CURRENT DRAW ON THE COMPRESSOR MAYBE BUT NOT THE FAN, just had a call on a kitchen exhaust fan not to long ago, fan was spinning backwards, we took over from another comp, made fan rotation right and because duct system was completely covered in grease, motor got fried, i dont work on kitchen exhaust but knew rotation wasnt right, seems other company instead of finding out the real problem hacked it, with fan backwards pulled 4.3 amps under specs thats alot for a 7.2 amp draw motor, made fan right direction and it pulled 11 amps over spec so i dont see how running backwards would affect amps unless duct sized was highly different it still moved air in right dirrection but wasnt nearly enough to keep hoods cool

[tab-tech]

Originally posted by prestiege

Originally posted by tab-tech
........ will still move air in the right direction: there will be alot less of it and current draw will be very high.
If you have air being supplied through the return duct system.........something is not connected in the right place.


CURRENT DRAW ON THE COMPRESSOR MAYBE BUT NOT THE FAN, just had a call on a kitchen exhaust fan not to long ago, fan was spinning backwards, we took over from another comp, made fan rotation right and because duct system was completely covered in grease, motor got fried, i dont work on kitchen exhaust but knew rotation wasnt right, seems other company instead of finding out the real problem hacked it, with fan backwards pulled 4.3 amps under specs thats alot for a 7.2 amp draw motor, made fan right direction and it pulled 11 amps over spec so i dont see how running backwards would affect amps unless duct sized was highly different it still moved air in right dirrection but wasnt nearly enough to keep hoods cool

Rather than to go real deep into it, I was making a generalized statement as to high amp draw vs. reverse rotation of a fan. In most cases, a fan running backwards will deliver substantially less air flow and the amps will be high. It has to do with what type of fan you consider. (ie: forward curve blades; backwards curved blades, air foil, etc.)
The reason why, in most cases, is that because the fan is turning backwards- instead of the air being drawn through it's "normal flow direction" through the fan.....it is now working like a bastard and doing hardly anything. The air flow gets "all hogged up" at the squirrel cage and basically "restricts itself" by slamming into itself. Some air will flow in its intended direction (not much) and amps will be high.
In your case, it sounds like maybe the fan was one of forward curve blades and running backwards....where air flow and amp draw would be low.