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Old 06-27-2014, 02:20 PM   #1
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ACME Dash AC help

Have a 2002 Tiffin Allegro bus and the dash AC stopped blowing cold recently. I tried to charge it up but getting strange readings on the charge gauge. When I first begin to charge the system at the low pressure line fitting I get a reading showing the pressure is a little low. But then after a few minutes I get no reading at all. When the line is connected and the AC and engine are off I get a reading. Haven't been able to tell if the compressor is engaging or not. It's almost impossible to see with the engine running. The only access is through the bedroom floor hatch and I certainly don't want to run the engine with that open. Looking for help on trouble shooting.

Thanks.

JC
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Old 06-27-2014, 03:05 PM   #2
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It could be that the pressure is low enough that the low pressure switch has shut off the compressor clutch. You really need a full manifold gauge set to read high and low pressures to properly charge the system. If it's low enough to shut off the LP switch, you probably have a severe enough leak it needs to be found and fixed.

You can run engine with the floor hatch raised, just don't drive it. You could also put a jumper wire from a known 12v (+) to the compressor clutch wire, but if there's no fluid, it's not a good idea.
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Old 06-27-2014, 04:00 PM   #3
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My guess is low gas....

You see some pressure then it goes away.

When compressor not running all of system at same pressure from coolant.

When compressor runs it draws down low side.

If it is too low it will cycle due to low pressure safety switch which should never be bypassed by non pro folks.
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Old 06-28-2014, 08:31 AM   #4
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That sounds like a logical approach. Any idea how much coolant these systems hold?
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Old 06-28-2014, 08:48 AM   #5
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ACME Dash AC help

I would take it to a pro. They have the right gauges to put the correct amount of freon in and also they can check for any leaks.
It does sound like it is low.
As for how much it holds, there may be a sticker somewhere in the engine compartment that will tell you how much it holds if it is empty.
You can try adding a pound and a half to see if that corrects the problem. Maybe even two pounds but that may only start the system working but not to full capacity. Some older A/C systems do not have a high pressure switch to turn off the a/c which would allow you to add too much freon and damage the system.
Being a 2002 model maybe the system has a very very slow leak and it just hit the low end to turn off the system. Adding a pound or two may not hurt it then. But not any more.
But like I wrote it is best to take it to a pro. Well worth the money if you can find one that is reasonable.
I have been using the same auto a/c pro for over 40 years that only charges $60 to put freon in it and check for leaks.
Good luck.


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Old 06-29-2014, 09:09 AM   #6
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You should have a light on the dash that shows when the compressor is on, the light will be lit. Look close if your dash air is like mine, it's a little led on one of the buttons. Also if like mine, the compressor clutch wasn't engaging, I had a schematic of the wiring sent to me and it shows a 10amp fuse in the wiring behind the dash that controls the compressor clutch. Mine was blown, (probably as a safety feature when the 134a was lost), replaced the fuse and hey, hey, hey the compressor now engages and the little green led comes on. I don't have the schematic PDF on this computer, its at home and we are in branson, but if you search the internet for your type of AC, you might find it. Also search this forum cause I think I may have posted it here somewhere under AC problems.
Hope this helps
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Old 06-29-2014, 10:54 AM   #7
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Quote:
Originally Posted by Chaffeekid View Post
You should have a light on the dash that shows when the compressor is on, the light will be lit. Look close if your dash air is like mine, it's a little led on one of the buttons. Also if like mine, the compressor clutch wasn't engaging, I had a schematic of the wiring sent to me and it shows a 10amp fuse in the wiring behind the dash that controls the compressor clutch. Mine was blown, (probably as a safety feature when the 134a was lost), replaced the fuse and hey, hey, hey the compressor now engages and the little green led comes on. I don't have the schematic PDF on this computer, its at home and we are in branson, but if you search the internet for your type of AC, you might find it. Also search this forum cause I think I may have posted it here somewhere under AC problems.
Hope this helps
Jim
The dash LED is to show A/C on. There is no light that shows compressor clutch is actually engaged, unless it's been added by owner. The fuse is not a safety feature for low R-134a, but to protect wires in that circuit. There is a low pressure cutoff that shuts off power to the compressor clutch when pressure drops below acceptable pressure, nothing else.
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Old 06-29-2014, 11:51 AM   #8
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Well BFlinn181, the light was not on, the clutch was not engaged, replaced the fuse, light is on clutch engages when the button is pushed and the clutch engages and the AC COMES ON. So what is the light for, shows the AC Compressor is running, shows the clutch is engaged, pull the fuse the clutch will not engage. Want to tell me again. It is a FACTORY installed light, not an add on.
The fuse protects the Compressor by blowing the fuse when the low pressure fault occurs.
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Old 07-02-2014, 02:10 PM   #9
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Took some readings with the A/C Gauge Manifold Set.
1st image is static pressure with engine off.
2nd is with A/C running.

Thoughts?
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Old 07-02-2014, 02:24 PM   #10
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Quote:
Originally Posted by Chaffeekid View Post
Well BFlinn181, the light was not on, the clutch was not engaged, replaced the fuse, light is on clutch engages when the button is pushed and the clutch engages and the AC COMES ON. So what is the light for, shows the AC Compressor is running, shows the clutch is engaged, pull the fuse the clutch will not engage. Want to tell me again. It is a FACTORY installed light, not an add on.
The fuse protects the Compressor by blowing the fuse when the low pressure fault occurs.
If you turn the temperature control UP on the dash control, the temperature should cause compressor clutch to turn off. I think the light on the HVAC dash control will still be lit because the A/C is ON but not calling for the compressor.

Quote:
Originally Posted by gatorcruz View Post
Took some readings with the A/C Gauge Manifold Set.
1st image is static pressure with engine off.
2nd is with A/C running.

Thoughts?
At what temperature? if you Google 'R-134 pressure chart' you'll find that your readings must be considered against the ambient temperature.
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Old 07-02-2014, 03:52 PM   #11
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It looks low, but you may also have a restriction somewhere causing it to pump down like that.
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Old 07-02-2014, 05:01 PM   #12
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Whiskey, that was my thinking as well with the negative pressure reading on the low side... question is WHERE? expansion valve??? evaporator?
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Old 07-02-2014, 07:01 PM   #13
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From the reading on the gauges while running the compressor, I'd say that the expansion valve is stuck closed. While it is running, is one side if the expansion valve cold? BTW, I am not an A/C tech. Know just enough to be scary
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Old 07-02-2014, 08:52 PM   #14
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The restriction is more than likely in the metering device (ie TXV or Orfice). You would need to change it, and the accumulator/Dryer and recharge with gas. Might want to put a little UV dye in the system to check for leaks in the future.
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