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E/V chamber

cthamalis on Fri March 07, 2008 9:24 PM User is offlineView users profile

Year: 1940 ?
Make: Blue - M
Model: Humidity chamber
Engine Size: 1/3 HP
Refrigerant Type: R-12
Ambient Temp: 68-72
Pressure Low: 16
Pressure High: 125
Country of Origin: United States

Hi, I was hoping someone here could lend me some in-sight into this thing, I asked about this unit when Tim first got this new website but I cannot find the original post. It was originally designed to cycle high humidity to low humidity and so forth, but we only use it to cycle cold /hot cold hot, for stress testing instruments for cold solder joints temp sensitve components, component drift, ect.

I thank those who responded last time, you guys here helped me figure out that the expansion valve was bad in this unit & I replaced it.

It has been working great until about a week ago,( 7 years !!) the compressor locked up. I have installed a new one today, & it's been awhile since I charged a system, & I have a question, should the suction line get all frosted over ? if the charge is correct ? I am nervous about overcharge, and liquid locking the new hermetic unit. (500.00 mistake if I do.)

view of whole unit



view of actual "" box I'm trying to heat/cool ""




under the "" floor "" is a bunch of heating elements to heat it up




Referidgeration Compartment



the 2 solenoids are on the left after the drier the left one picks the regular expansion valve the right one picks the "" blue "" valve they are controlled by a switch on the control panel under the time wheel that you can see in the first pic. we leave it set to the expansion valve solenoid. The grey box on the right in front of the comp/cond is not used, just there because it is !!( we bought this from ebay and the small pressure tube was broken when we got it, I don't know what this thing originally had in it from it's factory, so it's totally a re/engineer it thing.

so my question is is the suction line supposed to frost completely over or is that just a sign of low charge and/or should I keep charging until the sight glass is clear of bubbles ?or is the frosted suction line a sign I am overcharged and starting to get near slugging the comp. with liquid ??

All we want it to do is cycle from -10 C to + 50 C over and over again.

just some more information about it, the referidgeration just runs and runs pulling out x btu per hour, so it gets cold, but when we cycle it hot, all that happens is the heating elements under the floor over power the referidgeration to make it go hot, until the time wheel says go cold, and then the heat just cycles off until we want it to go hot again.


thanks for listening

Cthamalis


Edited: Sat March 08, 2008 at 12:45 AM by cthamalis

NickD on Sat March 08, 2008 10:32 AM User is offline

Guess I never heard of a chamber calling for refrigeration and heat at the same time, usually one or the other, as I recall, strange things happen in an evaporator when you bring the chamber temperature up to 300*C with some type of a relief valve. If your questions can't be answered with the service manual, would get Blue M on the horn and ask them, these things aren't cheap.

ice-n-tropics on Sat March 08, 2008 1:29 PM User is offline

Suction can frost over if:
The TXV is opened wider than the conditions call for
The system is undercharged (Ps is abnormally low). Ps = 16 is not too low for light evap heat absorption at 70 ambient
Cordially,
Old IV guy

-------------------------
Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod

bohica2xo on Sun March 09, 2008 1:18 AM User is offline

Uh, looks like it is operating properly to me.

The desired specs are -10c, and he shows a low side of 16 psi with R12. Just about perfect I would say.

Of course the suction line ices up. The gas leaving the evaporator @ 16 psi / -10c are well below freezing, and should collect moisture from the air at that point.

The hermetic compressor is probably warm enough to deal with a good bit of liquid droplets into the case, but I doubt that will ever happen. The suction line at the compressor is probably close to 0c.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

cthamalis on Sun March 09, 2008 11:23 PM User is offlineView users profile

Thank you for the replies !!

I since have spent another 6 hours on this thing !! ( well not all of them actually having to work on it probably about 4 of them in observation... ')

Changed around the liquid line ( I diddn't like the little elbow before the solenoid valves, it looked crimped), The sight glass is 3/8 flare and the liquid line was 1/4 flare and it Being a Sunday, impossible to get 1/4 ones, I decided to put them in the suction side for observation purposes, and replaced the liquid line with a solid piece of 1/4 copper, as shown in the pic below, less connections less chances of leaking.



Also I have pressures !!!

table below

the room ambient is 68-70 deg by climate control

box temp ==== press low ===== press Hi

40 deg C 104 F --------- 35 psi 168 psi

32.7 C--------------------- 31 ------------- 160

26 C------------------------ 27 ------------- 150

22 C ---------------------- 25 ------------ 145

16 C ---------------------- 21 ------------ 134

12 C --------------------- 19 ------------ 125

0 C ---------------------- 11 ------------ 110

-5 C----------------------- 9 ------------ 100



When I recovered the charge to change out the liquid line I got back a half pound, I wasnt sure if the 1/4 to 3/8 adapter on the outlet of the receiver was leaking and I wanted to clean it up, installed the dryer/sight glass in the suction line so I could use it as a window for liquid, and better than not having any drier in the system whatsoever, I then sucked it down for an hour and charged 1.22 lbs R 12.

stopped because the suction was frosting over and the box temp was 16 Deg C. I recoverd about .11 lb, and just observed the system for awile, kept tweaking the charge to finally be about 1.1 lb. +/- a high pressure hose full.

now when it hits -10 C the suction line just frosts to just before the sight glass as that is what I tweaked the charge to be +/- the high pressure hose full.

I mean that when I went to remove my gauges, I would close the service port to the high pressure side of my gauge set first then open both wheels to let the high press hose back into the system, and it would be too much and fost all the way to the comp, so I would just fill the high press hose again and then recover my gauge set, ect, ( ie +/- a hose full) then just add a hose full at a time of low side gas until I got it to just frost the suction line until just before the sight glass.

Could I safely resume ignore mode ?
(well, other than taping up the pipe insulation...)

what do you guys think ???



Thank you for your time

Cthamalis



Edited: Mon March 10, 2008 at 12:16 AM by cthamalis

NickD on Mon March 10, 2008 7:34 AM User is offline

This still doesn't sound right!

"just some more information about it, the referidgeration just runs and runs pulling out x btu per hour, so it gets cold, but when we cycle it hot, all that happens is the heating elements under the floor over power the referidgeration to make it go hot, until the time wheel says go cold, and then the heat just cycles off until we want it to go hot again."

You are only heating to 50*C, what if you were heating to 100, 150, 200*C to the pressures in your system with the compressor running? Compressor would lock up as the evaporator is red hot at those temperatures. It's been almost 40 years since I worked on a Blue M, can't remember the circuitry, been thousands of circuits since then. But do recall once you reached the low end of your cycle, the compressor should switch off before the heaters kick back on. You must have a shorted thermostat switch or relay someplace. Those solenoid valves have something to do with that, some kind of bleed off, I don't remember. Kind of recall some kind of time delay at the high end where the heaters kick off, fan air cools the inside of the box down before the compressor is allowed to kick on again at some preset point. Would check out your control circuitry.

Ironically, we would run products 10,000 cycles between -50*C up to 160*C to see what happens to whatever is inside the box. At the same time, the temperature chamber is also being cycled 10,000 times, stuff does go wrong.

Recall failure rates at around 3,500 cycles due to thermal expansion and contraction, some subtle changes had to be made. The more recent solution was to only cycle at 3,000 cycles, and people wonder why they have problems today, have to keep the stockholders happy.

bohica2xo on Mon March 10, 2008 11:26 AM User is offline

So, now the sightglass is in the suction line, and it no longer frosts the suction. A giant step backwards. I fix process controls, and that mess looks good for a house payment right now...

I can't understand why you are worried about the suction line frost. Your chamber temperature is below freezing, and it is reasonable for the line to be as cold as the evaporator discharge.

Now you have no sightglass on the liquid line, and are not charged properly. "Tweaking" the charge is not how that system is controlled.

The "gray box" is a temperature control - but the capillary tube appears to be torn off of it.

The black cylinder to the right of the compressor is the receiver, and it has a capacity near 2lbs of R12 liquid. The tiny bit of refrigerant in your charging hoses should have an immeasurable effect on system performance. You are riding the line on critical charge right now, with the TXV wide open. When you add .25 ounces it actually starts to cool...


B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

NickD on Tue March 11, 2008 2:04 PM User is offline

Gee bohica2xo, seems like you are implying to find the problem and correct it as opposed to modifying the system. But isn't the latter a lot more fun?

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