View Full Version : Scratch-built video chiller

04-06-2003, 09:12 PM
Okay, I've got my 24' of .031" cap tube in, and right now, running a 10"Hg vaccum, R-409A, I have a minus 45F evaporator with a minus 12F return gas temperature.

I'm about 130F going in to my condenser

100F out.

Much like the R-404A Prommie retrofit, I don't seem to have much subcooling, of course my shop is 95F.

My discharge pressure is about 140psig, which puts the high side saturation at about my condenser outlet temperature. I've got 6' of the 24' cap tube wrapped around the suction.


04-06-2003, 09:25 PM
10"hg is minus 33, not minus 45.

Evaporator can't be colder than SST.

Liquid line temp can't be warmer than SCT.

Calibration time?

Maybe you should have started with 100'... or .026. :D

04-06-2003, 09:40 PM
hmmmmm my PT chart only goes to 5"Hg (-22F). But that makes sense, now because when I use my Fluke surface probe, the -30 department is what I read. I think the Solid state thermometer whose sensor is inserted into a well on the evap, needs some calibration. :)

I started looking for a PT chart that would go to colder temperatures... I got sidetracked. :(

Thanks, Gary for opening my eyes on that issue.

I'll see what Donebalp wants to do... If he wants more from It, I'll change out the cap tube.

04-06-2003, 09:52 PM
Try this:


04-06-2003, 10:05 PM
I'm wondering how much different the numbers would look in an A/C environment? It might tell a whole different story.

04-06-2003, 10:15 PM
Hmmmm... R409a has a huge glide, so the calibration may not be so far off after all. Maybe its auto-cascading in there. Interesting.

04-06-2003, 10:16 PM
I've gotten the thermometer calibrated and I was thinking ....:rolleyes:

I once had an old-timer working for me, who told me about some old systems in which the expansion device was, say a 1/4" copper tube with a series of "pinches" in it. The "Tech" would start pinching the tube, going down the line until he reached the proper pressures. What if instead of me changing the entire cap tube, I just added a lenth of 1/4" copper after my drier, and started pinching it to the desired conditions in order to compliment the cap tube?


04-06-2003, 10:21 PM
Are you the same "herefishy" who doesn't patch cap tubes?

You have 76' of cap tube left. Stick it in there.

Just kidding. You don't need that much more. :D

04-06-2003, 10:24 PM
Gary,............. are you telling me to STICK IT ? !!!! :eek:

04-06-2003, 10:26 PM

04-06-2003, 10:31 PM
I think the first thing I would do is find somewhere there is an A/C to work on it. Got A/C in your office?... or your work truck?

I would then patch in (yes patch) another 24' and start from there. You can always replace it when you are done.

04-06-2003, 10:34 PM
Gary, I think you're telling me that I need to work on air conditioners... and give this up.

You're playin' with me, aren't you ?

04-06-2003, 10:36 PM
I was reading your mind about the interim splice :D

04-06-2003, 10:55 PM
Originally posted by Gary
Hmmmm... R409a has a huge glide, so the calibration may not be so far off after all. Maybe its auto-cascading in there. Interesting.

Oh, d*mn it, ! :eek:

But what the issue is, is the thermometer bulb well is welded to the outlet side of the evaporator. The outlet is configured as an accumulator. I first justified the variance from the actual surface temperature that I was reading with my Fluke, to the fact that my evap may still be somewhat flooded with no load, and that a lot of the evaporation was taking place in the accumulator (return) section of my configuration.

The glide of R-409A I believe is about 9F. :rolleyes:

But then again, the referenc on the PT chart is the dew point. I conclude that your first observation is correct. ;)


04-06-2003, 11:08 PM
In truth, I'm more concerned about the high side numbers. What are the condenser air in and air out temps?

05-06-2003, 07:04 AM
Okay, Dern - it!!!!!!!

We nailed it at 64' of .031" cap tube

-47F SST


suction temp 7" from compressor -22F to -30F

... and I don't care about anything else...... :o

discharge temp is about 140F or so....

My shop is 90F at this time aproximately... (I don;t care)

with the 64' of cap tube, we could not get below the -40F mark with 409A, but hit the bottom with 404A at about minus 47 ot minus 48.

But I think that my unique evaporator design with a 3/32" copper plate between the chip and the expanding refrigerant will result in great efficiency.

