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Old 08-18-2022, 11:24 AM   #1
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How to clean AC evaporator Core

Hello all. Im new to the site so if Im posting in the wrong place; my apologies.

I have a 2007 40 Holiday Rambler Endeavour.

The engine AC works intermittently (cutting out on low pressure S/W.) The gas is full (52 oz).

The high pressure side is too high and the low pressure side is too low.

Added more gas till site gauge was clear (7oz more).

This keeps it running but the pressures are still way off. Weve concluded theres not enough load across the evaporator.

Has anyone figured out a way to get in and clean the core??? Need more airflow through it!!!

Thanks for any advice.

Mike
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Old 08-18-2022, 12:23 PM   #2
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You don’t charge R134 units to a clear site glass - your probably overcharged.

Are you sure it’s cutting out on the low pressure switch? Generally there are also high pressure cut-out switches, and then you may have an evaporator thermostat.
Whose air box is in you coach? Evans? SCS? Evans-Tempcon? Other?

It is more likely an expansion valve issue.

Post a picture or two of your air box - and if you know suction/discharge pressures, ambient outside temperature, and coach interior temperature at the air inlet (typically under the dashboard) then we might can help you more.

I know on our current and past coaches, the newer one being 20 years old, are not that loaded up. But if you don’t know if a PO of the coach might have had a cat that like to live near the return air to the unit then deeper inspection of the evaporator might be warranted.
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Old 08-18-2022, 12:24 PM   #3
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Sure it’s not an Expansion valve stuck closed or orifice tube plugged?
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Old 08-18-2022, 07:50 PM   #4
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I do remember seeing a notice about not charging to clear the sight glass. I'll reclaim the 7 Oz to get back to factory charge. You're correct, the pressure switch is on the high side
and is cycling the compressor off at around 180+ psig. We washed out the condenser but did not bring down the head pressure. The condenser fan doesn't move enough air across the the condenser with the rig stationary.
In fact the fan motor shroud doesn't cover the complete condenser coil. How does this differ when the rig is moving. Does more air travel across the coil? Back to the low suction pressure ie. 23 psig. I'm getting 8-10 F superheated so the valve is good. Doesn't seem to matter if it's bringing in fresh air or recirculating to air. It seems to be one evaporator coil that the air feeding comes from
outside or inside the rig. However these are 2 completely separate return air ducting.
So the evap is only 50% active thus the reason for such low evap pressure. 50% of the evap has no air across it. Don't know enough about m/h evap ducting to compare.
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Old 08-18-2022, 08:24 PM   #5
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Well, throw out most of what you know about proper evaporator design and airflow when it comes to MoHo’s - at least that has been my experience (although I haven’t worked on a coach over $100,000).

After recent issues with our ‘02 coach, I figured out they put the expansion valve in backwards - they had liquid feeding the top of the coil, and suction out the bottom. Assuming the times the TEV wasn’t stuck, it hunted all over the place.

After much digging and research - I took the unneeded king valve out, rebuilt the suction hose fitting to the TEV to remove the combo function of the king valve, replaced the TEV to feed liquid into the bottom of the coil and suction out the top (as best as I could tell).
Charged the system - TEV barely moves around.
I’m still playing with the charge. The charts say 1.75 #’s unless the chassis has an “auxiliary condenser”, and then it’s 2.75#’s. Still trying to figure out if an “auxiliary condenser” is just a bigger condenser or what. I need to strap a thermometer onto the discharge line and look at superheat.

Are you a single fan or dual fans on the condenser? Do they or it cycle as needed?

What ambient temperature are you running your tests in? High side could go as high as 325psi at 110 degree ambient. There are charging charts that will give you a general idea of what high side pressures should be - assuming everything was sized correctly to begin with.

Automotive A/C units were designed to be moving down the road, so yes, the coach moving is important. But a properly sized condenser and properly operating condenser fans should allow driveway charging.
We used to run water over the condenser when driveway charging back when coil sizing was more of an art than science.

You might go to the Files section of this board under Chassis and search for Evans. There should be a single link to come up that will give you some good info how these systems work.

But if your compressor is cycling on head pressure at 180 psi, I’m thinking you need a new high side pressure switch.
Either that, or the low side pressure switch, or the evaporator thermostat (on some air boxes) is cycling the compressor.

BTW - I trust you have the A/C controls set to “Max” cool and the fan on high.
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Old 08-18-2022, 08:28 PM   #6
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I do remember seeing a notice about not charging to clear the sight glass. I'll reclaim the 7 Oz to get back to factory charge. You're correct, the pressure switch is on the high side
and is cycling the compressor off at around 180+ psig. We washed out the condenser but did not bring down the head pressure. The condenser fan doesn't move enough air across the the condenser with the rig stationary.
In fact the fan motor shroud doesn't cover the complete condenser coil. How does this differ when the rig is moving. Does more air travel across the coil? Back to the low suction pressure ie. 23 psig. I'm getting 8-10 F superheated so the valve is good. Doesn't seem to matter if it's bringing in fresh air or recirculating to air. It seems to be one evaporator coil that the air feeding comes from
outside or inside the rig. However these are 2 completely separate return air ducting.
So the evap is only 50% active thus the reason for such low evap press. Only 50% of the coil is getting return air across.
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Old 08-19-2022, 09:10 AM   #7
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Thanks. You're right, throw any logic out the window. On a 90 F day we're running close to 200 psig with tells me we have a 40 F TD on the condenser. That's high. But standing still there is not enough across the condenser especially with the fan shroud not covering 100% of the coil. Horrible design. Now I'm convinced it may be cycling on low pressure at 20psi suction. Which can be normal on auto a/c application. I'll search for a LPC to be sure.
Engineering not the best
I'll try the water over the condenser to verify
Thanks again
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Old 08-19-2022, 09:27 AM   #8
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Great opinion above.. but just to throw this opinion out.. critters love old rv.. they will eat, nest, and short rv wires.. critters love to nest inside hvac box.. you need to remove blower motor and check box for nest.. you need to inspect evap. .. you could find trash.. or dead animals in box or ductwork.. you need to inspect blower motor.. just saying..
When things go haywire and don't make sense.. keep critters in the back of your mind all the time
Good luck and keep us posted
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