Old Carrier Outdoor Unit with very non-std wiring


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Old 05-19-22, 03:53 PM
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Old Carrier Outdoor Unit with very non-std wiring

I have an old Carrier outside unit, model EC38060300 from the late 70s or early 80s, yes, that old. It's been intermittent on firing up the compressor lately actually only a few times but runs greats with strong cooling. Anyway, I always knew the wiring was screwy because there was never a "Y" or "G" connection at the system board and only one of the two 24 volt connections that would normally run from thermostat to the system board C & Y terminals run directly from thermostat to compressor(I think). Anyway, my laptop crashed with the wiring pictures just after I took everything apart and I'm trying to figure what goes where to make the AC work properly. I popped the top off of the Carrier and one of the 24V connections goes to a circuit board then to one leg of a relay. The other 24V connection goes directly in to what looks like one of the compressor pipes. Pictures will explain because what I'm saying doesn't make sense. I'm just trying to figure how the original guy wired this and made it run (it's gonna be hot this wkend!). Pictures hopefully explain things. I NEED TO FIGURE OUT HOW TO WIRE THE TWO 24V LEADS SO THIS THING WORKS. I HAVE NO IDEA NOW.

Working from left to right, follow the brown/blue 24V wires (coming in they're white/red)

The brown wire hooks into circuit brd but blue keeps on

Wires go from circuit brd to relay, blue keeps going right. Notice the burnt wire at relay (old)

Blue wire is joined with yellow wire (Next pic)

Blue joined with yellow (black tape) and goes down in unit

This shot is thru the fins on the top guard (pic 1). The 2 yellow wires, 1 of which is 1 leg of 24V can be seeing plugging to green insulator? then into one of compressor pipes.
 
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Old 05-20-22, 08:04 AM
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Welcome to the forums.

Red to blue - white to brown (incoming 24vac on cooling demand)

Although there is no polarity.... incoming white to brown is Common. Common is applied to the "delay on" timer board and is connected to one contactor coil terminal. The blue gets connected in series with a low pressure switch mounted in the refrigerant line. The wire coming back from the pressure switch goes to the second contactor coil terminal. When the pressure is too low it signifies a low charge by keeping the contactor line open.

With the age of the unit you are either low on charge, have a bad timer or a defective contactor.
 

Last edited by PJmax; 05-20-22 at 10:25 AM. Reason: added diagram
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Old 05-20-22, 09:20 AM
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Thanks for the clear explanation of the connections although I don't quite understand it. I know very little about how this works. I found some backup pics of the system board wiring and the yellow wire which did NOT go to the thermostat is connected to C on the system board. Maybe the white 24v from the Carrier was connected to the yellow wire at the splice providing a Common but I don't get how the thermostat would turn on the AC. Where would the signal come from? I just want to put it back the way it was and see if it works. I don't understand how the thermostat signals the system to turn the air handler/outside unit ON. Yellow from the thermostat was never connected at the system board. BTW, the refrigerant was checked last year and it was only slightly low, the guy said he wouldn't bother topping it off. Thanks again for the reply. On the system board you can see blue, yellow and white (humidfier) connected to Common. I believe blue was connected to Y at the thermostat but I could be wrong.
 

Last edited by kikibobo; 05-20-22 at 10:07 AM.
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Old 05-20-22, 10:12 AM
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Just because the system was ok on charge last year doesn't mean it still is.


I see your control board. I see the thermostat wiring and humidifier wiring.
Yellow on C should be creating a dead short from the thermostat.

Since we don't see the condenser wiring there is a splice somewhere where the thermostat and outside condenser connect. A picture of the thermostat wiring would be helpful.


