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Old 09-15-14, 04:24 AM   #1
F357
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Default Window unit for heater?

I have an office in a shop building that I would like to heat with a small heat pump. The heat could come from the shop area, not the outdoors, and that usually doesn't drop below 40-50 degrees.

I'm wondering if I could modify a regular window A/C unit to be a heat pump? I have an 8000 BTU unit that needs a new fan I could modify. If I used a different thermostat, and blew air from the condenser into the office, would this work? I'm thinking it would work at moderate temperature but won't work if it gets very cold. Does anybody know what the coldest outside temp is I could have and still get heat?

I know they sell window unit heat pumps that really do pump heat in the winter, but they cost significantly more. Does anybody know what makes those so much more expensive?


Last edited by F357; 09-15-14 at 04:26 AM..
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Old 09-15-14, 07:51 AM   #2
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So long as the "outside" temp is in the 40-50 F range, this would work well. Why modify? Just get the new fan and put the unit in "backwards".

Yes, moving the thermostat into your office and that is easy . . . .

I say DO IT!!

As for why window unit heat pumps costing more, it is all about volume. I bet the ratio of window AC units to window heat pumps is 100 : 1 (or more).

Let us know how it works out for you. I bet you are pleasantly surprised.


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Old 09-15-14, 02:17 PM   #3
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Welcome to the forums.

This method has been dubbed "reverse polish mode" and works so well I built a window ac heat pump after trying it.

Last edited by jeff5may; 09-19-14 at 03:22 PM..
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Old 09-15-14, 04:07 PM   #4
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Yup, like these other guys said. Just put the cold end in the shop and the hot end in your office.

It won't be pretty to look at, but effective solutions have a beauty all their own.
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Old 09-20-14, 07:45 AM   #5
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Let's just say there was an incident while I was trying to get out the old fan motor, and now my air conditioner needs to be charged.

I've always wanted to try and recharge an air conditioner with propane. Is there a how to out there anywhere for this? Everything I google is about a car. I can figure out the plumbing, but I'm not sure what I need for gauges. Can I just use a pressure gauge with the right range for the high and low side, or do I need a fancy refrigeration manifold set?

Now that I broke the seal I'm going to get a little more custom and try to make a real heat pump with reversing valves.
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Old 09-20-14, 08:28 AM   #6
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HA!! Of course, NONE of us have ever had something like this happen! But with lemons, make lemonade.

Look on these pages (archives) and you will see a lot of information on using BBQ propane. I bet some of the wizards here are better to direct you specifically.

But most of all - have fun.

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Old 09-20-14, 10:50 AM   #7
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Quote:
Originally Posted by F357 View Post
Let's just say there was an incident while I was trying to get out the old fan motor, and now my air conditioner needs to be charged.

I've always wanted to try and recharge an air conditioner with propane. Is there a how to out there anywhere for this? Everything I google is about a car. I can figure out the plumbing, but I'm not sure what I need for gauges. Can I just use a pressure gauge with the right range for the high and low side, or do I need a fancy refrigeration manifold set?

Now that I broke the seal I'm going to get a little more custom and try to make a real heat pump with reversing valves.
If you are going to venture into the fascination realm of organic refrigerants, you need to know that there are undeniable hazards involved, like fire. Be sure to acquaint yourself with recommended procedures to insure your safety. Do not do any gassing in a closed space. Go outside to work. Never do any gassing without a full face shield, and full hand and body cover.

IT'S YOUR DECISION, IT'S YOUR SAFETY.

* * *

If your original unit used R22 as a refrigerant, switching to Propane will be straightforward, since the lubricants and metering devices, etc will work.

Camping gas will work, right out of the little green canisters.

I would suggest going with the easiest project first, which would be refrigerant replacement, leaving the rest of the system intact, but changing the position of the thermostat, and also using a thermostat that will keep power on until a desired level of warmth is reached, rather that the desired level of coolness.

You will have plenty of lessons to learn... and interesting new tools to acquire.

Best,

-AC_Hacker
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Old 09-20-14, 07:24 PM   #8
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After doing a ton of googling I just want to make sure I have the basic procedure right...

1. Install service port like this on high and low side:
(Can't post ebay link, don't have enough posts here yet)

2. Hookup cheapest refrigeration gauge set I can find.

3. Pull vacuum on system.

4. Slowly fill with propane until the pressure is in the right range.

Does that sound about right? Are the high and low side pressures going to be about the same for propane? (Says 170/380 on the machine)
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Old 09-20-14, 08:26 PM   #9
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Quote:
Originally Posted by F357 View Post
After doing a ton of googling I just want to make sure I have the basic procedure right...

1. Install service port like this on high and low side:
(Can't post ebay link, don't have enough posts here yet)
Yes on this one. Schrader valves are what they're called. Be sure you pull out the valve cores before you braze (don't solder, not strong enough), then put them back in when the metal is cool to the touch.

Quote:
Originally Posted by F357 View Post
2. Hookup cheapest refrigeration gauge set I can find.
It's always good to save money, but buy a gauge set (new or used) that you have some reason to believe will work

Quote:
Originally Posted by F357 View Post
3. Pull vacuum on system.
Yes, and if the system has been open for a while, hold the vacuum for a few hours. Use fresh vacuum pump oil... not compressor pump oil, vacuum pump oil is important.

Quote:
Originally Posted by F357 View Post
4. Slowly fill with propane until the pressure is in the right range.
Pretty much so. Put in a bit of liquid propane into the hi-side port, to at least get to 0 psig.

Then start the compressor and put in GAS into the low side port with the compressor running. Don't be in a hurry.

You may need to let it run a while without gassing, to let things equalize, then you might need to add more... repeat as required.

Quote:
Originally Posted by F357 View Post
Are the high and low side pressures going to be about the same for propane? (Says 170/380 on the machine)
In my experience, they're around halfish of what R22 was.

Don't forget, this is not child's play and you are completely responsible for your own safety.

Good Luck!

Let us know how it goes...

-AC
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Old 09-20-14, 08:43 PM   #10
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Is it OK to use compression fittings instead of brazing? The service valve I found on ebay is at the end of a short piece of 1/4" copper tubing.

To be honest it's all just an experiment at this point, this thing isn't really worth fixing with used A/C units going for $25-50 all over craigslist this time of year. I might just get a bigger one for my office...

Thanks for the information!

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