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Topic: Dash A/C  (Read 922 times) previous topic - next topic

Dash A/C

My dash A/C temp is not what I think it should.  I have replaced the cycling switch, expansion valve, receiver dryer, refrigerant, oil and completely flushed the system.  The A/C technician measured air temp out of the drivers vent at 47 degrees when the compressor was on and 53 degrees when the compressor cycled off.  The out side air temp was 63 degrees.  Is it normal for the A/C to cycle on and off every minute or so.  There is no A/C thermostat to adjust the air temp that I have found on the coach.  My question is my A/C preforming normal ? The cycling seems excessive to me.
Terry
Terry and Cheryl Brown
1997 U295 36'
Build #5066
2006 Jeep TJ Rubicon
1993 BMW R100 GSPD

Re: Dash A/C

Reply #1 –
Were the condenser fans on?  If not, high side pressure could reach extremely high level and on many systems cycle off the compressor.
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: Dash A/C

Reply #2 –
Are you sure there is enough 134 in there?  Could be low pressure switch cutting out.
Rick & Rhonda
2003 U320 4220  Build #6199
Was
91 36' GV 300 Caterpillar, 92 40' U280 300 Cummins, 97 36' U295 300 Cummins, 2002
U320 450 Cummins
(Guess we're hooked)

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Re: Dash A/C

Reply #3 –
I am wondering how cold you think it should be with the 63f outside ?
My coach in the 75 f days gets into the upper 40's also as long as the condenser fan works.
Just wondering, as I am NOT an a/c tech.
Dave M

Re: Dash A/C

Reply #4 –
Quote from: wolfe10 –
Were the condenser fans on?  If not, high side pressure could reach extremely high level and on many systems cycle off the compressor.

The condenser fan comes on when the compressor is running.  What else could be the problem?
Terry and Cheryl Brown
1997 U295 36'
Build #5066
2006 Jeep TJ Rubicon
1993 BMW R100 GSPD

Re: Dash A/C

Reply #5 –
How are the pressures reading?
Rick & Rhonda
2003 U320 4220  Build #6199
Was
91 36' GV 300 Caterpillar, 92 40' U280 300 Cummins, 97 36' U295 300 Cummins, 2002
U320 450 Cummins
(Guess we're hooked)

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Re: Dash A/C

Reply #6 –
 Does the dash AC system have a orifice tube and expansion valve?  The low pressure drops to the compressor shuts off.  The high side is within limits.  If there is a orfice tube that is clogged could that cause my problem?
Terry
Terry and Cheryl Brown
1997 U295 36'
Build #5066
2006 Jeep TJ Rubicon
1993 BMW R100 GSPD

Re: Dash A/C

Reply #7 –
I wonder if its just not fully charged.
Rick & Rhonda
2003 U320 4220  Build #6199
Was
91 36' GV 300 Caterpillar, 92 40' U280 300 Cummins, 97 36' U295 300 Cummins, 2002
U320 450 Cummins
(Guess we're hooked)

The selected media item is not currently available.

Re: Dash A/C

Reply #8 –
Terry- I don't know about FT systems [so perhaps I shouldn't post] but I could share some automotive A/C experience with you:  Sometimes when all the pressures look good and there is every reason to believe the AC system is strong enough; e.g., the compressor high side is warm/hot to the touch, the suction side is iced-tea-glass cold .... one should (contrary to English Jurisprudence) assume the air temperature control elements are defective/guilty until proven innocent.  In older vehicles, the outlet air temp to the passengers was controlled by a valve which throttled hot water through the heater core.  Hot water leaking leaking through that valve into the heater core could knock even the strongest A/C for a loop...hot water won every time.    On newer cars/pickups (a '97 would be newer, IMHO) a vacuum-controlled door mixes hot air from the heater core in with the cold air from your A/C evaporator to accomplish air temperature control.  A defective vacuum "door actuator" caused a problem like yours on my '09 Yukon last summer. It was in the shop for 2 days because it was intermittent......glad I had extended warranty + I am too old to crawl under dashes anymore.  I would wager FT systems are just like other automotive systems; i.e., when "on" the A/C "goes for broke" with the expansion valve (or orifice tube) keeping the evaporator just above freezing (as sensed by the cut-off [pressure sensing] switch) ...... and to control air outlet temp, heat is added as needed.  Your AC tech knows all this stuff about the air mixing valves...... but you might run it by him, anyway.  Good luck.....know this can be exasperating.  Ed (no FT.... yet) Sievers.

ps While composing this note, I noted your later post.  Since you have a TX valve, you should not have an orifice tube.  The orifice tube systems do have a filter screen which is integral with the tube.  They will sometimes clog (with residue from an older filter/dryer) but that causes rapid cycling......every few seconds if the compressor is strong (sure, they compress, but they suck like crazy too.....which we often forget ;D ).  If the frustration level gets to ya, PM me and I will give you a call....and save all these good forum members from my "ramblings".
Ed Sievers
"Be the person you needed when you were younger"

Re: Dash A/C

Reply #9 –
Quote from: Johnstons –
I wonder if its just not fully charged.

