Central Air Conditioner not coming on... transformer bad?


  #1  
Old 06-02-10, 09:27 AM
C
Member
Thread Starter
Join Date: Jun 2010
Posts: 2
Upvotes: 0
Received 0 Upvotes on 0 Posts
Central Air Conditioner not coming on... transformer bad?

Ok, so I have an old Central Air Compressor that I'm trying to get by with until I can save the money to replace everything for 410A. The unit is a QCH30-1 by Heat Controllers Inc. I can't even find any information about it online. I have already kicked in on a couple times this spring and it cooled the house fine. One day it wouldn't come on and I went to check it out and found it humming pretty loudly, no fan or compressor noise. The house fan is still operating fine.

I have had some electrical engineering classes as part of my computer networking degree but I'm a little rusty. Here's what I've done.

1. Started with the breaker, it's fine.
2. The Contactor seems to be functioning correctly as the switch is flipping the contact on with power. I am also measuring 25V across the thermostat wire.
3. I put in a new Run Capacitor as it was cheap. I'm measuring 124V to the Herm and F when grounded to the ground wire from incoming power (Grounded to the AC Unit Casing). The capacitor is a dual phase. Also added a hard start cap inline to see if the pump was locked.

I'm not really sure where to go from here. I'm assuming that at least the fan or the pump should run being that the cap is a dual phase if it is getting enough power. I am also not clear on the fan wiring, it appears that there is a yellow and brown wire coming from the fan only even though online documentation talks about a 3rd black wire. The brown wire from the fan goes to the F on the cap and the yellow wire goes to the black side of the Contactor. The humming is coming from the contactor/transformer area.

Any help is appreciated!

Thanks,

Curtis
 

Last edited by curt2199; 06-02-10 at 09:50 AM.
  #2  
Old 06-02-10, 02:23 PM
E
Member
Join Date: Feb 2010
Location: usa
Posts: 564
Upvotes: 0
Received 0 Upvotes on 0 Posts
forget about the run capacitor and the wires of the fan motor. if you didnt move the wires or touch them then it should be fine assuming u hooked the capacitor correctly. i would check that you are getting 240v across both legs of the contactor, and then check the load side of the contactor after its been pulled in and see if you get 240v there. and that humming you hear is the contactor, its pretty common for older ones to make an insanely loud buzzing sound. let me know what you find.
 
  #3  
Old 06-03-10, 06:34 AM
C
Member
Thread Starter
Join Date: Jun 2010
Posts: 2
Upvotes: 0
Received 0 Upvotes on 0 Posts
Well it's fixed. After I thought about it I remembered only testing 120V on each side of the contactor, which at the time seemed ok since I wasn't thinking on a 220V level. Went back and checked the fuse panel and sure enough, one of the 200k amp fuses tested open. Plugged in a new $8 fuse and it started right up.

I know it's an old unit, although I'd like to find out how old. It does appear to be cooling the house down fine though. When the inspector inspected the house before I bought it he told me it was really old and was showing a 14 degree difference which was on the edge of the ok range, so I should expect to be replacing it soon.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: