Confirm my diagnosis: t'stat vs. t'former


  #1  
Old 07-21-08, 05:07 PM
D
Member
Thread Starter
Join Date: Jul 2008
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
Question Confirm my diagnosis: t'stat vs. t'former

Hi all:

Came aboard looking for info after getting a blank display on our Carrier thermostat. Had been running A/C for a few days and noticed inside temp was not holding. In fact, I found it wasn't running at all and the t'stat display was blank.

I also found circuit breakers in both the main panel and the on-unit panel tripped. Resetting the breakers had no effect, though they did not re-trip. A visible check for broken or loose wires came up empty, and no anomalies in the t'stat, air handler or outside cooling unit and their circuit boards were evident.

The main panel automotive style blade fuse is intact, and jumping the R to G terminals at the t'stat to test the fan gets no response. So, based on what I picked up in the DIY archives here, I have either a faulty thermostat or a bad transformer in the air handler.

Unfortunately, I don't have a 24v multimeter to read voltage across the R and C terminals at the t'stat, Are there any other 'meterless' DIY tests I might do to help identify the culprit? Last, assuming it is a bad transformer, what kind and where abouts are they to be found?

Any help appreciated, thanks in advance.
 
  #2  
Old 07-21-08, 05:11 PM
The Real Deal's Avatar
Member
Join Date: May 2008
Location: Texas
Posts: 146
Upvotes: 0
Received 0 Upvotes on 0 Posts
Do you..

Do you have a secondary drain pan with a water sensing float - Or it could be a float in the condensate drain line directly. If it is active or Open,( water making the float break the control voltage) the Tstat will most often go blank. If the float is open, the float is stuck if it is dry, or if it is wet, you have a drain clog problem which the float is keeping the unit from damaging your home with water overflow!
 
  #3  
Old 07-21-08, 05:21 PM
D
Member
Thread Starter
Join Date: Jul 2008
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
No secondary drain pan, unless it is self-contained within the unit itself? The unit is in the basement and condensate drains via PVC line to the sump pump crock. I don't recall seeing any safety or float switch inside when I poked about initially but I will take another look. Thanks.

[EDIT] To confirm: no 2nd pan, no safety switch, no drain line blockage...
 

Last edited by dholly; 07-21-08 at 06:08 PM.
  #4  
Old 07-22-08, 08:54 AM
D
Member
Thread Starter
Join Date: Jul 2008
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
While I locate the multimeter, any other 'meterless' test(s) I can be doing?

Any other safety limits/switches that might have come into play?

Would either a failing transformer or thermostat blow BOTH circuit breakers simultaneously, or is that symptomatic of yet another problem?

Thnx
 
  #5  
Old 07-22-08, 03:56 PM
E
Banned. Rule And/Or Policy Violation
Join Date: May 2007
Location: Wisconsin
Posts: 7,826
Upvotes: 0
Received 1 Upvote on 1 Post
I can't remember if there is a small fuse inside some digital thermostats or not. There are so many things inside, even dip switches. I know from my own experiences with digital stats that if the power is turned off, the stat goes blank. But it will restore function once the power is reset at the breaker or throw switch. But if left off for too long, I have to reprogram at least some of the functions. But the screen is never totally blank, once power is reset.

You have nothing to lose to pop the cover to see if there is a small fuse inside that stat, if no one else responds to this thread soon.
 
  #6  
Old 07-22-08, 04:01 PM
The Real Deal's Avatar
Member
Join Date: May 2008
Location: Texas
Posts: 146
Upvotes: 0
Received 0 Upvotes on 0 Posts
It is senseless

Senseless to troubleshoot an electrical problem without a multimeter. Once you find one - It will be more than easy to figure out your problem.
 
  #7  
Old 07-24-08, 02:35 PM
D
Member
Thread Starter
Join Date: Jul 2008
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
ecman51` -

I've been in the t'stat to do the R to G terminal 'jump test' and found no fuse (or batteries). This is an older, non-programmable Carrier digital t'stat which holds the input settings on EEPROM during power outages.