Good question.  The AC tech put 5 lb in after he changed out the parts.  He wants me to wait till the weather warms up to the 70's, then check the system again.  I don't understand what outside temps have to do with the compressor cycling but I am game.  More to follow.
Terry
Terry and Cheryl Brown
1997 U295 36'
Build #5066
2006 Jeep TJ Rubicon
1993 BMW R100 GSPD

Re: Dash A/C

Reply #10 –
My money is on needing several more cans of referigerant.
Rick & Rhonda
2003 U320 4220  Build #6199
Was
91 36' GV 300 Caterpillar, 92 40' U280 300 Cummins, 97 36' U295 300 Cummins, 2002
U320 450 Cummins
(Guess we're hooked)

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Re: Dash A/C

Reply #11 –
Quote from: Johnstons –
My money is on needing several more cans of refrigerant.

Rick,
I sure hope you are right.  I should find out soon.
Terry
Terry and Cheryl Brown
1997 U295 36'
Build #5066
2006 Jeep TJ Rubicon
1993 BMW R100 GSPD

Re: Dash A/C

Reply #12 –
It would be helpful to see what the guage readings are while it is operating. If as you said the low side guage goes very low then the low pressure switch would shut off the compressor, which would indicate a restriction to me. Possible partial blockage of the expansion valve. Of course the thermostat could be bad as it has a probe into the evaporator core.
previous 1984 35 ft ORED 250 HP 3208 Cat       
previous 1998 40 ft U295 CAI 325 hp Cummins
previous 2003 40 Ft u320 build #6140 450 Cummins M11.                                                         
1999 Mazda Miata
Ron, Nancy, Tipper the cat, Max The dog
1997 U 270 36 ft build number 5174 8.3 Cummins

Re: Dash A/C

Reply #13 –
If there isn't adequate freon it would be pumping it all to the high side and starving the low side thus setting off the low pressure cut off. I bet that's all it needed in the first place.
Rick & Rhonda
2003 U320 4220  Build #6199
Was
91 36' GV 300 Caterpillar, 92 40' U280 300 Cummins, 97 36' U295 300 Cummins, 2002
U320 450 Cummins
(Guess we're hooked)

The selected media item is not currently available.

Re: Dash A/C

Reply #14 –
Quote from: red tractor –
It would be helpful to see what the guage readings are while it is operating. If as you said the low side guage goes very low then the low pressure switch would shut off the compressor, which would indicate a restriction to me. Possible partial blockage of the expansion valve. Of course the thermostat could be bad as it has a probe into the evaporator core.

How do you check the thermostat?
Terry and Cheryl Brown
1997 U295 36'
Build #5066
2006 Jeep TJ Rubicon
1993 BMW R100 GSPD

Re: Dash A/C

Reply #15 –
You can check if it is causing the 12 volts to stop coming from it when the compressor stops or if it is still allowing the 12 volts to flow. If it has 12 volts on both terminals and the compressor shuts off you know that is not the cause of the shut down. The thermostat is under the dash.
previous 1984 35 ft ORED 250 HP 3208 Cat       
previous 1998 40 ft U295 CAI 325 hp Cummins
previous 2003 40 Ft u320 build #6140 450 Cummins M11.                                                         
1999 Mazda Miata
Ron, Nancy, Tipper the cat, Max The dog
1997 U 270 36 ft build number 5174 8.3 Cummins

Re: Dash A/C

Reply #16 –
Quote from: red tractor –
You can check if it is causing the 12 volts to stop coming from it when the compressor stops or if it is still allowing the 12 volts to flow. If it has 12 volts on both terminals and the compressor shuts off you know that is not the cause of the shut down. The thermostat is under the dash.

