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BMC (Bluebird Motor Coach Unique Issues) If you have a unique issue with your BMC coach and it can't be answered in one of the other forums here, then this is where you can list it.....List your BMC Parts here too.

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  #1  
Old 03-25-2009
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bwinter1946 bwinter1946 is offline
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Default BMC Dash Air Service

OK, it is starting to warm up around here in Central California and at a time like this, a guy like me, starts to think about checking the dash air conditioning service.

Just curious if anyone here has serviced their BMC, R-134, A/C system.

If possible for comparison, I would like to know the following data points:

Ambient air temp
Dash Discharge air temp and what vent you measured it at (Left, center, etc)
High Pressure Reading
Low Pressure Reading
Engine RPM while checking/servicing
What setting you used on the dash switches, A/C or Max etc. I usually check with : High fan and Max A/C setting on cars.

Also keep in mind I have a '97 as I have heard there may be a difference in some years.

Thanks,
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Old 03-27-2009
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Default Dash Air

Sorry, I wish I could help you. We have a 1995 BMC and there were three silent recalls, the rear axle, the louvers on the back of the engine to let air in and out, and something to do with the dash air. Unfortunately by the time I found out about them, BB had quit fixing them. So my dash air has a problem, but I do not know what it is ( I couldn't find anyone who knew what they fixed) so I do not use it. We use our generator and roof air when on the road. Otherwise we sweat.
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Old 03-27-2009
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Default

What I recall is BB decided the dash air was not "large" enough to provide the cooling they wanted. So I think they increased the size (BTU) capability of the dash A/C. I don't think there was anything wrong in its design just the coach needed more.

Even with the dash air, I know in the California Central Valley where it gets to 105+ degrees I will be running the genny and roof airs.

I just would like some numbers to compare with mine going in.

Thanks for the reply.
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Old 03-27-2009
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FWIW, 134 should get about a 20-25 degree drop in ambient to outlet temps, no matter what system it's in. You always want to be on max AC and high fan speed. You probably can test everything at idle, but may need a couple hundred extra rpm to get max cooling, ie if you normal idle is 700rpm, you may need to hold her at 1000 rpm to truly see what she'll do. But you should get about a 20 degree drop even at idle. From what I remember doing cars, you should have a high pressure of the ambient plus about 25 for a high. I never worried about the low side much, once I got decent cooling and made sure the high wasn't out of line, the low was what it was.
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Old 03-27-2009
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Default R134 High Pressure

Quote:
Originally Posted by fxdwg View Post
FWIW, 134 should get about a 20-25 degree drop in ambient to outlet temps, no matter what system it's in. You always want to be on max AC and high fan speed. You probably can test everything at idle, but may need a couple hundred extra rpm to get max cooling, ie if you normal idle is 700rpm, you may need to hold her at 1000 rpm to truly see what she'll do. But you should get about a 20 degree drop even at idle. From what I remember doing cars, you should have a high pressure of the ambient plus about 25 for a high. I never worried about the low side much, once I got decent cooling and made sure the high wasn't out of line, the low was what it was.
Hi John,

I never worked much with R134a but I think the High side pressure on a R134a system would be closer to 2.5 times the outside air temperature.
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Old 03-28-2009
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I guess that does sound more correct. I knew the numbers 2 and 5 came into play, just could not remember exactly how though. Since I've got to do mine this spring, I would have eventually seen my error, not that that helps now! Thanks for clearing it up! That doesn't fully hold true at higher temps, though does it?

Ok, did some quick research and that's correct. You can use 2.5 times ambient as a rough guide for high side, but you should not see pressure over 240. You may have a problem if you do. This can be as simple as not enough airflow over the condensor, but you've got to check to ensure you don't damage the system. Try to find a sight glass. This will make it much easier. You will see fewer and fewer bubbles as you get the proper amount in.
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Last edited by fxdwg; 03-28-2009 at 06:40 PM. Reason: Adding info
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Old 03-28-2009
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I have seen 250 on the high side of R-134 Fords that were freshly serviced by the dealer and the ambient temp was 100 degrees. Now, to see that the engine was not at idle it was held at about 1500 RPM.

I am not sure about the R-134 of the BMC. Seems possible it could be normal. This system is much larger than a car in that my experience with autos is 3 -3.5 lbs of refrigerant is a normal amount but my BMC calls for 7 lbs.

Also in my experience, you can watch for bubbles at the dryer with the R12 but with R-134 cars it is pretty much temps and pressures as they usually use a fixed orifice/cycling clutch system as opposed to an expansion valve like R-12. Anybody know if can I use the sight glass on the dryer? Sure would be nice if that simple.

Thanks,
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Old 03-28-2009
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no use of sight glass with 134

got to use temp chart with recommended lbs

do not let high side pressure not to exceed 325 or it will pop relief valve
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Old 03-29-2009
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That what I thought about R-134. The dryer sight glass only useable with R-12 systems.

Now I need a little warmer day to check my system, only 72 today.

I'll try to post some numbers after I check mine. I hope somebody else will also.

Thanks Woody.
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Old 03-29-2009
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i just charge the system if its 72 to say 275-285 high side and ck low it should be

and see what it does 28-35
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