Electric Forced Air Furnace

[Charley L. Bottger]

Originally Posted by Marc D. Shunk

No, not at all. These can be installed on any furnace to help with exchanging stale building air for fresh outdoor air. Not necessarily for combustion air, which an electric furnace obviously does not need. It's pretty normal for a heat pump AHU, for instance, to have an air-to-air heat exchanger just for enhanced indoor air quality. Of course the forerunner to the air-to-air heat exchanger was the barometric intake piped into the return. On commercial work, this can just be a motorized damper to the outdoors into the return (non-barometric) with a "percent fresh air" dial on the wall in a closet someplace. The resi one's were normally just weighted barometric dampers.

My thoughts were in relation to a normal electrical furnace with closed return. I have never observed a baromertic damper installed on a electric furnace just does not happen in this area. Now with a commercial install we are playing in a different ball park.

If you bring outside air into the return on a heat pump without a preheat you just killed your heat pump.

[Marc D. Shunk]

Originally Posted by cbottger

If you bring outside air into the return on a heat pump without a preheat you just killed your heat pump.

Okay-dokey. As the kids say, "Whatever!"

My guess is... oh, nevermind. Sounds like you've got your mind made up, and there doesn't seem to be much other interest in this topic, so I'm inclined to let it die.

[Charley L. Bottger]

Originally Posted by Marc D. Shunk

Okay-dokey. As the kids say, "Whatever!"

My guess is... oh, nevermind. Sounds like you've got your mind made up, and there doesn't seem to be much other interest in this topic, so I'm inclined to let it die.

Come on Buddy it takes two to dance. The only thing I decided about that particular furnace it needs a closer look.
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[sparksnmore]

Originally Posted by dandersen

Squirrel cage blowers running backwards still blow in the right direction, just not enough.

TRUE, been there - done that.

If the blower is running, I don't see how air can be coming out of the RA.
Seems to me it has to be drawing air in and maybe just feeling like it's blowing out.

Maybe if the blower's discharge air is completely blocked, it might be just churning air. ? ?

[David A. Andersen]

There is not enough info here to rack our brains on!

I have had more than enough fun with three phase motors running backwards because someone didn't check. It don't blow back. But low flow will freeze everything up.

[sparksnmore]

Originally Posted by dandersen

There is not enough info here to rack our brains on!

I agree but it's fun to guess.

Originally Posted by dandersen

I have had more than enough fun with three phase motors running backwards because someone didn't check. It don't blow back. But low flow will freeze everything up.

Me too, I saw a RT compressor burn up one time because it had been running the wrong direction since installation.

I bet you're on the right track there David

[Charley L. Bottger]

Originally Posted by sparksnmore

I agree but it's fun to guess.

Me too, I saw a RT compressor burn up one time because it had been running the wrong direction since installation.

I bet you're on the right track there David

Just curious what are you calling a RT compressor and how do you tell if it is running backwards

[Charles Jones]

what is the size of the return in question? how did you conclude air is blowing in and not out? placeing your hand to it can make it feel one way when it is realy doing something else. place a tissue paper to it for a real test. was it suppose to be a supply and someone put return grill on instead.turn the heat up and do you get hot air out the return grill? are their any other supplys in this room?

[sparksnmore]

Originally Posted by cbottger

Just curious what are you calling a RT compressor and how do you tell if it is running backwards

I should have typed "RTU"
Roof Top Unit, electric A/C - Nat. gas heat.-230 volt 3 ph.

By the refrigerant operating pressures and compressor amp draw.

The tech didn't read the installations and did the install during the heating season.

The compressor didn't last very long once the stat called for cooling.

[Charley L. Bottger]

Originally Posted by sparksnmore

I should have typed "RTU"
Roof Top Unit, electric A/C - Nat. gas heat.-230 volt 3 ph.

By the refrigerant operating pressures and compressor amp draw.

The tech didn't read the installations and did the install during the heating season.

The compressor didn't last very long once the stat called for cooling.

A three phase reciprocating compressor can not run backward no such thing was it a scroll compressor.

[sparksnmore]

Originally Posted by cbottger

A three phase reciprocating compressor can not run backward no such thing was it a scroll compressor.

Yes, I believe that one had a two-stage Copeland scroll compressor as I recall.

You can also tell by the sound of the compressor as well as the low head pressure, high back pressure and low amp draw.

[David A. Andersen]

A scroll can not run backwards.

It may even lock up.

No high temp at the compressor discharge.

[sparksnmore]

So are you two saying no compressor can run in the wrong direction?

I've reversed the rotation on many 10 horse 3 phase compressors in refer cars back when I worked refrigeration on the rail road.

Anyway, what ever this one was it definitely did run backwards.

[David A. Andersen]

Recips can run any direction as long as the oil pump works backwards (if it has one). OPSC will shut down the compressor in 60 sec. if the pump doesnt pump that way.

I do not like to run older compressors backwards even if you can because they were broken in and worn out in that direction.

I only reverse phase to unstick a locked compressor.