Dash A/C Charge Amount 2003 Knight?

[pcallison]

Took my 03 Monaco Knight to service Dash AC.  Mechanic hooked machine to it and recharged system.  Sticker had type of refrigerant to use but did not list how much?  Any where to find that information so I will know for sure?

 

Thanks Phil

[Ivan K]

My manual says 4lbs of r134a but in my experience, that was just a starting point and one needs to go by pressures and temperatures to tune it right.

[pcallison]

Thanks Ivan,

He is an experienced mechanic that I trust.  His machine pulls out the refrigerant, measures it etc.  He put in about a pound of refrigerant to get it where he thinks it should be.

I figure that most coaches will be different.  But that is a starting point.  Thanks for the info.

 

Phil

[Tom Cherry]

My answer is NOPE....Look in your manual. For some reason, the online manuals do NOT list 2003.  Anyway, I checked a 2004 Knight. 4 Pounds R134. Curiosity...I checked my manual. SAME 4 Pounds.

NOW...here is MY experience as well as others that really "KNOW" AC's and do their own...  Here is an old copy and paste from the ORIGINAL site...and several folks have used it...as well as one that owned a repair shop

Put the dash air on the coldest temperature setting and have the air selection pulling in outside air (NOT the MAX Recirculation Setting).  With the MH’s engine  running, add R134a until you reach the following:
 
 For vehicles currently running with Freon R-134a only

OUTSIDE TEMP      LOW SIDE                HIGH SIDE                CENTER VENT TEMP

60 F                28-38 psi                   130-190 psi               44-46 F
70 F                30-40 psi                   190-220 psi               44-48 F
80 F                30-40 psi                   190-220 psi               43-48 F
90 F                35-40 psi                   190-225 psi               44-50 F
100 F              40-50 psi                   200-250 psi               52-60 F
110 F              50-60 psi                   250-300 psi               68-74 F
120 F              55-65 psi                   320-350 psi               70-75 F

The above guide lines seem to work pretty well.

I’ve found that adding R134a until my desired low side pressure is reached puts me in good shape for the year. So if the dash air is sucking in 85 F outside temperature and the low side pressure reaches 35 psig, my center vent temperature is somewhere around 45 F.

OK....that, in theory, is supposed to work. I have always had a small leak....not worth the trouble of chasing. The solution, every 3 years or so...have it serviced and put in some Freon.  LOT CHEAPER.

I had a buddy that is a graduate EE and also has taken two local Tech School courses in HVAC and has his own gages and tools as he has FIVE AC's in his house and two beach homes....so he does it himself.

It was almost 100 and HOT as blazes. We put in 24 OZ of Freon...or TWO cans.  That calculates to 37.5% of the original fill... NOW, all I can say....if it is sitting and idling...even on FAST idle, it takes a LONG time to get to the pressures....and we barely got to 35 on the low side. The air, sitting, was coming out colder...but not like it should. I was totally disappointed. BUT, when I drove it, the air flow was MUCH cooler...  It takes a LONG time for the whole front HVAC box to "cool down and stabilize".  After you drive it, the airflow, of course, does that, especially in RECIRCULATE.  So, I know that we did the same thing as the shop I was using did. I actually called our member, the expert that wrote this up.  He said that if you were inside a shop and it was early in the morning that the chart was better. BUT, if you were outside and it was hot and the MH had not been cooled down...as in running the INTERIOR HVAC, that "Your Results Would Vary".  NO LIE!

My shop was of the old school that you just added and such and I don't really know if they followed the chart, but they always got it a LOT cooler....and my 24 oz or two cans did the same...maybe a little better....

Hope this helps...
 

[Ivan K]

There is about 40' difference in the line length from a typical car system and that will play role when measuring the low pressure at a test port near compressor. I had to go by the high pressure reading and understand that the low side reads lower than it actually is at the evaporator outlet.

[Tom Cherry]

4 minutes ago, Ivan K said:

There is about 40' difference in the line length from a typical car system and that will play role when measuring the low pressure at a test port near compressor. I had to go by the high pressure reading and understand that the low side reads lower than it actually is at the evaporator outlet.

Thanks for that TIDBIT....NOW that does make sense....

[Georgia Mike]

Ivan, I just repaired a leak on mine about a month ago. I put in almost 5 12oz cans and my low side was about 25psi at 85 degrees. I think you  are correct about the pressure reading lower at the compressor then at the evaporator. High side was at the target range for outside temperature. It has been blowing ice cold so I didn’t add any more.

[Ivan K]

Mike, great, you got it figured out. If your evaporator does not freeze up, you will be good. My low pressure was about 30 psi at (I think around 90 or so degrees F) and has worked fine for probably 5 years now.

[pcallison]

Thanks men,

I did eventually find the manual to say all systems are charged at factory with 4 lbs of refrigerant.  My system was definitely low.  He did put a pound in.  Still doesn't blow ice cold but is better than it was.  He obviously didn't want to go overboard not knowing the specs trying to obtain/achieve.

Tom, that information is great thank you.

 

Phil

 

Oh, BTW it is scheduled to be 102+ here in Oklahoma for at least the next 7 days....Oh Boy...can't wait.

 

 

[Gary Cole]

I trying to wrap my head around this idea that the pressure at the evaporator is going to be lower than that read at the compressor. Seems to be contrary to what I thought was fundamental to the principles of pressure drop. Somebody explain to  me the errors in my thinking.

[Ivan K]

The other way around.

[Guest Ray Davis]

20 hours ago, Ivan K said:

understand that the low side reads lower than it actually is at the evaporator outlet

Gary, this is probably where you got tripped up on what Ivan was saying.  When I first read it I thought,  Huh

[Gary Cole]

Thanks Ray,

Somehow I confused myself with even less effort than usual. I wanted to make sure that I understood the principle correctly because I bought an adjustable evaporator thermostat so that I could play around with the low side temperature set point. My existing evaporator thermostat opens at about 45 degrees. Hoping I can lower that temp a few degrees in order to improve the feeble performance of the unit.