134A sight glasses

[jack14r]

My 05 coach has 134a OTR air with 2 sight glasses in the evaporator bay,should both red balls in the sight glasses be floating,should both the glasses be clear?I have 16 degrees of temperature differential at fast idle,how much should a 134a system have?

[Jon Wehrenberg]

Jack,

The sight glasses in my coach look impressive but are of no assistance. Sometimes the ball is sitting on the bottom, and other times depending on whether it is cycling the ball is right up to the top.

FWIW at about 85 degrees I had suction of about 43 psi and about 150 on the high side.

My discharge air temp at the vent next to the passenger seat was about 65, and on the driver's air about three degrees higher. I may have a mixing valve on the driver's air leaking a little coolant to explain the slightly higher temp.

[jack14r]

Thanks Jon,The balls seem to have a mind of their own.Today it was 80 degrees here and I had 35 and 150 on the gauges with 55 degrees at the output on the OTR air,I did not check the dash temperature.Based on the chart that Prevost has on their web site I should have 45 and 158 today according to the numbers I entered into their chart.I wish the sight gauges would tell me something.what are they for?

[Jon Wehrenberg]

I have no clue what those sight gauges are for unless we both are overcharged.

They do not run in the middle on mine, being either empty or full.

I would say the pressures and temps are fine. I know I can hang meat in mine. Our AC was running about ten minutes or so when the temps were checked so maybe we could get lower, but from driving I can tell you I have to run my temp setting up about 25% of the rotation up off the coldest setting and even there it may get too cool. I think you have a digital set point on yours.

[wrongagain]

here are a couple of web sites I have directed some of my former employees to hoping a picture would be worth a thousand words.

http://www.refrigerationbasics.com/1024x768/charging1.htm

http://hvac-talk.com/vbb/

[Joe Cannarozzi]

Ed Thank you for that post. Access to a site like that second one should be volumes of help for a novice like me.

[dreadnought]

I had my refrigerant dryer filter changed because the color of the sight glass indicated moisture in the system.
This a process that took about 5 hours since you have to remove the freon, change the cartidge, pull a vacuum on the system to suck out the moisture, then put the freon back. We watched the sight glass for 4 hours waiting for the color to change & it never did. Gave up, fired it up & it changed to the right color, (pink?) almost instantly. With motor on fast idle, AC wide open, Bottom ball should be at the top, top ball should bob up off the bottom of the glass like a fishing cork when a crappie nibbles on the bait.

[jack14r]

Thanks for all the help,I especially like Bill's description of the red ball and cork.I will hook up the gauges today and look at the balls again now that I know the top one should be bouncing.

[wrongagain]

To look at truly moronic screwups look in the "wall of shame" section on the hvac talk web site.
Most of the stuff there falls into the :eek: YIKES :eek: category.

[jack14r]

As I suspected there was too much freon in the OTR system,Bill your description of the cork was right on.I was able to measure 18 degrees of differential when I got the charge corrected.I know r12 will perform better than 134a but does anyone know how much better it really is?Thanks for the help,this is the best it has performed.

[Jon Wehrenberg]

Jack,

That's a trick question. The 134 system should be different than a 12 system such as a larger condensing coil.

But a rule of thumb thrown around by folks when converting from 12 to 134 (not changing the system) is that there is a 15% loss of efficiency. I don't know if that is factual or lore.

[jack14r]

Jon,I think that 15% is real close,I remember that a good r12 car system would have 22 degree differential.I am pleased with the OTR in my Liberty thanks to everyone's help.By the way I had a friend who was at a cruise air service center in Virginia pick up a cruise air service manual for me a few weeks ago.When I took delivery of my Liberty I commented that the AC did not seem comfortable and the guys checked them out and reported 15 to 18 degrees of differential.Since I have the service manual with the pressure charts I decided to check the 2 front AC units,they were both overcharged,both of them now have over 20 degrees of differential.After that success,I decided to take out the outside TV,grill,refrig,and cabinet to gain access to another one,the fourth one is behind a panel in the first bay.My results are the same,both were overcharged,the one that does the bedroom has 18 degrees of differential and the other one has over 20 degrees.I guess the bedroom might be less because the compressor is about 25 feet from the bedroom unit.The service tech.in VA told my friend that cruise airs are very sensitive to the level of charge.It is amazing how much water condenses now that the freon charges are correct.The humidity inside seems quite a bit lower now and the comfort level is much better.Thanks again for the help.