Heating, Air Conditioning, Fridge, HVAC/Carrier heat pump problem


I have a Magic Chef Ultra II 90 furnace model EC6F100DC16-2 and a Carrier Model 38YRA030300 heat pump.  When the burners turn off on the furnace, I lose the 24 volts going the thermostat for about 45 seconds causing the display on the t-stat to go blank.  I have measured the loss of voltage at the transformer.  I disconnected all the leads from the furnace to the heat pump leaving only the 24 volts from the transformer to the t-stat (red and blue) and the white lead from the t-stat to the furnace.  The furnace operated correctly without the loss of 24 volts and only a ‘trouble’ indication on the t-stat so I am thinking the problem is in the in the heat pump.  Do you know what could be causing this to happen?   

Thanks in advance for reading my question and for any help you may be able for provide.

 The only way you could loose 24 volts at the transformer and then get it back is if the high voltage lead to the transformer is interupted.  On the furnace board you will find a spade labeled L1 and next to it XFMR.  That is where you check.  L1 is line voltage in from the home and XMFR is high voltage straight to the transformer.  They are connected always, unless you have a bad solder joint on the control board.
 The thing that worries me is the "trouble" light on the t-stat with everything unhooked.  That should only light up with 24 volts coming back from the heat pump.  So, all in all I am pretty sure it is the thermostat.

Heating, Air Conditioning, Fridge, HVAC

All Answers

Answers by Expert:

Ask Experts


john t. borgman


I am in Portland Oregon at Ben's heating 503-233-1779. I work days, so I can only answer early in the day or later in the evening. I only answer public questions for residential equipment. I am very well versed in gas, electric and heat pumps and will only answer residential applications. I have been known the past decade or so, by my employers as the guy you send when no one can figure it out. Trouble shooting is my special. I understand the physics behind air flow, refrigerants and electricity. I understand programmable t-stats, zone controls, economizers, fossil fuel kits and the engineering thought process in the wiring and construction of residential equipment


I was lucky enough to start in this field almost 30 years ago as an installer, for a company that installed the best duct systems I have ever seen, even to this day. The best ,as far as understanding the way air really flows through a duct system, from the return air to the very last supply register . They also had great pride and the duct work was put in, not only to last 50 years, but to look exceptional. Then as I started doing service work, I was again fortunate that I found a 3 year engineering class being put on be a man that was the educational director for the Entire united states for a society called " the Refrigeration Service Engineering Society " And for the next 3 years I schooled at night and practiced what I learned during the day, a great advantage over schooling and then trying to remember it years later.. Versed in duct design manual J heat gain/loss calculations.

Refrigeration Service Engineer's Society

I have 2 inventions that have gone through the process and been recorded at the National Institute of Standards and Technology from start to finish and thus been invited to national innovation workshops by the dept. of Commerce and the dept. of Energy. They are waste heat recovery devices that N.I.S.T approved as valid and am currently looking for marketing partners to get this product into the hands of consumers and make a BIG difference in Energy savings for every Household and Eatery and take a big bite in the the peak hours power consumption that face our Utilities companies.

factory training in Lennox ,Rheem, Ruud ,Trane, Tempstar ,Carrier, Day&Night, Payne, Bryant, Coleman, Intertherm, York, Goodman, Ultra boilers, Unico, Mitsubishi,Sanyo, Taylor, Nicewonger, Navien. Associates degree in Refrigeration Engineering. Certified with Energy Department, Check-me Program, P.T.C.S (performance tested comfort systems ), have N.A.T.E. certifications in gas, a/c & heat pump.

©2016 About.com. All rights reserved.