 
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Old 05-20-22, 11:16 AM
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Understood. I'm waiting for a call for an HVAC guy. That's the problem, the splice was pulled mostly apart. I do know that G on tstat was thru the splice to G on control board. Same for W and R. What I don't know is where at the splice the wires from Carrier were connected. I remember at some point after looking at the Carrier leads, thinking how crazy it was that only 1 seemed to be connected. I could've been wrong but that's what I thought I saw. Heat works fine. The Yellow wire attached to C on control board is NOT connected to anything and was never connected to the thermostat. My thinking was that at some time at the splice Yellow may have provided the Common for the Carrier. I just don't know where the 2nd wire from that Carrier goes being that Y is empty on control board and the other wire at the tstat (blue) is connected also to Common on the original pic. On the tstat pic the only thing NOT original is the blue wire connected to Y currently connected to Y on control board. I'm not sure what if anything was connected on Y on tstat. Knowing very little, how could the AC work with nothing connected to Y on the system board. Excuse me for being obtuse but where should the 2nd 24v lead from the Carrier be attached? There was clearly nothing connected to Y on the control board on the original working setup. Thank you!
 

Last edited by kikibobo; 05-20-22 at 11:39 AM.
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Old 05-20-22, 02:11 PM
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Just FYI..... the Y on the board can run the blower at the HIGH speed.
Sometimes it the G that is high speed.

You're not being obtuse. There is a splice that is not shown in any of the pictures. I don't know where it is. The cable at the thermostat is not the same exact cable that appears at the furnace. I have not seen the outside condenser cable in any pictures yet.

The condenser needs Y and C to run. Switched (24vAC) for cool.
 
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Old 05-20-22, 03:22 PM
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Thank you Pete. That's what I've been reading everywhere so I guess I remembered wrong. So, being that the Y on the system brd has never had a wire on it AND the leads were connected defintely at the splice and there's UNconnected leads from system control C and tstat Y I'm thinking that those might have the wires connected to the Carrier. Here's a rough diagram of the layout of system control board + splice + thermostat and what wires go where.

 
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Old 05-20-22, 08:14 PM
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There is a brown two wire thermostat cable that goes out to the condenser. It has a red and white wire in it. Where is it in your system/diagram ? I don't see. If I don't see I can't tell you where to connect it.

Is it at the splice point ?
Assuming there is a two wire brown thermostat cable that you are not showing.........


You can connect the red and white wires to either of the blues. There is no polarity.
 
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Old 05-21-22, 04:41 AM
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Hi, one thing, that line voltage wiring on that contactor must be cleaned up, looks like a loose connection, the low voltage wiring, I would start by identifying the thermostat cable on both ends ie. at stat and at the furnace, then which cables go out to the condenser, post some pics, possibly changing the wires to standard colors, ie. Green on G , also looks like a yellow wire tucked back into the wall ? Yellow normally goes on Y, wiring in condenser seems correct from the inside out.
Geo🇺🇸
 
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Old 05-21-22, 09:05 AM
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Hi, I am thinking that relay board may be a TD to prevent the compressor from short cycling, not sure.
Geo 🇺🇸
 
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Old 05-22-22, 10:03 AM
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I recommend replacing the contactor and repairing the burned wire connection as Geo has stated.
 
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Old 05-28-22, 07:35 AM
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I'm having trouble getting a hvac man I trust in here to repair it. The guy I have scheduled to come did say off the top of his head that my transformer might be burnt and obviously the contactor looks burnt too. He's supposed to stop by today "1st thing" but it's already 10:30 so I don't know. The 2 previous guys that I used, 1 guy obviously didn't have a clue and the other was adamant that the only thing I could do was replace the whole system for $8000. So I'm a little untrusting at this point. The guy supposedly coming this a.m. replaced an outside unit for my brother with a used one for $1500 and it's still working well.
 
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Old 05-28-22, 08:13 AM
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Wiring

Hi, have you ever identified which wires go where? You will need to know that at some point.
Geo🇺🇸
 
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Old 05-28-22, 01:35 PM
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The contactor and the transformer (fried) have been replaced and we have got the wiring so it matches PJMAX's diagram with the 2 blues (C, Y) going to the condenser. Still no go. Could the thermostat be bad? It works for heat fine and when we put it to cool it fires up the air handler side been still no condenser. And yes, we've determined that at the tstat R+W+G go to the control board R+W+G. We now have the blue wire coming from C on the control board going to one leg of the condenser and the blue wire coming from tstat Y going to the other leg of the condenser. The guys working on it don't know what they're doing and can manually start the outside unit at the contactor but can't figure out what's wrong with it. They've been here 5 hours.
 

