Coleman Furnace (#7700B)

[SebasC]

Alright here is the deal I have a Coleman Furnace (#7700B) and it has a 2 Wire AC Box attached to it.

My problem is that i cut the red / white wire to my outside AC unit while weedwhacking (Terrible) now my heater and AC won't work anymore.

I have tried connecting them that won't work, I've looked for the so called transformer but I cannot find it or what to look for (Google is not even that friendly) So i can't check if there is a voltage level coming out (24V) to see if it is the transformer or not.

Anyone have ANY pictures or idea WHERE to look for a transformer? It is really cold in here and no other options... Help!

[Robert]

Hi,

There is a transformer inside the a/c control box.

One wire from the secondary-load side will connect to red t-stat wire to thermostat.

Other wire will connect to one of those outside condensing unit wires.

The other condensing unit wire connects to a wire from t-stat reversing relay inside the a/c control box.



Go to t-stat, remove covers to reveal wires and test across RH and W for 24VAC.


Be sure furnace switches are on HEAT and AUTO.

IF your t-stat has switches set to HEAT and AUTO.


Set temp lever at lowest setting to have a NO CALL for heat.


Go here and scroll down page to see transformers and t-stat reversing relays to know what to look for :

http://www.mobilehomerepair.com/ColemanAC.html


Click on pics for enlarged views.


Thanks,
Robert

[SebasC]

Alright if i want to check for voltage where would i put my multimeter?

[Robert]

As stated, on RH and W at t-stat.



Thanks,
Robert

[SebasC]

Im a complete noob at those terms so any pictures? Can't afford a professional at this time and my family is getting kinda cold here.

[Robert]

No pics. Red wire connects at RH and White wire to W at t-stat.

Set t-stat and furnace switches as stated and test as instructed to see if you have power.


This is fairly simple DIY with what I have given. May be best to get a friend to assist if unable to call an hvac tech.

Find someone familiar with what I have posted to help with it.


Thanks,
Robert

[SebasC]

Alright I Checked the Voltage on both Wires and there is none, can I do this before i twist the wires together that I cut too?

And if I get no voltage what is the main thing I need to replace? The transformer?

[Robert]

Go inside the a/c control box, look at the secondary-load-24vac side of transformer.

Test across the two terminals for 24vac.


IF not there, go to primary-line-120vac side and test for 120vac.


Yes, you can do this before connecting outside wires.


When you cut the wires, you probably blew the transformer.


Thanks,
Robert

[SebasC]

Replacing the transformer should be straight forward I Would assume? Just unhook the cables, place transformer and hook up the cables back the way they were before to the old one right?

[Robert]

Correct, just be sure you have it marked, take photo or video to get them connected back correctly.




Thanks,
Robert

[SebasC]

ALright hooked up, still nothing.. this sucks.

[Robert]

Did you test it for proper voltage ?


Primary-Line side = 120VAC

Secondary-Load side = 24VAC


IF you have those, then it's just a matter of wiring things up.


On the secondary-load side, one wire is 24V hot wire and the other is the common.


Common goes to one side of outside a/c condenser contactor coil.


It will go straight there or connect by wire nut or terminal strip C to another wire and go there from that point.


The other 24v hot wire goes to wall thermostat R or RH.


It too will go straight to t-stat or connect by wire nut or terminal strip R and go there from that point.


Then, from inside the 2 wire a/c control box will be a wire from t-stat reversing relay and it will go to other side of contactor coil.



It will go straight there or connect to another wire via wire nut or terminal strip Y.


White wire from t-stat goes to heating control box.


You could possibly have two transformers, one in each control box.



Hope this helps, it can be confusing, especially if you have a 2 wire set up , if you're not experienced with it.



Thanks,
Robert

[SebasC]

Well the problem with the transformer is, it does not say common on it, I've seen a few (which didn't match my old transformer) that did have it noted on there so that is a problem. PS. The outside unit is a Coleman Evcon maybe its a little helpful

[Robert]

Hi,

There are two terminals on each side.

One side is hot 120vac and other is common.


Other side, one is hot 24vac and other is common.


Take your meter and place red meter lead on one of the two terminals on Primary-Line side.

Put other meter lead to the side of the metal box.


Test for 120VAC. Do same to other terminal.


ONE will read 120VAC (HOT), other will read 0VAC (COMMON).


Then go to Secondary-Load side.


One will read 24VAC (HOT), other will read 0VAC (COMMON).



IF this does not resolve this issue, then it is time to call someone to help.


DIY with zero knowledge is not safe.



Thanks,
Robert

[SebasC]

Alright I Have found another transformer (in the furnace control box) but god that thing is old...

Basler Electronics # BE 11246 KIF 45 so I am going to replace that one with a newer one cause i see they don't even make parts like that anymore.