5 wire to 4 Terminal Thermostat.


Old 10-31-05, 01:25 PM
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Join Date: Oct 2004
Location: USA
Posts: 255
5 wire to 4 Terminal Thermostat.

Thanks in advance for all advice.

The the heat/cool switch on my thermostat in my mobile home went south. It is a five wire setup. I installed a four wire replacement which I know should work however, When I connect the compressor wire to the cool switch it does not cut off with the fan.

The setup is a stand alone air condition unit with blower on the outside with inside eletric heat with blower. Wiring is as follows:

Yellow, Green, Red, White, Blue

The blue wire starts the compressor however it does not turn off when the outside blower cycles off. Any help with the conversion would be apprecated!

God Bless,
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Old 10-31-05, 03:40 PM
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the best advice I can give you is to head back over to HD or Lowes and get the proper thermostat and quit messing around.
Old 11-01-05, 11:02 AM
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Join Date: Oct 2004
Location: USA
Posts: 255

I did not purchase the thermostat from HD or Lowes or any other place so, why would I want to go there when I can get great advice like you gave in your post!

I do thank you for your advice however, after a bit trial and error the five wire system is now running normaly with a four wire thermostat. Thanks again!

God Bless,
Old 11-11-05, 06:06 PM
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Ok, how about 4 wires to 5 terminal t-stat?

I just bought (2) Honeywell "Vision" RTH7400D programmable thermostats to replace two existing White Rodgers mercury switch thermostats. (a 1F56W-44 and a 1F56-306). These are both running similar heat pumps with aux (emergency?) heat. On the compatability chart on the new Honeywell thermostat, it indicates that they are compatible with "heat pump with auxilliary heat". I thought I was being thorough in making sure I purchased the right ones, but when I read through the instructions, it only shows a hookup for existing 5-wire installations.

On one of our current t-stats (the -306), the wiring is as follows:
Red = R
White = WH
Green = G
Yellow = Y

On the -444 t-stat, the wiring is:

Red = RH ---> jumpers to R
White = W
Green = G
Yelllow = Y

In the new thermostat manual, it does show a jumper across the RC & R terminals, but it indicates that it's only for "conventional" heating & cooling".

I wired it up similar to the -444, leaving the jumper in place and installing the wires as below:

R = R --> but I left the jumper to RC
White = W2 / Aux
Y = yellow
G = green

In this attempt, the cooling worked, but the condensor never switched over to heating, and the heating element (aux) did come on. So the cooling was fighting the heating element. (I thought that aux heating only came on if necessary - did it do this because it was fighting the cold air??)

I disconnected the jumper, but the left the R connected to R and got no cooling. So, I moved the red wire to RC and now the cooling mode is on, but when the unit runs in heat mode, I still only get cooling with the aux heat kicking in.

The question is, can this thermostat operate this heating equipment?

I appreciate all advice, but please be reasonable about it (it's Veteran's Day and I'm an AF Veteran...). I read the box before purchasing the new t-stat, and I read the instructions, too. It just didn't tell what to do if you ONLY have 4 wires coming out of the wall. Is there a way to get the heat functioning with this thermostat?? I hate to mess around too much with it and burn it out or anything.

I do have pics of the old t-stats wiring if that helps answer my question.

Thanks in advance.

Old 11-12-05, 10:30 AM
Join Date: Nov 2005
Posts: 235
if you only have four wires coming out of the wall then you don't have enough wires to control a HP with AUX.

You either have a straight electric heat with AC, or a heatpump that hasn't worked.

What brand and model # for your unit/s?

I found no information on one of the stats you listed as your old ones, but the one I found info on is a gas thermostat (the 306).

The jumper from R to RC should only be remove for use with a two transformer system.
Old 11-12-05, 03:25 PM
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4-wire hookup to 5-wire t-stat


I thought that these outdoor condenser units provided both heating and cooling, and had resistive aux heat coils in the air handler only for when the heating system need the boost. I ran a test to try to determine that before I got the new t-stats. They are nearly always on cool (we live in Florida), so I know that they are cooling units. When I switch the original White-Rodgers t-stats over to heat, the valve outside at the condenser gets warm--> hot right away. (I had to put the old t-stats back in, so I'll confirm that again tonight.)

