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Topic: Freon Capacity of the A/C system ? (Read 899 times) previous topic - next topic

Freon Capacity of the A/C system ?

Dave Cobb's question (IRV2) on amount of freon in the a/c system reminds me when the tech at Tenn RV started checking my a/c system, 1st was remove all freon, 6.7 lb. was surprised saying it should only hold 5.9 lb (I think).  Found problem with the pressure switch on compressor, replaced it, when refilling the freon, he installed the 5.9 lb, it worked but not where he wanted the numbers & duct temp.  When he got happy was when all 6.7 lb was back in, duct temp dropped to 48f at idle rpm and both hi & lo presure were in correct area. My point is knowing the capacity of system is just a starting point for the techs that know the game. MO.

Re: Freon Capacity of the A/C system ?

Reply #1
I've been trying to find the "official" refrigerant capacity (R134A) of our A/C system.  I don't see it anywhere in the Owner's Manual or documents I received with the coach.  Nothing at Beamalarm.com.  Anybody have that number off the top of their head?

I believe ours is "low" due to rapid cycling of compressor, but haven't had the opportunity to get it checked by a qualified tech.
Chuck, Jeannie & Bella the MalChi
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"It goes without saying..."

Re: Freon Capacity of the A/C system ?

Reply #2
Chuck,

In 1993, the dash A/C used regular Freon R12.  Yes, someone may have converted it to 134A.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Freon Capacity of the A/C system ?

Reply #3
One of the POs converted it.  It is clearly marked R134A on the (replacement) Sanden compressor.

Come to think of it, that's one place I forgot to check for system capacity!  :facepalm:  Thanks for the idea, Brett.

Here is the value of receiving good records when you buy a pre-owned coach:

According to the "Maintenance Book" I got with our coach, on 6/12/2002 at 133,387 miles, 2nd owner Andy Kissinger had the dash A/C converted from R12 to R134.  According to his notes, they used 72 oz. of refrigerant.

Then, on 10/08/2010, 4th owner John K. replaced the dryer, had system flushed, and recharged with "R134 x 6".  I assume that refers to 12 oz. cans, which would also be 72 oz.  John also had the system worked on a couple more times in 2012.  He told me he had put a lot of time and effort into getting the dash air working, which it did when we purchased the coach from him in 2013.

ANYWAY, now at least I have a quantity number to reference when discussing the present problem with a tech.
Chuck, Jeannie & Bella the MalChi
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"It goes without saying..."

Re: Freon Capacity of the A/C system ?

Reply #4
The 34' Forrest takes 5.5 lbs of R143a.  It was painted on the hydraulic reservoir by one of the techs at FOTn when replacing the compressor and drier back in 2003.
Peter & Beth Martin
No Forrest? What have you done?
MC# 15890 until Dec 2016; FMCA #F329677
Cincinnati, OH

Re: Freon Capacity of the A/C system ?

Reply #5
The 34' Forrest takes 5.5 lbs of R134A.
That would be 7.33 cans.  The A/C plumbing could be quite a bit different between Unihome and Unicoach.  Dave M (above) says his 36' U320 takes almost 9 cans!  Wonder what a 45' IH-45 would take?

They sure could simplify these RV dash air systems (on a diesel pusher) if they could mount the compressor up front, and drive it with a electric motor.  Must be possible - don't the Hybrids like Prius use a electric A/C compressor drive?
Chuck, Jeannie & Bella the MalChi
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"It goes without saying..."

Re: Freon Capacity of the A/C system ?

Reply #6
if you search my posts, I listed how much I put in to get what I wanted. The numbers everybody say are just numbers. Hose length, drier type, etc all have effect on amount of refrig required. If you have a txv system, the charge isn't absolutely critical as it tolerates more variation than a fixed orifice system. The idea is to have enough refrig to have pure liquid at the expansion device. Txv are supposed to be fixed superheat, so subcool is they theory. Mine blows super cold and cycles because thermostat in duct cuts it ogg. Ft used small ducts and vent. I need more airflow over evap. The entir plenum sweats
1998 U270 34'

Re: Freon Capacity of the A/C system ?

Reply #7
That would be 7.33 cans.  The A/C plumbing could be quite a bit different between Unihome and Unicoach.  Dave M (above) says his 36' U320 takes almost 9 cans!
This makes perfect sense if you consider the Unihome has only the compressor in the rear so only gas is in the lines between front and back.  The Unicoach has the compressor and the condenser in the rear so one line is liquid, the other gas.  I assume doing away with the front grill on the Unicoach forced FT to put the condenser in the rear.  With the generator and entry steps up front (compared to a Unihome) there must not have been enough room to put in the condenser up front too.
John Fitzgerald
1991 U300 (SAI) Side Asle Island Bed 40'
Detroit 6V92 with Allison Retarder
Meridian (Boise), Idaho



Re: Freon Capacity of the A/C system ?

