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Old 07-02-2013, 01:30 PM   #1
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Chassis A/C how much freon ?

Any A/C guys out there. 2001 Daybreak / Workhorse. Dash A/C is about 80* with ambient about 90*. I just had it charged but no way to know how much R134a to put in. He recovered 3/4 lb and it has 1.5 lb now. When he put in 2 lb pressures went up and temperature went up also. Compressor seems to cycle fine. Low pressure line at the evaporator is cold but not real cold. Some condensation from the evaporator at times. Low pressure 40-50 and high pressure 275. Heater control valve works OK. I pinched off a heater hose just to be sure. Dash vents seem to change over fine. I am running it on Max-air. We washed out the condenser. Electric cooling fans are running.
Any ideas.
Thanks, Tom
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Old 07-02-2013, 01:33 PM   #2
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I think your high pressure is to high, you want to change your air dryer.
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Old 07-02-2013, 02:03 PM   #3
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Tom, high side is fine with a 90 degree ambient temp

tell me more about your system if you know...is it an expansion valve or orifice tube system?

System was not totally out of freon prior to your bud working on it?

Has anyone ever put "sealer" in the system to try and stop leaks?

If you'd put a garden hose on condenser with the AC "on" will the pressures drop and vent temp get colder?
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Old 07-02-2013, 02:28 PM   #4
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You may have overcharged your system, I always go by the low side, usually around 30#. I would suggest bleeding some off and lower your low side pressure.
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Old 07-02-2013, 03:21 PM   #5
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I think it is an orifice tube. It has a receiver drier with a sight glass, which is cloudy. I don't know about sealer. It has had from 3/4 lb to 2 lbs of Freon and seems to act about the same. When he went from 1.5 to 2 lbs the temp. and pressures went up. Recovered it down to 1.25 lbs and the pressures came back down. We cooled the condenser with air and then water. Didn't help. The guy working on it is an A/C guy at a shop. He kinda gave up. Thinks it is a restriction on the high side. If I knew how much Freon it is supposed to have, it would be a better place to start. Three of us looked for some information and struck out.
Thanks for the input guys.
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Old 07-02-2013, 03:38 PM   #6
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90 is a big heat load especially if its humid. I live in Tucson and expect about 10 degree drop from the intake to the output in the huge area of a Mh. If you can set the guages inside and drive it around a little you might find it pretty close to charged. If it cycles with a hot interior its either shutting off on over high pressure or under low pressure.
Good luck
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Old 07-02-2013, 03:43 PM   #7
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Wow. Maybe a motorhome thing. My pickup, sitting right next to the MH was 51* at the center vent. I would love 60*. I understand the hotter the input, the hotter the output. Compared to any other vehicle I have had, this just isn't right.
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Old 07-02-2013, 09:39 PM   #8
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Every motorhome I have seen uses an expansion valve system. The air conditioning is 1/2 chassis builder and 1/2 body builder. I would be leaning towards an expansion valve issue. It is mounted to the evaporator box. Both lines are attached to it. If there was a restriction in the high side, the low side usually is very low do to the blockage. The evaporator/dryer could be an issue also.

I have found that failed expansion valves are mostly an informed guess. There are better guys out there for A/C diag but this have been my typical diagnosis in the past. I just replaced one on a rear A/C system in a van. Same issues.
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Old 07-02-2013, 10:29 PM   #9
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Don't know if you have seen this but itís discussed here as far as the amount.

How much freon do i put in?
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Old 07-02-2013, 10:37 PM   #10
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Tom, having only used Robinair recovery machines....I'm curious as to how you know what amount of refrigerant has been left in the system upon recovering some of the charge.

Is there any reason to think air has been left in the system?

On a r134a system the sight glass is useless...so don't even waste your time looking at it.

if it is an orifice tube system....it will have a tall aluminum container on the suction(outlet) side of the evaporator.

If it is an orifice tube system, it will use a low pressure switch to cycle the compressor on and off. You say the compressor is cycling fine....typically the compressor will cycle off at 22-25psi low side pressure on an orifice tube system
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Old 07-02-2013, 10:52 PM   #11
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Someplace I have a chart from Evans-Tempcon for the units they make. It lists the amount of "freon" for each unit. On our DSDP it's around 4.0 to 4.5#'s depending on the condenser size.
Ours quit working a few years ago. The compressor doesn't come on so it's probably low on "freon" and I haven't bothered to have it checked.
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Old 07-02-2013, 11:06 PM   #12
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Quote:
Originally Posted by tompen View Post
Wow. Maybe a motorhome thing. My pickup, sitting right next to the MH was 51* at the center vent. I would love 60*. I understand the hotter the input, the hotter the output. Compared to any other vehicle I have had, this just isn't right.
I recently saw a chart (now i can't find it) that said for 90-95 ambient (meaning the temp at the inlet) the output should be 70-72 F. for a MAX. I believe this assumes the dash ductwork is at approximately the same inlet temp (as opposed to sitting in the sun for 4 hours with no A/C running).
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Old 07-03-2013, 08:25 AM   #13
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Quote:
Originally Posted by FTInMyDreams View Post
Don't know if you have seen this but itís discussed here as far as the amount.

How much freon do i put in?
Thanks, my search didn't get me there. Some good stuff.
Bruce. Just tried the comparison again. 75* ambient, Daybreak 61* output, GMC 42* output.
I am just not used to figuring out things that are partially broken. Not a fair comparison with the truck. I admit. Well, I have spent about $100.00 so far and am right where I started. In fairness, the A/C guy didn't charge me, even after 2 hours, recover, evacuate, recharge and scratch head. Not fair. I gave him $50.00 which is still 1/3 of what I expected to pay for the same knowledge.

Don't want to hi-jack my own thread. I will continue to talk to people and think this through until I can convince myself what parts to throw at it. We will be in Florida 2-3 months next winter and their are at least 3 RV A/C shops where we stay.

Thanks All.
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Old 07-04-2013, 08:50 PM   #14
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If your system truly is an orifice controlled A/C check the flow. With a manifold gauge set connected run the system for about five minutes. Make sure pressure is up on the high side. Shut off the compressor and watch the pressures, high and low sides. Pressure should equalize in about 2-3 minutes max. If not replace the orifice tube. I would recommend using a GM variable orifice. It will help with low engine speed cooling and is easier on the compressor when it is cycling.
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