The Real Deal -

Hey, not so fast! I've identified electrical problems plenty of times without a multimeter... sometimes plain 'ol process of elimination works wonders. I may ultimately need a meter to run down the potential electrical issues, but I was asking for info on any other bugaboos such as your drain pan float safety switch suggestion, or other limit trips that might not automatically rest after re-powering.

Neighbor w/ meter returns from fishing trip tomorrow. In the interim, so far I believe (sorry, I'm a pilot and like check lists):

1.) since the jump test did not work, process of elimination so far suggests in all probability a bad t'former rather than t'stat.

2.) if a meter test across the R and C terminals at the t'stat comes up empty, doing the same on the low voltage terminal block on the main board in the fan coil unit confirms either the t'former is bad or (assuming all connections are ok) there is a line break from the terminal block to the t'stat.

3.) testing the t'former 24v out red and brown (common) at the low voltage terminal block on the main board in the fan coil unit confirms status of 'former, assuming 230v AC is present (it is).

Ah, and I did find all the original 1995 install info, dutifully saved by the prior owner. This is a Carrier Model 38YRA042301 heat pump, FK4BNB005 upflow fan A-coil and FKAEH0601F20 20kw heat pack. Got an Aprilaire Model 440 whole house humidifier and Space-Guard high efficiency filter. Ratings are 12.70 SEER, 8.40 HSPF.

Best regards.

[EDIT] Located another meter, no 24v @ t'stat or t'former out.
 

Last edited by dholly; 07-24-08 at 04:00 PM.
  #8  
Old 07-24-08, 04:31 PM
E
Banned. Rule And/Or Policy Violation
Join Date: May 2007
Location: Wisconsin
Posts: 7,826
Upvotes: 0
Received 1 Upvote on 1 Post
Keep everyone updated.

What do you get across the low volt terminals of the transformer? And do you have 120 coming in to the transfomer even?
 
  #9  
Old 07-24-08, 05:50 PM
D
Member
Thread Starter
Join Date: Jul 2008
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
ecman51` -

I do have 230v to the board but transformer is dead as can be -0.00, nothing, nada, zip. Looks like a new transformer is in order. Does anyone have the p/n for a Carrier oem or compatible replacement t'former handy? The current fan coil harness is designed for transformers with leads on low voltage and 3 high voltage 208/230v connections at transformer using 3/16-in. spade connectors.

Now where are those 50% off sales when ya need 'em, lol?

Thanks
 
  #10  
Old 10-22-08, 10:14 AM
D
Member
Thread Starter
Join Date: Jul 2008
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
Help- is this x-former compatible?

Ok - so it's getting a bit chilly and the wife is getting nervous about this heat thing, ha...

I pulled the x-former and it is:

Basler Electric model HT01CM230C

BE321650GDD
PRI.208/230V 60HZ
COM-BLK.208V-BLU.230V-RED
SEC.24V 40VA BRN-RED

Q.) can I use a 110v-208v 60hz 24v 50va replacement?

Or would I be removing some overload protection that protects the board, etc.?

Can pickup in an hour at local HVAC supply for $12.00 vs. 5-days for the $65.00 on-line replacement.

P-L-E-A-S-E tell me this will work!
 
  #11  
Old 10-22-08, 02:39 PM
S
Member
Join Date: Sep 2008
Location: Long Island
Posts: 695
Upvotes: 0
Received 0 Upvotes on 0 Posts
110V/208V 50 va is OK try www.Grainger.com in your area they stock residential parts and welcome DIYrs.the primary might be multi tap,but the secondary is always 24V along with that VA rating 40 or better.might want to go with a # 3TZ69 type with a circuit breaker on the 24v side to safty that end with all that goes out into the furnace and stat and condenser.
 
 

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