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alireza
02-10-2003, 08:03 AM
After, "Refrigerant Liquid returning to Compressor "
Lack of Oil is the second prevalent failure of the compressors in Bus A/C system.
Simply because I do not see using of Oil safty switch in Auto A/C units [At least in all the systems that I have seen till today in my country].

I know it is a requirement of the compressors but I understand the limitations that do not let the system designers to us an OPS in their control circuits. Such as compressor working in the minimum RPM, which cases to dropping of the Oil pump's discharge pressure.

Have you thought about it ?

Latte
02-10-2003, 08:26 PM
Hello Alireza,
I am lucky that i know a little about both sides of your'e job as i am now employed as a refrigeration engineer, but before that i was a coach driver for 5 years. I dont know where you fit the a/c condersors on the Volvo's over there but over here on the B10M's they were fitted in the 2nd luggage compartment which i think is a stupid place to put them. I must admit i think the sutrak systems on the roof stand a better chance fo getting airflow.
Do you have any high temp probs on the Volvo's if they are ounted underneath.

alireza
03-10-2003, 05:32 AM
Hi rdocwra,
That's grate that you were a coach driver before being Ref. Eng.
Roof Top Bus A/C systems are developed very much in my country
more than rear mounted or underneath mounted systems.
I have not seen AC unit of B10M and I don't know if that is equiped with Direct Drive Compressor or if the compressor is driven with an individual engine.

But the Roof Top systems has some problems.
For example long suction and discharge line, in comparison with rear or underneath mounted systems.
the compact mounting of the unit components in the Roof Top model is another problem for technicians.

The Bus Mfg. Company that I work for, have roof top model for Volvo B7R, and Volvo B12,
They have a new plan to product and I'm who encourage them to consider the rear mounted system for The new model.

I will be pleased if I know your opinions about it.

Regards,
Alireza

Latte
03-10-2003, 07:17 PM
Hello Alireza,
Only being a driver, i didn't take much notice on how the system worked. As long as it'd worked when i pushed the button i didn't care about it. I however would guess from its position on the B10M that it was engine driven as it was located immediatly behind it. Whatever the disadvantages of the rooftop systems it must be better that the system under the floor. I can remember as soon as the weather got hot the luggage compartment used to get very hot due to the position of the B10. How does it work with a rear engine then, What powers the compressor on the roof. I must admit i have never heard of any specalist companies in the UK who fit bus/coach a/c. I assume they are all done at the manufactures (Marshalls, Plaxtons ect).
With regards to a rear mount system, where would you suggest putting it. As you know with the way airflow goes around a coach it creates a low pressure zone at the rear most noticable because the rear of the vehicle is covered in dirt, if the condensor was at the back would it cause too much dirt in it.
Would be interested to hear of any a/c systems or of a website

chemi-cool
05-10-2003, 07:46 PM
HI GUYS,
NEW HERE BUT ONLY HERE. BUSES USED TO HAVE THE CONDENSERS AT THE BACK BUT FACING THE SIDE. THIS WAY THERE ARE NO LOW PRESSURE PROBLEMS. IN THE YEARS IT MOVED TO THE TOP OF THE BUS (PIPE LINES ARE NOT LONG) AND COMES AS A UNIBLOCK. COMPRESSOR IS USUALY A BELT DRIVEN .
A WEB SITE IS WWW.SUTRAKUSA.COM. I USED TO SERVICE THEM FOR A FEW YEARS.
GOOD LUCK.

Latte
06-10-2003, 08:34 PM
Hello Chemi-cool,
Just had a look on the Sutrak website, looks very good.
Havn't got much time tonight, will need to look at it when i have more time.
Still like the idea of the roof units instead of the rear/undermounts

Latte
10-10-2003, 10:08 PM
Just been on the sutrak webside www.sutrakusa.com and printed off the diagrams to look at at more detail.
What can i say, the rear mount system looks a lot easier to get at & repair, if fact looks fairly easy & straightforward.
The rooftop system however !!!!!!!!!!!!!, My brain hurts already.
Would recomend anyone having a look at the website though the diagrams under how it works are very good and worth a look

Brian_UK
12-10-2003, 10:45 PM
Just a thought with the original question but do these system not have oil separators fitted ?

chemi-cool
13-10-2003, 02:39 PM
Hi Brian,
In the case where the unit is a rooftop - no. Oil always goes down back to the compressor cranckcase. Oil shoud be added after the firs short run and if there are no major leaks in the discharge line, you should not have any oil problems. In the Bitzer
compressors which I have worked on, there is an oil pump.

To ease rdocwra mind: the compressor is allways located at the bottom usually a belt driven. Now adays they dont use a special engine only for the AC.
Chemi

alireza
13-10-2003, 07:39 PM
Hi, Chemi, Brian, Rdocwra !!!!

The Bus A/C system as a part of our working field, Needs a revolution towrd evolution.

When we take a good look to the Bus A/C system, we see many of Important things in an AC&R system that has been humiliated because of Automotive industry's limitation.

For example please look to an Oil-Pressure-Control, which we have never seen it in the Bus A/C Unit and think so :

Assume you are a Driver in a Hot line of desert, with 55C air temp. in the Outside of your Bus.
Your compressor has an oil problem. Do you refer to stop compressor to prevent of any damage to it, or you are ready to sacrifice your compressor to save your passengers and yourself
from the burning heat ?


Rdocwra, will have the best reply because he touchs my purpose.

alireza
13-10-2003, 07:45 PM
Chemi, Brian, Rdocwra,

I think I'm correct about it:

I think I had seen an Internal Oil Separator in the old Sutrak Compressors.
Because of many limitations, the new model of Sutrak compressors don't come to my country.
And I don't know if they continue their wisely design or not.

Latte
20-10-2003, 11:16 PM
If I am answering the question with my coach drivers hat on then SOD the compresor, Its too hot to worry about the compressor !!!.

Now with my Engineers hat on, the system should be switched off and the roof vents opened to try & let some breeze in until it can be fixed
OH how i miss being a driver & not giving a toss about my vehicle although most systems i can remember (Sutrak Included) all you have on the dash is a thermostat and switch so a driver would not know there was a problem with the compressor until it was too late anyway