Automotive Air Conditioning Information Forum (Archives)

Provided by www.ACkits.com

We've updated our forums!
Click here to visit the new forum

Archive Home

Search Auto AC Forum Archives

Farm Equipment Charge

mjohnson2981 on Tue June 08, 2010 5:13 PM User is offline

Model: 6620
Refrigerant Type: R134a
Ambient Temp: 80
Pressure Low: 16
Pressure High: 187
Country of Origin: United States

Completely retrofitted. EVERYTHING new (hoses too) except Evaporator & Condensor

It is a TXV system, fixed cooling fan. (Doesn't depend on ram air, like a car)

Factory charge is listed at 70 oz or 16 oz after bubbles disappear.

I can not get vent discharge air below 58 degrees

From about 48 oz to 64 oz, the guage readings were around 15 and 180, superheat stayed about the same, subcooling gradually increased.
At around 64 oz charge, the guage readings are about the same, but the suction line at the compressor was about 34 degrees (18 deg. superheat) 20 subcooled
At around 72 oz charge, the guage readings are about the same, but the suction line temp jumped to about about 46 degrees (30 deg. superheat) 23 subcooled
Overcharge, I know, but at 80 oz charge, the guages read about 18 and 200, suction line temp is about 48 degrees (29 deg. superheat) 30 subcooled

Am I overlooking something? The low side seams low, but I can't get it to come up. Superheat was in line, but why won't discharge temp drop below 58 if compressor suction is 34?

Any info would be appreciated.

Thanks

TRB on Tue June 08, 2010 6:34 PM User is offlineView users profile

Is the capillary tube attached to the suction line and wrapped with the tar type tape?

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

mjohnson2981 on Tue June 08, 2010 7:54 PM User is offline

We retrofitted this last year, and the "professional" ac shop that made the hoses and checked everything out said that the equalizing port wasn't needed and they brazed the hole shut. This year, we have brazed a new fitting on and put on a new externally equalized txv (from deere). Yes, the TXV, bulb, and equalization line are all sealed in cork tape.

bohica2xo on Wed June 09, 2010 2:34 AM User is offline

I am guessing that the numbers are at idle.

Open the cab door. Run the engine speed up to 1500 rpm, and run the cabin fan on high speed - with the 70 ounces installed. Record the pressures while still at 1500 rpm after 5 minutes.

Post the results.

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.

mjohnson2981 on Wed June 09, 2010 7:19 AM User is offline

The numbers are at 1500 RPM with the cab door closed, high fan speed. I will evacuate and recharge today.

bohica2xo on Wed June 09, 2010 12:29 PM User is offline

Ok, if those pressures were @ 1500 - the TXV may need adjustment or may just be defective.

You asked why the delta T was so poor with the low discharge pressures - the answer is refrigerant mass flow. Not much refrigerant passing the TXV for some reason.

Since you are recovering, pull the TXV & have a look through it. Unfortunately, adjusting the superheat means recovering the system for each adjustment on most automotive type valves.

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.

mjohnson2981 on Thu June 10, 2010 10:48 AM User is offline

Something I have noticed, but cannot understand.

There are two cabin air filters on the machine. If I remove one (it is new and not clogged), of course the air flow will increase over the evaporator. Logically, you would think that the suction line temp at the compressor would raise from more heat load. But...

With the cab filter IN suction temperature is about 53 degrees
With the cab filter OUT suction temperature is about 45 degrees... I did this several times and it doesn't make sense to me.

Can someone explain?

Thanks

ice-n-tropics on Thu June 10, 2010 3:48 PM User is offline

Johnson
Sub cool at 80 ambient temp of 12 to 18 deg. is OK
Retrofit quantity of R-134a is often 10% to 18% of R-12 factory charge for good cooling at 100 ambient
Deere typically uses 50% outside air (OSA) to pressurize the cab to reduce dust intrusion.
Maybe one filter is for outside air and one is for recirculated air.
If the removed filter reduces air flow restriction for recirculated cooler/drier air then OSA is reduced to 25% (recirculated becomes 75%) and louver temp is lowered because delta T of air remains same as 50/50.
hotrodac

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

Back to Automotive Air Conditioning Forum

We've updated our forums!
Click here to visit the new forum

Archive Home

Copyright © 2016 Arizona Mobile Air Inc.