In addition, one of the units had frozen up like an icicle just after our AC man had serviced it about 3-4 weeks ago. Since this is in an animal hospital, I had to disassemble the blower immediately that night to clean out the coil and the blower wheel (caked with years of built-up dirt) and get things working. In the process of doing so, I did have to remove the resistive heating element in the air handler. From that I know that there is resistive heat. I ASSuMEd that was the auxilliary or emergency heat, not the primary heat source. (ouch, that must be expensive!)

Anyway, to answer your question. As for the the condenser units: One is a Fridgidare (FS3BA-030K) and the other a Gibson (GS3BA-030KA). The air handlers are an unknown type, but I would imagine they are much older than the outdoor units.

If what I hear you say is correct, what we really have is separate AC (cool only) units and "electric funace" type heat, right? If that is the case, could these same thermostats be used somehow?? And, if anyone reading this thread knows, what would be the correct programmable 5+1+1 Honeywell (or other brand, maybe Totaline) to use?? I'm trying to steer into the Honeywell because of their 1 temp degree variance. That's one of the problems with the existing mercury switch t-stat systems; they doesn't maintain the temperature very well (maybe 4-6 dwell).

One last thing, after all the searching I did do on thermostats before finally buying these ones, I would have thought that all programmable units would have auto switchover. Am I correct in ASSuMing that these new Honeywells do not auto switchover??? That again would spell the end of them, since that again was the reason for upgrading - to be able to maintain specific different temperatures (day & night - weekday & Saturday & Sunday) in an environment where you need heat at night (sometimes in winter) and cooling during the day. I didn't see it on the package, nor did I see it after thoroughly reading the install instructions.

I wouldn't have thought this was going to be such a tough decision on which ones to buy. These Honeywell's "seemed" to do it all, according to their compatibility information. Of course, that might have been the bait, and the switch is that they don't cover this one particular situation. I did look at a third t-stat at the hospital and it's a Totaline (not sure of the model), but it had 6-wires to the t-stat. That one, I am fairly certain is heat pump cooling and heating, with aux heating at the air handler. That unit was just installed a few months ago by an AC man with me assisting. Although, I didn't want to pull that t-stat since it's new, I also hate to package the Honeywell back up and return it to HD as if it hadn't been installed once...

I'm still lost trying to figure the path out through this seemingly simple problem. Can a 4-wire system be hooked up to these particular Honeywell thermostats?

Thanks for your understanding, patience, and polite responses, in advance.

Old 11-12-05, 03:55 PM
Join Date: Nov 2005
Posts: 235
What kind of Valve in the condenser?

describe it.
Old 11-12-05, 05:44 PM
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4-wire to 5-wire


I'd guess it is just one of the servicing points. When I said I touch the "valve", that's what I meant.

Old 11-12-05, 06:23 PM
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It a Friedrich....

I just opened up one of the air handlers and got more information from it. It's turns out it says it's a Friedrich "Electric Heating Furnace" model # ECB053GAA. So, now it seems like that question has been answered, I guess. It more a furnace than just an air handler with a resistive element in it.

The new question then becomes, will these Honeywell RTH7400d1008 thermostatS handle this type of heating and cooling application. And then, is there some form of auxilliary heat besides the heating element that is inside the air handler that I don't see??? Maybe we just don't have any auxilliary heat.

The Honeywell compatibility chart reads as follows:

24 volt heating and AC systems:
Single state heating and cooling ---> YES
Multistage heating and cooling ---> YES
Heating only ---> YES
Cooling only ---> YES
Furnace (warm air) ---> YES
Central Air Conditioning ---> YES
Heat pump w/o auxilliary heat ---> YES
Heat pump w/auxilliary heat ---> YES
Hot water ---> YES
Steam or gravity ---> YES
750 millivolt ---> YES
Gas fireplaces (24 volt or 750 millivolt) ---> YES
Electric baseboard heat (120-240 volts) ---> YES

To me, it looks like this covers just about everything. What makes our particular installation so extraordinary??? I can't get a single hit on Google for a "ECB053GAA". Could these things be that old that they don't exist in any of the online databases????

I supposed if I knew for certain which wire was triggering which action, I could figure this out, but I don't know enough about AC to go freeform.

Can anyone look at this situation and tell me if it is possible to wire these things up correctly to get heat out of the "furnace" and AC out of the air conditioner. And, if not, what type of thermostat does???

