I hope I can solve this inexpensively and maybe learn something in the process before I have to shell out for the local pro. Any advice or help is greatly appreciated:

Problem: 11 yr old Payne Heat Pump system stopped working last week. Dead, nothing works, not heat, emergency heat, cooling, nor fan. Weather was fine that night just cold, so lightning was not afoot.

The last time it was working that evening my wife had gotten up to raise the heat slightly and she recalled the blue light (resistance heat) coming on. A couple hours later I noticed that the house was cold, the room temp was well below the set point and the system was not functioning at all. I did not notice any of the circuit breakers tripped either.

I took the following checks/corrective measures:
1. Got into the Payne air handler and checked the small 5A fuse (a usual suspect) with multimeter but it was fine.
2. While in the air handler I noticed a great deal of corrosion around the ground lug to the chassis, probably the result of all the moisture that can build up in the air handler in the humid summer months here in SC. I cleaned this up thoroughly, replaced lug with a fresh copper one, reconnected the bare ground wire, and coated all with OX-GARD grease. I did not see any other locations of corrosion or other suspect connections in there.
3. I checked the 50A and 30A Circuit Breakers for Heat/AC in the house breaker box and they were at 124V, which is OK.
4. I checked the pair of Buss 30A cartridge fuses in the box on the outside wall near the heat pump unit. Only 0.3 ohms, so they are OK. That means the Heat Pump has power from the AC Voltage mains.
5. I took the cover off the old White Rodgers 1F58-58 Thermostat in the house and checked the small wires on the front side around the coil for continuity and they seemed fine. I did not have a very small screwdriver so could not remove the whole stat from the wall for a closer look. Also know nothing about what voltages to check for on the stat or the conditions under which to check them.

None of the things I did were able to get the system working again. I am stumped - I suspect the stat, but need some advice with what to look for. Maybe it is something elsewhere in the system like the air handler or the contactor or heat pump. I sure hope its not the compressor.

 

You should check for power with one lead on each pole of the breaker, NOT from each leg to ground. If this is how you checked then you have a breaker, or incoming power problem.

You should have around 240vac

If you can get to were the wires ties into the thermostat check for 24vac with a probe on R and a probe on C or X.

Let us know.

 

Thanks for the reply and the help, Steve. I will try testing the voltage across the breaker and looking for 240V. If it checks out then I will test the 24V on the stat.
If it turns out that the stat is bad, I would like to replace it with a programmable one. Are they generally interchangeable across most makes and models of heat pump systems?

 

Usually not a good idea to give electrical troubleshooting info but you sound like you have some experience just be real careful, you will notice that old seasoned techs move very slowly and deliberately around hot circuits, one wrong move could fry you and your unit. Lets take a shortcut, go to the contactor coil and give the contactor center section a gentle push in with a quality insulated screwdriver (Klein preferred), if the unit starts let the center section back out, Now assuming that the unit did start set the thermostat to call for heat and check for 24 volts at all wires on thermostat to C list the ones that are 24 volts to C and check your specific thermostat to see what should be energized for heat (always R if transformer and wiring is OK) probably G for blower fan and maybe a W for heat and maybe something else for the reversing valve all manufacturers seem to do their own thing. If everything checks out there go to your furnace and perform the same voltage check with the thermostat wires, if everything good there go to your transformer and check for 240 volts on primary and 24 volts on the secondary side (most use 240 volts primary direct from the contactor coil 120 volts from each side and are 10 to 1 which reduces to 24 volts secondary) ONCE AGAIN BE VERY CAREFUL YOU ARE WORKING WITHIN FRACTIONS OF A INCH OF VERY HIGH VOLTAGE!! now if good there simply check for 24 volts at the contactor coil if 24 volts there simply replace the contactor as the coil is bad. If no voltage at contactor coil and ythe trans and wiring and power to contactor are good you may have to spend a few bucks as at this point you may want to call in a PRO since any further checks will require factory info typically only avaliable to a licensed tech. Probably the defrost board but it should not be replaced unless checked (typically the recommended way to check is to trade it for a known good one LOL)

 

Thanks DNT for your advice also. Well I know enough about this to be dangerous. I appreciate the warnings. Since it is dark and cold and rainy, I am not going to tackle the contactor tonight.

This is what I did so far tonight:
1. Checked breaker box. Got +240 on all my AC and Heat related breakers.

2. Took front plastic piece (the part with bimetallic coil attached) off the base board of the thermostat. So what I have remaining mounted to the wall is a plastic base with a small circuit board and 8 colored wires coming out of a hole in the wall and attaching to the board by screws at various points.
With the breakers on and the thermostat switch calling for heat (but nothing working of course), I checked for AC Voltage at the C reference to all other 7 wires. Got nothing.

So this tells me that the stat isnt getting any juice at all. So it is probably not the problem? Or is this test only valid if the system is running? Does this mean another trip into the air handler to check all those wire nuts for bad connections or corrosion?