Last edited by kikibobo; 05-28-22 at 02:24 PM.
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Old 05-28-22, 04:49 PM
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Hi, are you getting 24 VAC to the contactor? if not try and connect the 2 wires from inside directly to the contractor removing the TD from the circuit .
Geo🇺🇸
 
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Old 05-29-22, 10:06 AM
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After waiting 5 minutes you need to confirm you have 24vAC coming into the condenser.
If yes..... the brown wire is already connected to the contactor.
Connect the wire that is on the blue wire to the other side of the contactor (purple side).
If your thermostat has a five minute delay in it..... the timer board adds another five minutes so that it takes the condenser ten minutes to come on. You can disable that timer by connecting the yellow and purple wires together. Your techs should know this.
 
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Old 06-04-22, 11:34 AM
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Thank you everyone for the responses, especially PJMAX for clear answers and diagrams that were a tremendous help in understanding the possible problems/solutions. The HVAC contractor spent almost 6 hrs here and it was obvious about a 45 min in that they didn't have a clue. The lead told me the boss said my AC needed a cleaning, that's it. Anyway, they got it working and it worked all week coming on many times but today, a wk later, I decided to look at what they did. When I removed the top, my I was quite surprised by what they did and not in a good way and I'm nervous about what the repercussions might be from what they did but what to you think??

ORIGINAL WIRING: 1 of the 24v leads from inside went to T3 on the timer board and the other 24v lead went to the low pressure switch before going back to T1 on the timer board. From there (timer board), T2 went to 1 connection on the Contactor and T3 (output) went to the other connection on the Contactor. (re: PJMAX diagram above).

NEW, "FIXED" WIRING: 1 of the 24v leads from inside goes directly to 1 connection on the Contactor. and the other 24v lead goes directly to the other connection on the Contactor. The connections back to the timer board (T2 + T3) are still there but I doubt they're doing anything.

The difference on the system control board is they added a wire at Y going back to tstat/outside unit and Y on the system board WAS NEVER POPULATED EVER. The tstat wiring is the same. The "splice", which was the problem (didn't know what was connected there), R, W, G, Y runs straight to the systems board and Y(tstat-system board)/C(system board) runs to the outside unit.

It seems they took the board completely out of the picture. I asked them about the board and they said "it's good as far as I can see". The question is what is really wrong with this thing, a bad timer board ?(I can get one cheap), maybe bad low pressure switch or would the fan still come on. Remember, when it was down the outside unit didn't operate at all, no fan, no nothing. Thanks again!
 
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Old 06-04-22, 12:33 PM
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Those timer boards do go bad. Many get removed.
Let me explain.....
That board is there to delay the contactor from re-engaging in the event of a power interruption. It reduces compressor cycling That board was probably a five minute delay. Many thermostats also have a delay but if it's a battery stat.... it won't shut down the condenser line and without the timer board..... the compressor can short cycle.

Your tech should have replaced with a new timer module which is only a few dollars.
He should have set it to 2-3 minutes.

If your contactor bypassed the low pressure switch..... that is not acceptable and dangerous for the compressor.

The top picture is with a new timer board in line. New ones are only two wires.
The bottom picture is what you should have now.
 
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Old 06-04-22, 02:14 PM
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Thank you for the crystal clear explanation. One question...I'm not sure what they tried but if they tried the bottom pic (what they should have now) is there something that could make that NOT work? I can get the exact same replacement board for $10 and install it myself IF there's a good chance that is the problem.
 
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Old 06-04-22, 02:40 PM
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If the system was low on pressure or the low pressure switch was defective....your compressor would run until the system was empty and then seize.
 
 

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