Ac not working

Reply

  #1  
Old 05-17-14, 09:36 AM
Member
Thread Starter
Join Date: May 2014
Posts: 8
Received 0 Votes on 0 Posts
Ac not working

My AC system is not working. Checked the thermostat, quick disconnect and power (240V) to contactor is good. However there was no low voltage to contractor. Inside at furnace/ac control board the fuse was blown and I replaced. At the 24COM connection on the board there is no low voltage (24 volts). Correct me if I am wrong but this indicates a bad board? There is power on the low volt side at red ® just not at 24COM. This means the 24 low voltage relay is good but a problem in the board right? Checked the overflow and it is cleared and working. ANY ideas? If it is the board can I jump low voltage from the R at control board to 24VAC COM tip i get the new board? Never worked on AC so any help would be much appreciated
 
Sponsored Links
  #2  
Old 05-17-14, 09:42 AM
Bob14525's Avatar
Member
Join Date: Jun 2013
Location: USA
Posts: 1,470
Received 11 Votes on 8 Posts
Why did the fuse blow? They don't normally blow for no reason. The purpose of the fuse is to protect against a short on the 24VAC circuit. You mentioned that there is no voltage at the 24COM terminal on the board. Where are you reading to (where did you place the other voltmeter lead)? The 24COM is the return (ground side) of the 24VAC circuit. You should measure 24VAC between the R terminal and the 24COM terminal. What do you measure between the R & COM terminals?
 
  #3  
Old 05-17-14, 10:24 AM
Member
Join Date: Jan 2014
Location: USA
Posts: 699
Received 0 Votes on 0 Posts
Also , find the 120 - 24 VAC transformer . Do you have 24 VAC at the secondary side of the transformer ?

Did heat work this last winter ?

God bless
Wyr
 
  #4  
Old 05-17-14, 10:25 AM
Member
Thread Starter
Join Date: May 2014
Posts: 8
Received 0 Votes on 0 Posts
Not sure why the fuse blew. Turned on the AC and the fan came on but no AC unit. first thing I check was the fuse and i was blown. I misunderstood that was the ground side. I thought the 24VAC COMM should have voltage. I checked it against unit ground. When i measure the R against 24VAC Comm i get 26 volts. So then that checks good. Any other ideas why I am not getting power to contractor switch?
 

Last edited by Aduvall; 05-17-14 at 10:25 AM. Reason: misspell
  #5  
Old 05-17-14, 10:28 AM
Member
Thread Starter
Join Date: May 2014
Posts: 8
Received 0 Votes on 0 Posts
reply

Yes i have 24VAC at transformer and I do get heat.
 
  #6  
Old 05-17-14, 10:44 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 52,689
Received 343 Votes on 321 Posts
When you put the thermostat in cool you should measure 24vac from C to Y.
If you don't.... it sounds like you have a thermostat problem.
 
  #7  
Old 05-17-14, 11:39 AM
Member
Thread Starter
Join Date: May 2014
Posts: 8
Received 0 Votes on 0 Posts
reply

i get 24vac when the thermostat is on cool and check R to COMM. Blower is running just ac unit is not
 
  #8  
Old 05-17-14, 11:42 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 52,689
Received 343 Votes on 321 Posts
When you put the thermostat in cool you should measure 24vac from C to Y.
R to COMM just tells you the transformer is working. We need to test further.
 
  #9  
Old 05-17-14, 12:00 PM
Member
Thread Starter
Join Date: May 2014
Posts: 8
Received 0 Votes on 0 Posts
I found splice in the low voltage wires where the wires exit the house. I have power at the spice just not at the contactor switch when ac is turned on at thermostat
 

Last edited by Aduvall; 05-17-14 at 12:45 PM. Reason: Spelling
  #10  
Old 05-17-14, 01:39 PM
Member
Thread Starter
Join Date: May 2014
Posts: 8
Received 0 Votes on 0 Posts
Any ideas

Any ideas? Power coming into ac unit looks like it travels through a circuit board then to outside leads of contactor. No power at contactor. What should I check next?
 
  #11  
Old 05-17-14, 05:12 PM
Bob14525's Avatar
Member
Join Date: Jun 2013
Location: USA
Posts: 1,470
Received 11 Votes on 8 Posts
When you say you have power coming into the outside (compressor/condenser) unit, if you mean you have 24VAC, then you need to either look at the wiring diagram (if there is one), or trace the wiring to find out why you have 24VAC coming into the outside unit, but it's not getting to the contactor.