Thanks, I'll check it.
Terry
Terry and Cheryl Brown
1997 U295 36'
Build #5066
2006 Jeep TJ Rubicon
1993 BMW R100 GSPD

Re: Dash A/C

Reply #17 –
Some of the things that can make an air conditioner less efficient can be something as simple as dirt on the condenser or evaporator fins.  It is also important to have the correct amount of oil and refrigerant in the system.  Too much refrigerant effectively reduces the size of the condenser as liquid refrigerant will fill up the lower portion of the condenser.  Oil to some extent will circulate through the system.  Too much will coat the inside of the tubing in the condenser and evaporator reducing heat transfer. It can also collect in the dryer reducing refrigerant flow.  Not enough oil and the compressor wears out faster than it should.  One should not add oil just to be on the safe side, only when it is known that oil has been lost like replacement of a major part. Of course the system should be properly evacuated before refrigerant is added.  The condenser on my coach did not have a shroud for the fan.  Air was just basically being pulled through the center section of the condenser.  If you can work with sheet metal it is not difficult to make a shroud that positions the fan a little farther away (an inch or two) from the condenser and pulls air through all of the condenser.  Just be careful not to puncture any of the tubing with a drill or screw.  The box around the evaporator at the dash has doors to direct air flow, both inside and air from outside.  These doors can be operated by electric motors, vacuum motors, manually, and by other means.  They should be working properly and not stuck in a position that lets outside air in.  And as mentioned the heater should not have hot water flowing through it.  My coach has a switch for fresh air, blend, and inside air; however the door for that is either open or closed there is no blend position.  With blend selected the door could be either open or closed.  Other coaches may be different and work correctly.  Most of the time when the compressor cycles on and off it is usually low on refrigerant, but could be other things like a defective switch.  There should be a sight glass on the receiver/dryer located near the condenser on the liquid side.  There should be no bubbles in view after the system has been operating continuously for about 10 minutes and not cycling on and off.  You may need a mirror to view the sight glass on top of the receiver/dryer.  I'm not a refrigeration guy, just things picked up over the years.   
Jerry Whiteaker former owner 96 U270  36' #4831 Austin,TX-Owner Mods LCD TV w/front cabinet rebuild - LCD TV bedroom - Dual Central AC, either can cool coach w 30 amp - Skylights at roof AC openings - Drop ceiling for ducting of AC - Shower skylight white gelcoat/wood/epoxy frame - Air Springs/Shocks replaced - 2014 CRV - 8K Home Solar - Chevy Volt

Re: Dash A/C

Reply #18 –
Quote from: Jerry Whiteaker –
Some of the things that can make an air conditioner less efficient can be something as simple as dirt on the condenser or evaporator fins.  It is also important to have the correct amount of oil and refrigerant in the system.  Too much refrigerant effectively reduces the size of the condenser as liquid refrigerant will fill up the lower portion of the condenser.  Oil to some extent will circulate through the system.  Too much will coat the inside of the tubing in the condenser and evaporator reducing heat transfer. It can also collect in the dryer reducing refrigerant flow.  Not enough oil and the compressor wears out faster than it should.  One should not add oil just to be on the safe side, only when it is known that oil has been lost like replacement of a major part. Of course the system should be properly evacuated before refrigerant is added.  The condenser on my coach did not have a shroud for the fan.  Air was just basically being pulled through the center section of the condenser.  If you can work with sheet metal it is not difficult to make a shroud that positions the fan a little farther away (an inch or two) from the condenser and pulls air through all of the condenser.  Just be careful not to puncture any of the tubing with a drill or screw.  The box around the evaporator at the dash has doors to direct air flow, both inside and air from outside.  These doors can be operated by electric motors, vacuum motors, manually, and by other means.  They should be working properly and not stuck in a position that lets outside air in.  And as mentioned the heater should not have hot water flowing through it.  My coach has a switch for fresh air, blend, and inside air; however the door for that is either open or closed there is no blend position.  With blend selected the door could be either open or closed.  Other coaches may be different and work correctly.  Most of the time when the compressor cycles on and off it is usually low on refrigerant, but could be other things like a defective switch.  There should be a sight glass on the receiver/dryer located near the condenser on the liquid side.  There should be no bubbles in view after the system has been operating continuously for about 10 minutes and not cycling on and off.   You may need a mirror to view the sight glass on top of the receiver/dryer.  I'm not a refrigeration guy, just things picked up over the years. 

It would be great if the compressor would run 10 minutes before it cycles off. It only runs 40 seconds the cycles off for 60 seconds the cycles back on. 
Terry
Terry and Cheryl Brown
1997 U295 36'
Build #5066
2006 Jeep TJ Rubicon
1993 BMW R100 GSPD