Furthermore... I conclude that the great efficiency of my superioir design is responsible for the superficial results of the analysis of the end results affected by the astronomical rate of heat transfer to the ambient of the atmosphere to which it was exposed. :D :p

We'll see what happens when cranked-up in the Confuser.... but we have certainly tweaked the capacity of this JFC1 compressor to the outer limits of the envelope of its anticipated (or furthermore projected) capacity.... :)


05-06-2003, 09:27 AM
-47F SST = 1psi

64' of .031 cap tube

Something is very wrong here.

Let's imagine (and I'm not saying this is the case) that your high side guage is totally out of whack on the high end. That in reality there is plenty of subcooled liquid and a very high pressure stuffing it through 64' of cap tube.

Or maybe a totally different scenario. Who knows?

We can't tell what's going on without all of the temperature measurements.

Suction line temp
Liquid line temp
Cond air in temp
Cond air out temp

05-06-2003, 02:19 PM
Hi Gary.... if you notice the time of that last post... we were tinkering with that thing until very early this morning... :(

The SSt is NOT -47F, that is my evaporator temperature. I was running an 8" vacuum.

SST ' 8"Hg equivalent
suction return temp = -15
liquid temp 95F (approx)
discharge temp = 125 (approx)

the ambient was about 90F

....My gauges are good.... I think my condenser is oversized (it was pulled from a junk 8gph water cooler and has a 4W unit bearing motor blowing over it)

I'm going to take a nap.

I may play with it again, and get some real numbers..... It's about to storm, and i don't think it will get over 80F in my shop, today.

see ya'

05-06-2003, 03:24 PM
R-404A 8"Hg vacuum

return gas temp at cpompressor minus 15F

discharge pressure = 170psig

condenser entering discharge line temp = 111F
condenser liwuid line out temp = 82F

condenser air in temp = 80F
condenser air out temp = 83F

05-06-2003, 04:40 PM
We're not really getting what we wanted out the set-up. Donebalp decided he is going to cool the pelt with the refrigeration ( measley -45 to -48)... that should get him to -60F. ;)

We didn't do too bad considering I just put together some stuff around my shop. But we are limited by the compressor that we are utilizing.

Since I know I can build the block, I may put a little cash into something "real".... either that or put grill gas in it. LOL

05-06-2003, 05:35 PM
R-404A 8"Hg vacuum

return gas temp at cpompressor minus 15F

discharge pressure = 170psig

condenser entering discharge line temp = 111F
condenser liwuid line out temp = 82F

condenser air in temp = 80F
condenser air out temp = 83F

SCT is always the highest temperature in the system, just as SST is always the lowest temperature in the system.

Since the refrigerant warms the air, the SCT has to be higher than the 83F leaving condenser air.

You might hook your high side guage to a stable jug of R404a to see if the pressure matches the temperature. On the low side guage, you could hook it up to your vacuum pump and adjust for 29"+.

An alternative way to find SCT is to poke a thermometer through a 3" cardboard disk into the center of the condenser. Hold the cardboard up against the fins to block airflow.

05-06-2003, 05:57 PM
Originally posted by Gary
Since the refrigerant warms the air, the SCT has to be higher than the 83F leaving condenser air.

.... the fan motor is heating the air too.

My temps are taken with a fluke surface thermometer with direct contact to the copper.

You don't trust me do you? :p

I have great confidence in my pressure manifold... They are a TIF 4-port manifold with sightglass in the manifold block and glycerin filled gauges. The lowside gauge is brand new.... since my (now unemployed) ex-apprentice blow up my lowside whilst using the nitrogen bottle. :eek:

Gary, it seems like you just want to know all this info from posters so you can bad-mouth their equipment. :p

As far as SCT.... my discharge pressure is 170psig. Now that is the pressure out of the compressor discharge, NOT pressure at the condenser outlet (if we want to compensate for some pressure drop.

..... okay I'll check my highside gauge calibration.

05-06-2003, 06:24 PM
An oversized condenser throws things off. It is not possible to get 10-15F subcooling if SCT is only 5F over ambient.

Something you might want to try is blocking condenser airflow until SCT is 20-25F over ambient and then see how that effects the subcooling.

Of all the instruments we use, I trust guages the least.

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