Economizer woes

**mike4hvac** · 03-03-2005, 06:39 PM

OK so I have this RTU, a Lennox (I forget the model # I think its a GCS 20) . I get a call the other week saying that its not cooling. Well I get there and neither stage will run when the unit calls for cooling. So I trace the problem back to the econimizer it will not open. So I trace voltage to the E control itself but no voltage is coming out of the Controller so I chage it. Boom now the econimizer works. Then all the sudden it stops working right in front of me, it wont even open when I set the minimum position to maximum. So I figure maybe (because its a little in the shade) its just cold enough to "lock out" the econimizer. So I go back the next day (now its warmer) and it works fine. I install a couple fan cycleing switches cause its cooling a server room 24/7 and I figure "hey low ambiant control may be a good move for this unit." Well I leave and about a week later I get a call again about the same unit. I get there and the Econimizer is not working again even when I mess with the Minimum Position (and its a pretty nice day'bout 60deg sunny and dry as a bone). It's a Honeywell Econimizer package, you know the type, Simple Enthalpy Sensor, Enthalpy Control and 24v Spring Return Moter. The light on the Enthalpy Board is on signaling that it is getting a signal from the Enthalpy sensor. Any clues as to why this POS will not worky worky?

**git-r-dun** · 03-03-2005, 06:48 PM

If they are using it to cool a server room why not just keep it in mechanical cooling anytime controller calls for it. Take Y terminal straight to Y2 on unit. I'm thinking they will not mind and you already put the low ambient kit which would not be really in use since under normal operation economizer would be used for cooling. Then again it would if second stage would need to come on

**fat eddy** · 03-03-2005, 08:08 PM

The light means suitable for free cooling right if I remember correctly? I beleive this the 135 ohm little black one, I have had problems with these before and it always ended up being a guesing game of which part was bad, my advice is to replace all the components that control the economizer these are relatively inexpensive parts.

**ac/dc** · 03-03-2005, 08:08 PM

I think the cust. would perfer "free"cooling from the
econo. they paid good money for. Whats the honeywell no.
on the control? does the control attach to the actuator?
min. pos. should work regaurdless of outdoor conditions
When you replaced the control the new one had literature with the check out procedure in it right? It sounds like
a bad actuator but some voltage checks need done to be
sure. Actuators dont fail very often
I think the fan cycle controls are a good idea anyway for
those 60 degree humid days when outdoor air is unsuitable.
By the way...the light on the contol indicates outdoor air
is suitable for cooling, The control will not lock out
econo even when below zero, it simply modulates to maintain disch. air temp by mixing with return air

**seaboard** · 03-03-2005, 08:11 PM

I'm not sure about the particular model you have but I'll give you some general advice. The minimum position adjustment should move the dampers regardless of whether the enthalpy switch is open or closed. It's just that, a minimum air setting. The motor should lose power to stroke closed whenever the fan isn't running but whenever the fan comes on generally the motor will have power to assume it's minimum position. If it's a Honeywell solid state enthalphy control, the light on means that enthalpy is OK for cooling. Light off, mechanical cooling should operate. If it is using the single sensor rather than dual sensors make sure the resistor is in place across the return air temp terminals and that it is good. Is this a separate motor or the kind with the board built on to the motor?

**fat eddy** · 03-03-2005, 08:12 PM

Doesn't the enthalpy switch lockout econ. ? setting it to its min pos

**git-r-dun** · 03-03-2005, 09:32 PM

AC/DC depends on what kind of customer you're dealing with. Our customers, that deal or have any type of electronics, prefer to not incoperate any outside air what-so-ever because they want to recondition air in space only. As a matter as fact they pay us to disable economizers. So "free" might not be that important to them as much as Air Quality is. I have a manual I'll look up from some Bard package units. I think they might be using the same type

**old fitter** · 03-03-2005, 09:59 PM

Disable the POS,it wouldnt be so critical if it were for comfort only,but its too fragile and variable for equip cooling.And as were pumping in all this free cooling is there a properly sized exaust fan drawing the equip generated heat off the cieling?
You could wire it in the event of cooling fail to act as a temporary backup,but I would never use qsa for this load.

**mike4hvac** · 03-04-2005, 08:13 AM

Ah yes Old Fitter....I try to explain to these "Imps" that it does not matter how much cool air I am pumping into this Server Room of theirs (it has two return air ducts and two diffusers, His "cousin [who is a tinner] hooked him up"). I also tell them that it does matter how many times you’re changing the air out in a given day. I tell them they need a hooded exhaust fan and a better layout, (and more for that matter) for their Diffusers and Return air Crates. I tell them that the unit they are using is for comfort cooling and that the designers never had this application in mind as "Server Rooms" did not exist at the time of its design date. So the unit runs 24/7/365, balls to the wall, both stages. It would be nice to have the outside air pumping in once in awhile as to give at least one stage a break here and there LOL. I LOOOOOOOVE people!

**coolairman** · 03-04-2005, 09:04 AM

Mike4hvac:

It's difficult to know from the information you provided, but I would look at the mixed air control. It could be this is defective and telling the economizer control the mixed air temp is too cold and throttling down your OA dampers.
Remember you have to evaluate the entire economizer system as a whole before you make a decision on which component to replace.

Regards

Coolairman

If it was easy anybody could do it even the hacks that would screw the OA dampers shut.

**vmc1161** · 03-04-2005, 09:22 AM

Mike4hvac; We do a number of server rooms that use economizers, it's OK if the equipment is not sensitive to changes in humidity. We use high guality filters and power exhaust and have back up units if one goes down. You have to be careful when combining econo and mech cooling, there is a great drop off in efficiency for the first stage comp. When is the mech cooling locked out and 100% econo on and what have you done for winter operation. Winter start package, time delay, cond. fan control, crankcase heaters, freeze control. Inquiring minds want to know.

Also what type of econo, there are a lot of them out there.

**Diceman** · 03-04-2005, 10:01 AM

I also just had Lemmox econo problems, rooftop unit for store in large mall, these stores never use heat by the way, too much heat load. And I agree with Eddy, change all the parts and be done with it, Lennox was no help either, unit was 12 years old, they had no record of the parts for the econo.
Since it is cold here I cranked it open and y-1 brings on the fan, y2 brings on the compressor, buys me some time till I figger out what I want to do with it.

**mike4hvac** · 03-04-2005, 07:02 PM

GOOD GOD!
I'm such an idiot......
"Remember you have to evaluate the entire economizer system as a whole before you make a decision on which component to replace."
Best advice I ever got man, Thanx. It was the Contacter. the soiniod lacked the volts to pull the Contacter all the way shut so the micro switch on the side of the contacter woulden't close most the time. Duhhhhhhhhh. Damn intermitant problems I swear.
Coolairman if your ever in Colorado I owe ya a beer.
Mike

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