Also, and I should have mentioned this last night: I have noticed on occasion since last winter of frost building up on the outside coil on especially cold nights. When I saw you mention a defrost board, could this have failed, first to be unable to effectively defrost the unit and later to completely disallow the unit to operate?

Thanks in advance to DNT and Steve for all your help.

 

If you have nothing at the thermo stat you probably have a blown trans former, or fuse.

If it is the transformer you should put in a 3A fuse on the secondary side when you replace it.

To check open furnace and check for 24vac from the red stat wire to the brown stat wire.

As always use caution when working on live electric curciuts.

 

Should I set the stat so its calling for heat when I do this (red wire to brown wire voltage check)?

Also should I try replacing the 3A fuse at the transformer first and see if the system works, before determining the trans to be fried?

 

if there is a fuse there then yes by all means change it if it is blown.

Doesn't matter if unit is on or off as long as the main power is on you should have 24vac from red to brown.

 

Steve,

So if measuring across the red and brown wires does not show 24VAC then either the fuse on the secondary side of the trans is blown or the trans itself is gone?

Would it be easier to just replace the 3A fuse on the tranformer?

Just to make sure I go to the right place to check this, is the transformer inside the air handler or on the heat pump outside unit?
There is a 5V fuse on a board inside the the air handler (the gold-color two-prong flat blade type fuse with the Z-shape element inside) that I have already checked out and found to be OK. Is this different than the transformer fuse?

Thanks Again

 

Sorry, my last question was dumb - of course the transformer is inside the air handler, otherwise there wouldnt be heavy gauge black and white wire and bare wire for ground from the AC mains in there. It is hanging from the ceiling of the airhandler in a small compartment behind the blower motor. Very hard to get to to make measurements on. The 5A fuse I mentioned earlier is plugged in there. It is easy to get to, being on the cover panel side of the board. This fuse blew once before a few years back causing a similar problem of nothing working. But this time this fuse looks and tests fine. I guess the transformer is finished. Am I right on this conclusion? Is there a way to first verify that it might be something else more serious (Like defrost board DNT1 spoke of) before I replace the trans?

 

Universal 10 to 1 transformers are cheap but will require some knowledge to cut/splice factory wiring. Factory transformers are typically hard to get and expensive but will usually be a exact replacement and plug right back in, if wiring skills are a bit weak you may want to pay the additional dollars and order a factory OEM replacement if avaliable. Your local pro can wire you a universal in in just a few minutes I would probably have the capacitors changed out at the same time as a preventative maintenance item, they are also cheap. Note thermostat wires can be easily damaged by chipmunks and such, they seem to like to eat the exposed insulation cover. I would check for 24 volts on the secondary at the transformer itself to verify it is bad before ordering a new one, might just be a broken thermostat wire between the trans and Tstat. Blower typically comes out pretty easy and that should let you access the transformer. Figure all day and take your time if you finish early yeah. I spent half the night last night doing a plumbing project (changing out a washer dryer outlet box) I quess I saved a couple hundred bones but man sometimes it just does not seem worth the effort especially after three trips to the hardware store. I quess the satisfaction of knowing it is done right outways wasting hour upon hour messing with stuff that I have minimal knowledge of LOL Besides what else is a man to do? TIMES ARE HARD AND MONEY IS TIGHT

 

Having some crow for dinner tonight. I called the pro today as I was stumped about this problem and also concerned about the defrost cycle. While I checked the cartridge fuses that were on the outside wall near the compressor it seems I forgot to notice the two cartridge fuses that are under the house near the airhandler. They were mounted in a box that was out of the way on the far side of a floor joist and so in all my checking around never traced up to them. Tech replaced both of them. $117 bucks, the most expensive fuses I have ever bought. At least the system is working now and house is warming up.

He also checked the defrost circuit and it seemd to be working fine. He said my freon is low but he cannot find any leak with the freon sensor. He is not allowed by law to add any more freon if a leak is suspected. He suggested its likely in the coil in the air handler, which would be $800 to replace. System is 11 years old and I hate spending dough like that for a patch. Something about putting new wine in old bottles.

At least I have some time to shop for a new system over the next year or so. Carrier's Infinity looks good, also considering going with geothermal but I dont know how well that would cool the house in SC summer.

Many thanks to you DNT1 and Steve (Shank) for your help and guidance on this, I am relieved it wasn't something more major and I learned a lot in the process. Merry Christmas to you and your families.

 

Glad you got it going again MW and you are very welcome for the help. One thing, the information the tech gave you is not exactly technically correct about not being able to add refrigerant. On residential systems under 50 lbs refrigerant capacity there are no EPA rules preventing a tech from doing a gas and go, although it could be that the company he works for has that particular policy in force, heck I like it. Save the whales/penquins etc. and keep it green man.