New Carrier Econ. Control

[jeffcolledge]

I just installed some 10 ton Carrier rooftop units with econimisers. The econ. comes factory adjusted to 15% minimum position...my ass, the thing is completely closed on all 3 units! I talked to the tech support for 45 minutes trying to increase it...thats how long it took him to walk me through it. I thought things were supposed to be easier as technology advanced. Whatever happened to a little pot on the actuator? The new econ's come with a circuit board in the return air panel with two buttons on it and 4 LED lights. I figured after he walked me through the first one, and having the literature with me, the next ones would be easy...no ah ah! I can't figure them out...all I want to do is increase my min pos...has anyone figured out how to do this easily?
The M# is 48HJE012

[klrogers]

I know the board you are talking about, it is very hard to understand the instructions at first, take the manual, a mug of coffee, and a 5 gallon seat and spend some time going over it. It has so many settings it should have a port on it for a laptop, but then Carrier would want as much for the software as the whole rooftop unit.

[seaboard]

We just completed a project installing 269 of them so I know exactly what you are talking about. It will get much easier with practice. Just follow the instructions in the literature and turn off the phone to avoid distractions as you have to scroll to the right setting to adjust it. One of my guys draped a towel over his head as he worked on them so he could see the lights better in the sunlight. I'm still not sure if I like them or not but it's better than the DC motors with the slide damper and 9 volt batteries.

[jeffcolledge]

Thanks guys, I ran the risk of looking stupid with this thread, but you guys seem to understand my frustration. I appreciate your input.

[seaboard]

Because of our EMS application I had to read that manual cover to cover. If that economizer does the things it says it does, they should be great. It will allow the compressor to run on a call for Y2 but only after a time delay. It then monitors the supply temp and will cycle the compressor if the air gets too cold and below a certain ODT it will not allow the compressor to operate at all.

[jeffcolledge]

So the need for capacity control is unnecessary, like fan cycle contol?

[sparks]

I did the start-ups on 10 rtus with those economiser controllers. Thank God the factory settings were what we were looking for. I still get headaches just thinking about reading that manual again. Why couldn't they just put a 2 digit display on there instead of counting those christmas tree leds. Try it in the bright sun or on a silver roof, pain in the but. Man what a design, I will never figure that one out.

[superfittertech]

You said you needed 15% outside air & the dampers were closed. How do you do osa calculations? On a lot of units, especially ones with barometric relief dampers you're getting 18 to 20% osa with the economizer dampers 100% closed! Do the math 1st.

[hw chiller man]

You said you needed 15% outside air & the dampers were closed. How do you do osa calculations? On a lot of units, especially ones with barometric relief dampers you're getting 18 to 20% osa with the economizer dampers 100% closed! Do the math 1st.

Please explain to me how you would achieve 20% make up air with the fresh air dampers completely closed. If this is possible we could satisfy a number of commercial buildings in the north without having to heat the air.

[superfittertech]

simple math problem formula (Actually there 6 different ways to figure min osa). %OSA + % RA = MA. Example You want 10% OSA. Outdoor temp.=90 deg, return air= 70 deg. 10x90=9
90x70=63. 63+9=72 deg mixed air temp. This formula is accurate as long as there is at least 4 deg. temperature difference between osa & ra. Same formula when it's cold out. outdoor temp=20 deg, ra= 70 deg. 10x20=2 90x70=63. 63+2=65 deg. mixed air temp. On a hot day close economizer off 100% take osa, & ra temps. You'll find your ma temp higher than ra temp & use the above formula you're likely admitting 10 to 20% osa due to leakage of the barometric exhaust dampers. I teach this to apprentices & I don't know how many times I go there to check & find the dampers physically 15% open, but when I actually check temperatures min. air usually more like 20-25%. The new carrier economizers have (3) sensors in them osa,ma,& ra. So when you set them up for 15% they are usuallt 15% unless ra & osa temps are the same.

[hw chiller man]

Thanks for the answer superfittertech, I was aware of the formulas, for return air, fresh air and mixed air. However I was not aware that a barometric relief damper would actually allow air to infiltrate into the mixed air plenum. I always worked on economizers that had an exhaust air damper that was mechanically driven to interlock with the fresh air and return air dampers. regards