HVAC Power Question

[OKnewguy]

Hey gang, I bought this all in one heater/ac unit off craigslist to use for my shop. It is self contained and will be a simple setup (if it works).
Anyway, I have cleaned the coils and was going to get a thermostat to check it out, but I am not 100 percent sure how to hook up the power coming in. Can you guys give me a hand. BTW, what is the difference between a heat pump thermostat and a regular thermostat. Any suggestions on a cheap heat pump thermostat.
Thanks, Dave

 

[OKnewguy]

Here is the pic of the wiring.
Thanks, Dave

 

[Sigarms]

A thermostat controls "stages" of heat and cooling.

A "regular" T-stat is normally single stage heat, single stage cooling, whereas a heat pump t-stat will normally have at least two stages of heating, the first stage of heat being the heat pump itself, the second stage of heat being the strip heat if the heat pump itself can't maintain the temperature desired.

Depending on the set up of the system, it is possible to have multiple stages of heating and cooling.

 

[kenmac]

If you get the programmable t.stat. Be sure to read the instructions as to how to set it up in the program. For wire size. You need to know the amps of the unit including the heat strips

 

[OKnewguy]

I understand the wire size stuff, put right now I just want to make sure it is going to work. I want to test it off of the welding receptacle that I have. I do not understand the double beakers and the jumpers that are on it to. I guess what is throwing me off are the jumpers that are on there. I have been able to find the service manual for it but not the installation manual for it. The unit is a Friedrich "The Insider" model CUHP18A050A sn 96040022 manufactured in 96. The guy I bought it from took it out of a old folks home that was being torn down. He had around 20 I think. It is really a cool concept, the unit is 100 percent contained, you attach a inlet, and exhaust for the compressor and of course your duct work return and fresh. It only cost me $50 so what the heck.

 

[OKnewguy]

BTW, thanks for the great explanation of the heat pump t-stats everyone. It makes perfect sense.
Dave

 

[kenmac]

I would say they tied the breakers together so you could run 1 wire instead of 2

 

[eepete]

Thinking out loud, little bit of guessing here: Below the breakers on the right is a standard contractor. It has a capacitor on it, so it could be running a fan or compressor. Also coming off that breaker is a small set of wires that probably goto the transformer (24V) for the unit. Now on the left side, we see that breaker going into some device, and there are no clear wires coming off of it but you can see a brown and black small wire. These probably turn the device on. You might want to check and see if this somehow goes to the resistive electric strips. Sometimes the strips use a special contractor that makes a first contact with one set of resistive strips, and a few seconds later makes contact with the 2nd strip. This breaks up the inrush current from cold strips.

If this is true, then look at the size of the wire look on the top of the breakers. It looks bigger than the wires going down to the contactor and time delay contactor. So I'm _guessing_ that the resistive electric strips and the compressor are on their own breakers and the wire loops are used so there can be one feed. That way you could feed the entire unit with a (for example, don't know the real numbers) 60 amp feed, and have a 10 KW (40A) resistive strip and a 1.5 ton compressor. If you had a single 60 amp breaker, it might be oversized to protect the compressor. So you take one power feed and break it up with two breakers that are matched for the devices they connect to.

My geothermal units use separate feeds for the resistive strips and the rest of the system so that the breakers are matched to their respective devices. I like the separate feeds because I can put the resistive electric strips before my generator transfer switch, and run the rest of the heat pump on the generator. This lets me get by with a smaller generator.

I want to stress that these are guesses that can be used to help you further trace the wiring to figure out what's going on. You will need to verify the exact way this is wired, and the correct size for the circuits. Hope this makes sense.

Pete

 

[Inspector507]

Dave, if I was a betting man, I'd bet you hook up your 240V to one of the breakers where the jumpers are. It looks like they are splitting the feed into two smaller circuits inside the unit.

 

[kenmac]

The other 1 (breaker outlet) most likely feed the heat strips.

 

[caver]

That's typical of electric heat coils. My electric furnace in my house has four heating stages broken into two circuits. They scab the motor of one of those since it doesn't pull much.

 

[OKnewguy]

Okay gang, this makes sense now. Your explanations of how the resistive heat strips are on a separate breaker make great sense. So in this situation, we hook up to the the one set and jumper just takes it over to the other to maintain independent safety for each part of the system. So I would hook the 2 hots to the first breakers the jumpers take it over to the second set and the neutral goes up to the grounding lug?
Thanks everyone for the help.
Dave