And if there is no aux heat, wouldnt' one of the terminals of the Honeywell actually trigger the furnace heat??? It turned on yesterday when hooked up to the AUX terminal of the Honeywell... (you could smell it in the air) One of the Honeywell thermostat terminals (RH perhaps) must actually work to trigger this furnace. Still I don't understand if our HVAC system actually have any "emergency heating" mode. Based on what I know now, it seems like they do not. I am fairly certain that my units at my home do.... They definately are heat pumps, and there is also emergency heat on my t-stats there, though I haven't tried to activate either (upstairs/downstairs) since we move in last year.

Anyway, are there any Friedrich's experts left out there??? Are they still in business??? Maybe they could answer the questions.

Last question, posed already, these Honeywell programmables dont' seem to have auto-changeover, do they?? Am I missing something?? Shouldn't a programmable jump from heating to cooling as necessary based on your settings?? Wouldn't there be an AUTO setting on the modes, then? I didn't see one. It cycles between COOL -- EM HEAT -- HEAT -- OFF - no auto. Having the fan switch in auto is not going to give me auto-changeover, is it?

If these are the wrong ones for that auto changeover application, then again, which are the right ones that handle the furnace and AC and auto-changeover? At least we could decide if it's really worth chasing them down for the added cost.
Old 11-12-05, 08:02 PM
Join Date: Nov 2005
Posts: 235
You'll have to read the book that came with the T-stat tabout the auto changeover.

But I think you should hook them up like the "Single stage heating and cooling" diagram shows.

according to the way you said it was wired to the old t-stats your wires should control the following:

Red = R = 24v
White = WH = heat relay
Green = G = fan relay
Yellow = Y = compressor contactor

you also may need a common wire to the stat, but I don't know for sure.

also you will need it jumpered to Rh and Rc if those are options on the new stat. most stats with this option come with a jumper pre-installed.
Old 11-12-05, 08:56 PM
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4-wire system to 5-wire T-stat


I'm gonna try hooking it up again right now.

What is totally throwing me off is why, if these air handler furnace units in the ceiling, are for all intents and purposes, the only heating system in the place, why do the compressor/condensers run when in the heating mode?? They both do that with the old thermostats still installed, for certain, and always have, as far as I know. That's why I totally thought they were heat pumps being used for heating and cooling and the element in the air handler was the aux emergency heat. Do you think someone hooked them up wrong at some point in the past???
Old 11-13-05, 05:50 PM
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All working normally... on 4 wires...


Thanks for your assistance. I'm sorry everyone that it seemed like I was a lugnut trying to figure my problem out, but several things happened that threw me off the track. One was the test that I had done in the heating mode on the AC. The piping definately did warm up on the compressor (getting my nomenclature correct there, too...) when I switched over to heating mode, but it could be that the compressor was in a cycle down mode or something. I don't really know. From what I have learned this weekend, I now realize that the compressor is strictly an air conditioning unit.

As for the air handlers, that also was bad nomenclature. They should (and will forever now) be called electric furnaces. No more confusion about that either.

As for the wiring, I did it as you suggested skank, and programmed the new Honeywell for conventional heating & cooling, leaving the jumper in place across RC & R with the red wire connected to those terminals, the yellow wire was connected to the Y terminal, the green wire to the G terminal and finally the white wire to the W terminal. 4 wires did the job. Which brings up another bit of confusion - the AC man said another wire must be run in order to install new thermostats because of the type of system we had. He quoted us thermostats that were 2.5 times more expensive than what I got at Home Depot. Basically I believe he was in either in error, or wanting to sell new thermostats, as both the heating and cooling are working fine now on a 4-wire setup.

Last but not least, of course, I now know that these Honeywell RTH7400D programmable thermstats are not auto-switchover thermostats. In our case, that shouldn't be such a big deal since in Florida you air condition a place like this (animal hospital) almost every day, save for a couple of months or so where you might need to manually switchover to heating overnight. It would have been a nice feature to have though, making the system totally hands-off. It's those grubby little mitts touching things that usually screw it all up...

Anyway, thanks again for your help skank. I'm sure Honeywell could have walked me through it tomorrow, but instead, it's all up and working right now. They might not have been so patient. Kudos to you for sticking with it over the weekend!


Last edited by jmkeene; 11-13-05 at 05:57 PM. Reason: correction
Old 11-13-05, 06:05 PM
Join Date: Nov 2005
Posts: 235
if you really want to find out once and for all if they are HPs or not just see how many stat wires hook to the outside unit, or open it and see if there is a reversing valve. But like I said with only four wires to the stat they couldn't have been running.

Glad it is running now.

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