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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 282
Experience:  I have been an HVAC/R mechanic/technician for 30 years.
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i have a carrier hvac unit 48tff004-511 model rooftop package

Resolved Question:

i have a carrier hvac unit 48tff004-511 model rooftop package unit with and economiser installed on it and need to know the proper way to wire the thermostat so the ac will work.
Submitted: 1 year ago.
Category: HVAC
Expert:  Brian HVAC Guy replied 1 year ago.

Brian HVAC Guy :

Hi, I'm Brian. I'm here to answer your HVAC question to your complete satisfaction! Are you receiving my chat message today?

Brian HVAC Guy :

I see you are standing by, are you receiving my chat message?

Customer:

hi brian how are you today

Brian HVAC Guy :

I am doing great thanks!

Brian HVAC Guy :

That Carrier unit is best controlled using a multistage cooling and heating thermostat. What type of thermostat are you trying to connect and how many conductors are in the thermostat cable?

Customer:

the unit is a gas/electric with 2 stage heat and 1 stage cooling with the economiser

Customer:

the stat is a honeywell programmable stat with 2 stage heat and cooling capabilities

Brian HVAC Guy :

That is correct. I have looked up the model. Even though it is just a single stage cooling unit, when you add in the factory economizer it should be wired as a two stage cooling unit to Y1 and Y2 so the thermostat can call for mechanical cooling when in the economizer mode and the economizer is not keeping up with the cooling demand. 2nd stage cooling would then bring on the compressor in addition to the economizer.

Customer:

the cable is 18-8

Brian HVAC Guy :

so you would wire R, G, Y1, Y2, W1 and W2 and if the thermostat needs a common also C

Customer:

have it wired red to r and rc.

Brian HVAC Guy :

That is correct since it is a single transformer system.

Customer:

i wired it to standard wiring on the connector board with y1 and y2 from the stat to the y1 and y2 on the unit and it blows the fuse on the control panel

Brian HVAC Guy :

Is this a new installation?

Customer:

i was looking on line and it said the gray wire from the economiser is to run to y2 ?

Brian HVAC Guy :

And by fuse, are you referring to the low voltage fuse on the units control board?

Customer:

yes 4 amp fuse on the board

Customer:

if i disconnect the stat and jump from r to y2 the compressor starts fine

Brian HVAC Guy :

are you jumpering R to G, Y1 and Y2 with the thermostat wire disconnected?

Brian HVAC Guy :

I am looking at the diagram now btw

Customer:

i programmed the stat to the 2 heat 2 cool settings and ran new stat wire from the unit to the stat. this is a replacement unit that i bought and it was in operation four 3 months before i got it. it was removed because the inspector said it was to small for the building it was on after they did renos. so they installed a bigger unit

Customer:

just jumped from R to y2

Brian HVAC Guy :

Ok thanks. Yes the diagram I am looking at has grey coming back from the econ to Y2 on the terminal board.

Customer:

the unit has been running since Dec but we haven't needed the cooling just the heat, so the first time it went to cooling it blew the fuse

Brian HVAC Guy :

I'm sorry not going back to the terminal board but to the outdoor fan relay

Customer:

and where does the Y1 hook to?

Brian HVAC Guy :

and I'm sorry again I read the schematic wrong. The gray wire is y1 and goes to OFC and CC1

Customer:

i am in Calgary Canada and the spring sucked that's why i am just discovering the problem

Brian HVAC Guy :

Ah Im about as far north as you are in Maine!

Customer:

is there a wire coming back to the terminal board to y2 ? and how does it turn on the compressor

Brian HVAC Guy :

Let me have a closer look

Customer:

or do you just run the y1 on the stat to the gray wire and the economiser turns on the compessor

Brian HVAC Guy :

The economizer has internal contacts that either bring the 24v signal from y2 back through the grey or orange wire depending on whether the econ is running or not. If econ is running it will send the Y2 signal back through the orange wire to bring on the first stage compressor and condenser fan, if the econ is not running it will send the Y2 signal back to the gray wire for the second stage compressor on units with two compressors.

Customer:

ok now i am confused....so from the stat you hook y1 to the grey wire and nothing on the terminal board????

Brian HVAC Guy :

No, you should be able to just hook the stat to Y1 and Y2 and the econ should do the rest. I am betting there is something awry in the econ that may be blowing your fuse.

Customer:

that is the way i hooked it up in the first place

Customer:

and what do you do with the gray??

Brian HVAC Guy :

Wow I'm sorry my dyslexia is showing. It's the grey wire that comes back from the econ plug that goes to the OFC and CC1 and is either given power from Y1 or Y2 depending on whether the econ is on or not. The orange wire will do nothing on your unit as you don't have a second compressor.

Brian HVAC Guy :

If you were to disconnect the econ at the molex connector and jumper pins 2 and 4 (blue and gray) and the unit runs ok then the problem is in the economizer. If the fuse still blows then there is an issue in the unit control panel.

Brian HVAC Guy :

I'

Brian HVAC Guy :

I'm sorry I fat fingered that, it should be pins 2 and 5!!! (still blue and gray wires)

Customer:

i will give that a try and get back to you, it may take a while, is that ok?

Brian HVAC Guy :

Yep that is fine, I will just save the question and I should be here if you have other questions.

Customer:

ok i will be about an hour or so

Brian HVAC Guy :

No problem, good luck!

Customer:

thank's for your help with this

Brian HVAC Guy :

You are most welcome.

Customer:

hey raining hard here will do the tests when it stops

Brian HVAC Guy :

Ok sounds good. I have to go for a bit but will check back in later. I have found most time that the problem with economizers tend to be the damper motors or the Enthalpy Control (EC) Since you got the compressor to run I'm pretty sure the fuse blowing issue will be in the econ.

Brian HVAC Guy :

Do you have the manual for that unit? I will post a link to it if you don't.

Customer:

Hi Brian, hooked up the y1 stat and y1 on the terminal board left the y2 disconnected and it seems to work ,so will run with that for now and will get back to you if i have problems

Customer:

thanks for your help and the manual ,it was a great help.

Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 282
Experience: I have been an HVAC/R mechanic/technician for 30 years.
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