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Old 05-03-2021, 05:24 PM   #1
Winnebago Owner
GTobey's Avatar
Join Date: Aug 2016
Posts: 69
Forza Dash A/C works for a while, then doesn't

2016 Forza 36G. Have had this issue since new. Drive for an hour or so, running dash A/C on recirculate with fan on high or one below high. Will cool for an hour or so, then air flow through vents slows down, not cool, but not warm. When stopped after running like that, water would drain out of condensate drain hose for another hour.

Have had this system checked by 3 different shops, including Freightliner in Gaffney, SC, and all pressures in specs, cooling temps proper, but they don't drive it for an hour, just long enough to test it.

Just got back from Winnebago in Forest City, IA, where they checked everything including cleaning condensate drain tube for a blockage, "they said". At least that's what I was charged for. They state all cooling was according to specs, of course! Again, they did not drive it for an hour.

So, on my way home, I said the heck with it. Just run the A/C and see what gives. And on my way home to VA from IA, when I stopped to get fuel a couple of times after having the A/C on, I would witness a curved piece of ice fall onto the pavement under the front of the coach, just in front of where the genset is. The bit of ice was molded in the shape of a crimped metal sleeve which is around the evaporator hose. I opened the hood, and this is what I found in the pictures attached.

Went into a restaurant to eat, an hour later, the condensate drain was still dripping. So back to square one, several thousand miles later, several hundred gallons of fuel burned, rubber off the tires, and on and on, with the same issue I left home with!

So what is next? Anyone experience the same issue?
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Old 05-03-2021, 05:45 PM   #2
Winnebago Master
Join Date: Nov 2018
Location: Pflugerville/Austin, Tx
Posts: 3,029
AC is working too well! It is freezing up after long term use.
One thing that might do this is a lack of good airflow around the cooling coil unit inside.
One might need to do a check of the venting for any form of blockage. That is what causes the airflow to slow and nearly stop as the coils get more and more frozen into a block of ice.
One way to avoid this might be to just switch to outside air occasionally rather than running the inside air around again on recirculate.
More likely to happen on somewhat warm, not terribly hot day when humidity is high.
If there is some form of blockage like from the wife getting cold and closing her vents while you are hot and trying to get more cold air, I find it more likely to freeze up.
2015 Winnebago Vista 31KE on 2014 chassis
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Old 05-03-2021, 08:04 PM   #3
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Join Date: Oct 2018
Location: Kingsland, Texas
Posts: 94
Seems like a bad sensor / pressure switch somewhere, preventing the AC compressor from cycling. In cars there is a sensor switch that prevents the compressor from running non-stop - otherwise it freezes up like you are experiencing. Testing it does NOT involve checking vent output temperature....
2018 Vista LX 27N
2015 Jeep Rubicon and ATC Open Car Hauler
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Old 05-03-2021, 10:25 PM   #4
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Join Date: Jul 2014
Posts: 925
Now that you have a symptom to go on, the experts will know what to do better than me.

If I were to guess, I would say your thermostat with a metal wire/probe that monitors the freezing of your evaporator IS doing it's job and shutting down your system like it should

WHY is this happening is the question?

* Sounds like the compressor is always running; and if refrigerant flows, then the system will keep cooling, which is good.

However, if you don't have enough volume of air passing over and threw those evaporator fins it will freeze, and that is what you are telling us.

==> All your binary switches are Normally Closed (NC) and open when there is a problem. So you are dealing with poor air flow or a bad TXV... IMO.

Here is what I found by googling: What causes the evaporator to freeze in an RV?

==> Do you have an air filter that is clogged? ...My coach did not come with one, but maybe your newer RV does?

* My guess is that you have a bad expansion valve (TXV), but before you open up your "closed AC system," you might look at these easy to troubleshoot items:

* Have you go a Bosch Relay mounted on your firewall above your generator? ...If so test it. I.e., pins 85-86 are the coil voltages and you should have "continuity" between them.

If you don't know how to test a relay then just buy a new one for $10-$15 at any auto parts store and see if that fixes your problem? If not, it's always good to have a spare relay.

* Maybe your temperature control board (behind your 3-knobs) is causing you trouble? (See picture below.) Are you getting full fan speed?

* If still no luck, turn up your air temperature so you blend door is not 100% recycling cool air.

Note: Most people have the opposite problem. I.e., they can't get there AC cold enough. So consider yourself lucky... that your thermostat is shutting down your compressor.

Question: When your evaporator was freezing over, was it humid outside?

* Final comment: If you do replace your TXV you should also replace your Receiver-Air-Dryer. These things are cheap and easy to replace; and you can use any type. Mine took an AC-Delco Receiver-Air-Dryer... and FYI Winnie installed a Ford/Sanden Compressor. So don't be surprised if you find second source parts from the automotive industry that predate your RV by more than 5 years! ...My Mercedes TXV was used back in 1998 and I drive a 2004 Itasca Horizon 40AD.

* Your 134A weight is also placard on the back of your firewall. However, you can add 10% more and this is a good idea IMO. However, some "stuffy" AC mechanics will not put in more that what is called for. So just tell them what you want and maybe they will not see the placard.
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