How to-- install CO2 sensor in a Carrier 48 series RAC

[dngrsone]

Yes, it sounds like an infinitely stoopid question, but... I'm a freakin' controls guy, not a doctor; and I just spent three hours on the roof watching a supposed Carrier tech talk on the phone to his Carrier rep, trying to figure out how to wire in a four-wire CO2 sensor so the machine will run.

I'm looking at a Carrier 48AWT035BD RAC and I am wiring in a CarrierCO2 Sensor Part no. 33ZCSENCO2.

The electrical diagram on the RAC shows me wiring the power wires into TB4 1 and 7, which we aren't disputing-- the sensor is obviously getting power.

However, the diagram shows me connecting pin 6 on the sensor to TB5 pin 7, and pin 7 of the sensor to TB5 pin 6. What's more, there is a 120 ohm resistor installed in between TB5-6 and 7, and the diagram says specifically to remove the resistor if using a potentiometer for remote economizer control, but doesn't say anything about when wiring in a powered CO2 sensor.

The Carrier rep on the phone says to remove it, because we are using the 4-20ma capability of the sensor, and it is therefore not needed, and the two of them argued for a couple hours over what AQ.AC should be set on-- 1, 2, 3... WTF?

We finally gave up, disconnected the sensor for the time being and went to lunch.

So, does anyone have any insight for me before I go back over there and smack this guy upside the head with a BFH? I'll be more than happy to sneak over there, wire the sensor in and program the machine while the other guy isn't around, but I'd like a little more knowledge before I try.

[jrbenny]

Here's the controls IOM.

http://www.xpedio.carrier.com/idc/groups/public/documents/techlit/48_50a-4t.pdf

I'm reading it now for your answer.

[jrbenny]

Well, I don't see AQ.AC as a point in the software. Is it working now? If you must return, the IAQ config points are on page 157. The explanations begin on page 28.

Good luck. You'll need it. I hate the new version of that software.

[Balibe]

The website shows the optional co2 sensor part number for a 48A to be CRCBD10X002A00. Not saying the 33ZCSENSC02 wont work as both provide a 4-20mA signal.

I do know the 33ZCSENSC02 needs a dedicated/isolated power supply to work. Basically if you dont have a seperate power source and need to power with the same power source that powers the controls you need to use a 24vac/24vac isolation transformer. The dedicated power source is stated in the CO2 Install Manual and missed by alot of people. Polarity is also critical as you have 4-20mA, as you are a control guy you probally have already checked that.

The 182ohm resistor needs to remain unless you are using remote setpoint, which appears you are not.

I would also check to see of the FIOP Return Air IAQ was shipped with the equipment, may have been installed at the factory and the ACC C02 Space Sensor shipped with the unit. Dont think you can use both as the same input.

AQ.AC is an incorrect table, you need - Configuration →IAQ →AQ.CF →IQ.A.C. -. You want option 1 ... [1 = IAQ analog input] for a standard input. There may also be other tables you may need to adjust for proper operation. The link that JR posted to the Controls IOM lists all the tables.

[dngrsone]

Thanks a lot guys! Sorry about the table confusion there... I wasn't exactly taking notes at the time...

I believe that the CO2 sensor is wired directly into the RAC for power, so I guess I will have to hit someone up for an isolation transformer or wire in a separate power transformer... maybe my installer has a spare bouncing around... :argh:

You know, I was absolutely certain that resistor had to stay put, I just couldn't see anything in black and white that said so.

Yes, only one option installed for IAQ... we're supposed to be installing a carbon monoxide sensor as well; not idea where that will plug in, but I'm not going to worry about that.

Again, thanks a lot guys... I feel not-so-stupid now. :)