Reply #10
Not clearly understanding what my ac system is trying to tell me.  Hooked up the gauges,  idled the coach for about 10 minutes.  Opened up the gauge valves with the ambient temperature at 78 F;  Both the hi and low side pressures rread steady at 65psi with the ac blowers on high at the coldest setting.   The compressor clutch is running,  the condenser fan is spinning strong,  the condenser looks clean.  Yet the ac is not blowing very cold at all.   Not sure it's safe to add a can of 134 to see if ac improves.  Suggestions?
Fiddler
1959 Parris Island grad
40' 2001 U320 Build 5875
1999 Suburban K1500 toad
1986 Corvette Pacecar
ssoftail@comcast.net

Re: Freon Capacity of the A/C system ?

Reply #11
Fiddler,
I am sure not an expert on anything, but watching the Tenn RV tech on my unit, having both the hi & lo reading the same is not normal, having my system emptied, the tech knew where he was, so not guessing.
The only time both gauges read the same is when the confessor is not turning / Off.  Could your compressor have an issue ?
I just know mine is doing fine, in fact think the defective switch had been erratic before it quit as now it gets cold.

Re: Freon Capacity of the A/C system ?

Reply #12
Yeah either your orifice is blown out or your compressor does not compress.  Adding refrigerant probably won't help unless you see a pressure differential between the high and low side.  Maybe your compressor clutch is slipping?

Re: Freon Capacity of the A/C system ?

Reply #13
Not clearly understanding what my ac system is trying to tell me.  Hooked up the gauges,  idled the coach for about 10 minutes.  Opened up the gauge valves with the ambient temperature at 78 F;  Both the hi and low side pressures rread steady at 65psi with the ac blowers on high at the coldest setting.  The compressor clutch is running,  the condenser fan is spinning strong,  the condenser looks clean.  Yet the ac is not blowing very cold at all.  Not sure it's safe to add a can of 134 to see if ac improves.  Suggestions?
Don't open the valves on the gauges leave them closed what are your pressure readings with the compresor running?
91 GV U300 Unihome 40' Build 3811
6V92TA Detroit

Re: Freon Capacity of the A/C system ?

Reply #14
Don't open the valves on the gauges leave them closed what are your pressure readings with the compresor running?
I'm ready to try anything, Stump.  Take me thru the sequence of steps on how to get a pressure reading with the valves closed on the gauges.  thx
Fiddler
1959 Parris Island grad
40' 2001 U320 Build 5875
1999 Suburban K1500 toad
1986 Corvette Pacecar
ssoftail@comcast.net

Re: Freon Capacity of the A/C system ?

Reply #15
Ok when you connect your set of manifold gauges not a little recharge set a real manifold set ,with a gage for whatever refrigerant you have in your system. If it's 134a the gauge will say 134a on it etc. the blue one is your low side and the red one is your high side.Close the knobs on the gauges and connect to the RV , The only time you will open a knob is  if and when you need to add refrigerant and then you will only open the low side blue gauge ,Never open the right hand knob on the high side,It can explode a can of refrigerant if you have one connected to the gauges. Now slightly open each hose where it connects to the gauge and let a little refrigerant out this purges the hoses so no air is in them. Ok Now look at your gauges if the compressor is not running both will show the same pressure,the system will be equalized, both on the high and low sides. when the compressor is running the low side should be somewhere in the 40lbs range The high side will be in the 275 up range. The cooling fan will cycle depending on the high side red gauge pressure.it operated off of a pressue switch.  When you look at your gauges you will see scales on it under the PSI numbers these are tempertures. Ok so we start up everything and your compressor is short cycling on and off what is teh pressur reading when it starts,Usually this indicates you have a low charge,add some refrigerant,untill it stays on read your gauges. Now we need to know if you have a TXV system,''expansion'' valve or a capillary tube system ,a expansion valve will be a metal diaphram looking deal with a small line comming off it connected to the suction line ,'' the line that gets cold'' thats the low side line,you probably have a TXV system. But at this point I need to know some pressure readings to take this farther.
 I owned a HVAC company for over 10 years and specialized in system troubleshooting and diagnosis,before making a mid life career change.
91 GV U300 Unihome 40' Build 3811
6V92TA Detroit

Re: Freon Capacity of the A/C system ?

Reply #16
Ok when you connect your set of manifold gauges not a little recharge set a real manifold set ,with a gage for whatever refrigerant you have in your system. If it's 134a the gauge will say 134a on it etc. the blue one is your low side and the red one is your high side.Close the knobs on the gauges and connect to the RV , The only time you will open a knob is  if and when you need to add refrigerant and then you will only open the low side blue gauge ,Never open the right hand knob on the high side,It can explode a can of refrigerant if you have one connected to the gauges. Now slightly open each hose where it connects to the gauge and let a little refrigerant


thx for the reply Stump.   My Gauge set is the real set.  The compressor runs OK yet still no cooling.   Noticed upon removal that the High side fitting was extremely hot to the touch...and the yellow line while looped to itself, upon removal, had some oil in it; is this normal?  I think I will attempt to add refrigerant today and watch the gauges;  if no improvement,  I guess time to let a local ac shop look it over...
Fiddler
1959 Parris Island grad
40' 2001 U320 Build 5875
1999 Suburban K1500 toad
1986 Corvette Pacecar
ssoftail@comcast.net

Re: Freon Capacity of the A/C system ?

Reply #17
What are your gage readings?
91 GV U300 Unihome 40' Build 3811
6V92TA Detroit