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Old 09-27-2021, 10:43 AM   #1
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Dash A/C- Max A/C not as cold as Reg A/C

My 2002 Suncruiser 35U is built on a Workhorse chassis. The Max A/C setting on the dash A/C is not as cold as the regular setting. What should I look for and where?
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Old 09-27-2021, 05:23 PM   #2
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Bob, not to be a smart, er…. Alec, but I would look for a qualified auto/truck A/C tech. Dash A/C is such a specialized subject, and more auto and truck related than RV related that a quick trip to an A/C shop can be the best solution.
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Old 09-27-2021, 05:35 PM   #3
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Quote:
Originally Posted by creativepart View Post
Bob, not to be a smart, erÖ. Alec, but I would look for a qualified auto/truck A/C tech. Dash A/C is such a specialized subject, and more auto and truck related than RV related that a quick trip to an A/C shop can be the best solution.
Funny you should recommend that and no offense taken. I've posted the exact same thing in responding to dash air posts but I was thinking it might be something simple like a vacuum hose or something since the A/C itself works. I also posted on the Workhorse forum on IRV2.
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Old 09-28-2021, 07:41 AM   #4
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I haven't yet pursued them but I've been getting some suggestions on IRV2.com's Workhorse forum. In case anyone is interested, here's the link:

https://www.irv2.com/forums/f22/max-...22-555613.html
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Old 10-10-2021, 06:33 PM   #5
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On the "more mature" chassis like you and I have, the culprit is usually eroded vacuum lines. The Evans Tempcon units were very popular, and many of them used a soy-based hard vacuum tube. Those either weathered away or were consumed by rodents. mine had pretty much dry-rotted. I ran flexible rubber tubing in many stretches where I could, but I still wasn't back to 100%. At first I decided to run an isolation valve to the heater core as a stopgap fix. That interfered with the water heater though. I found that I was getting enough vacuum to close the vacuum motor coolant isolation, but not enough to close the outside air vent. That vacuum motor was easy to get to, so a zip-tie later and it was shut snugly. The air was cooler after that.

Check the operation of your vacuum controls.
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Old 10-10-2021, 09:51 PM   #6
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As DryCreek said - those models tended to have the very tiny vacuum lines just rot away. It happened on our 2005 Adventurer with the W22 Workhorse chassis. I replaced them with silicon vacuum lines from Amazon, but that was only 1/2 the problem.

The other 1/2 were the 2 vacuum actuated controls - one on the hot water line running into the heater core, and the other which snaked done below the entire heater assy (engine side). And that was the bigger problem - because that actuator controlled a flap on the underside of the air intake.

When the dash A/C control is on just A/C that flap is supposed to be open to bring in fresh outside air. When you switch the dash control to Max A/C that flap is supposed to close, thereby re-circulating cabin air - which is supposed to be cooler than hot outside air you may be drawing in.

The problem is - my actuator was totally rusted up - given it's location right in front of the front tire. So even with a replaced vacuum line it would not move the air flap. Took some cleaning and lubing of these parts before I could get the a vacuum to move it. But also found that there is a drain hole right below that was totally clogged with dirt - which caused another problem - freeze up of the A/C core there - particularly on hot humid days. That hole was critical to allow melting ice on the core to drain away. With it clogged the ice layer just grew and soon started shutting down air flow. So cleaning out this drain hole helped remove that problem - though freeze up might still occur sometimes - at which point I could only shut the A/C compressor off by moving the dash knob to just air in - which woulf quickly melt the ice dam.

One other point about Workhorse engine A/C syztems - apparently they made them with old style hoses which were used in old R-12 systems. When they switched to R134 it was discovered that this smaller molecule could bleed right through the old hoses. Very slowly - but after about 6 mths most of the freon would be gone. So we learned to re-charge with R-134 every few months - amazing how cold that unit would get with a proper freon charge. This very likely applies to your rig as well.

Ask a simple question . . .
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Old 10-10-2021, 10:48 PM   #7
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We’re going on a trip next week which will give me a chance to check it out more completly. Thanks for everyone’s suggestions.
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Old 10-11-2021, 09:02 AM   #8
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Air conditioners don't really have some Turbo-boost in them. If the compressor is on, it's on. Then on the other side, a fan is blowing the cool air through the condenser coil, and transferring that cooler air into the cabin. As such, max cool just has a higher fan setting, and the compressor turned on. It's not uncommon that the air from the vents is a little warmer, being diluted by increased air flow. But it could also be that your Freon is a touch low too. This will give you a feeling for typical vent temps, a good hint on Freon levels. https://drivrzone.com/proper-auto-ac-vent-temperature/
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Old 10-11-2021, 01:03 PM   #9
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agree on the hoses.mine rotted out too.one of em had a split in it about 6 inches long,grab the hose and it just crumbled in my hand.
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Old 10-11-2021, 03:55 PM   #10
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One of the suggestions I received on IRV2.com is:

It should be noted that MAX AC only works better than normal AC once the ambient inside air temperature is cooler than the outside air temperature.
Use Normal AC to start, then switch to MAX for the best results.


I'm going to check this out on our trip next week.
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Old 10-11-2021, 05:49 PM   #11
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MAX just recirculates cabin air instead of bringing in outside air. That's why it works better after the cabin is cooler than the outside air, if you use MAX when the cabin has been closed up and is hotter than the outside air you will naturally get warmer air from the vents. MAX does not speed up the fan, it just sounds louder because the door to the cabin opens to let in cabin air and in most vehicles the air flow will increase because it is no longer pressurizing the cabin with outside air, pressure is equal on both sides of the blower. Due to the reduction of static pressure the fan could speed up a bit but it is not an additional speed designed into the system, it is just what a blower does when static pressure is reduced, it moves more air.

It is actually a bit less load on your engine and less heat on your condenser running MAX since it is cooling air that has already been cooled therefore removing less heat to transfer to the condenser. With climate control it also means, on newer systems, that the compressor ON time is reduced.
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