Some compressors have low or high pressure switches, or a time delay relay in series with the 24VAC going to the contactor. If your compressor unit has any of these, you need to check to see if they are open. The pressure switches safeguard the compressor in case the refrigerant pressure is too low or high, so if one of these is open, don't just bypass it (at least not permanently). If it's the time delay relay that's bad, you can safely bypass it if you have a digital thermostat, as that has the time delay functionality built into the thermostat. Since you said that the 24VAC connects to a circuit board, it likely is a time delay relay, however the wiring diagram (usually on the inside of the outside unit cover), should identify what it is.
 
  #12  
Old 05-17-14, 06:00 PM
Member
Thread Starter
Join Date: May 2014
Posts: 8
Received 0 Votes on 0 Posts
Reply

Thanks for the information. There is power (24 vac) coming into the unit and I see that the issue is that a switch or relay is open somewhere. You right either low or high pressure switch but not sure which.
 
  #13  
Old 05-18-14, 03:07 AM
Bob14525's Avatar
Member
Join Date: Jun 2013
Location: USA
Posts: 1,470
Received 11 Votes on 8 Posts
You can temporarily jumper the switch, or check with an ohmmeter, to determine which switch is the problem. If it's a pressure switch that appears to be the problem, you'll have to call a professional (licensed HVAC contractor), as you need to be EPA licensed to work with refrigerant. Were you able to find a wiring diagram for the outside unit? If so, it should show you what switches are present in your unit. I'm hoping that it's a time delay circuit that's bad (may be the circuit board that you mentioned), as that is easily "fixed" by jumpering around it and using a digital thermostat. I had to do that 20 years ago when the time delay relay went bad in my Bryant A/C unit.
 
  #14  
Old 05-18-14, 03:35 AM
Member
Join Date: Jan 2014
Location: USA
Posts: 699
Received 0 Votes on 0 Posts
From what you have said , were it me , I would turn off the 240 VAC to the outside unit .

Next I would replace the wiring from the splice , all the way to the inside of the condenser unit . But do not tie it into the control wiring of the condenser unit , yet . Insulate the new wires inside the unit . Make the splice , where the wires exited the house ( secure , well insulated and water / weather proof ) .

Replace the fuse , with the same amperage , voltage and type ( slow blow / fast blow ? ) . If you have not already done this .

Turn the indoor system & tstat on & select cool . Indoor fan should come on . Is the new fuse OK ? If so , go test the new 24 VAC wires inside the unit ? Do you have 24 VAC ?

If not , you have a problem with the wiring between the tstat / furnace and the outside of the house .

If you have 24 VAC , turn everything odd . Visually check all the 24 VAC wiring inside the condenser unit ( with the 240 VAC OFF ) . Look for bare , frayed , broken or loose wiring . Less likely on 24 VAC , but possible , burned wiring .

If all looks OK , tie your new 24 VAC wires to the control wires of the unit . Turn the indoor unit on , tstat to cool . Did the contactor inside the condenser unit , close / pull in ?

If it did not , check to see if you still have 24 VAC at the new wires you installed ?

If the contactor closed / pulled in , turn the tstat to off , restore the 240 VAC to the condenser unit . Turn the tstat to cool and see what happens ?

God bless
Wyr

PS If you have a pressure switch bad , follow the advice given by the other messages , to address that problem .

But you will have to solve the issue of why the fuse on the control board blew . Hint , buy at least one spare fuse . They probably are inexpensive . It is good " insurance " .
 
  #15  
Old 05-18-14, 08:45 AM
Member
Thread Starter
Join Date: May 2014
Posts: 8
Received 0 Votes on 0 Posts
I bypassed the board and it looks like one of the switches is open. So either way looks like I must call an HVAC tech to replace the switch or find leak. I just serviced last summer so it looks like I might have a slow leak somewhere and low pressure is probably the issue. The system words cause I also bypassed the manually pushed contactor for it ran fine for a few seconds until I released it. Just bought the house before last summer so who knows how long this was an issue. Not sure what caused the fuse to blow.
Thanks for everything
Aneta
 
  #16  
Old 05-18-14, 11:12 AM
Member
Join Date: Jan 2014
Location: USA
Posts: 699
Received 0 Votes on 0 Posts
Sounds like you have decided the switch is open because of low refrigerant pressure ? If so , the switch may close properly , when the unit is recharged ?

God bless
Wyr
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


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