Frustrating dash A/C problem!

hondo12 · 06-17-2015, 05:58 PM

Hello, 2008 Winnebago 38 T class A dash A/C either works or doesnt! took it to a A/C repair garage becuse my A?C was workong partialy or not at all, and to my surprize it worked perfectly on the way there I figured since I had changed the vaccum heater control valve that may have fixed the the problem, got a call from the guy and he confirmed that everything is working right and ajusted the freon just a small amount, Well on the way home no cold air, called the mechanic told him, and he had me feel the freon pipes and hoses and they were totaly warm he than said it must be an electrical problem and bring it back in ,,,,, My question is does anyone know of any reason the coach would shout down the A/C for a saftey or machanical reason?kinda like low on coolant or ? kinda like the way the generator shuts down with a low fuel in the tank. Anyone know of any electrical wires or switchs that tend to periodicly shut down? Any help would be apprieciated,
Thanks Craig

Ranger Smith · 06-17-2015, 06:42 PM

I have the same issue with mine. I installed new compressor and dryer, evacuated, and properly charged system. It seems to me that the only thing I can think of is there are no electric fans on mine and when it gets too warm it shuts down. I have tested low and high pressure cutoff and both OK. I never figured it out yet.

Hikerdogs · 06-17-2015, 07:09 PM

There are several reasons the AC might shut down. In your case it sounds like there might not be enough Freon (R134A) in the system to maintain the minimum pressure required to keep the compressor running.

There's both a high and low pressure switch. That have to be satisfied to keep the compressor running. The pressure has to be above the minimum to allow current to flow through the low pressure switch to the clutch magnetic coil. The pressure also can't be too high or it'll open the high pressure switch and stop current to the clutch coil.

We had a situation with our 2001 Adventurer where there was enough pressure for the compressor to run, but the Freon pressure was low enough that in hot humid weather the evaporator coil would freeze over. With a coating of frost over the coils no air could pass through them so the air would slowly warm and eventually no air would come into the passengers compartment. The problem could be temporarily resolved by shutting off the system and letting the frost on the coils melt. Then it would be good for another hour or so before it froze over again.

If the pressure is low it's likely caused by a leak. It could be something as simple as a loose fitting or blown o ring. It could also be something like a cracked tube or stone thrown into the condenser in front of the radiator.

There are dozens of other reasons the air might get warm. It could be the compressor clutch burnt out, the blend doors bind, loss of vacuum to operate the blend doors, a bad water shut off valve, etc., etc.

In this case it's best to take it back to the shop. They can put the gauges on it to determine if there's sufficient Freon in the system, and check and/or bypass the switches and valves one at a time to determine the cause. Without the proper equipment to diagnose the problem you'll just be guessing. You might get lucky and find the problem with the first guess, or you might spend days and a boat load of money before getting it right.

hondo12 · 06-17-2015, 07:24 PM

thanks guys for your input, I put my head under the dash to see if I could see anything out of the ordinary, wow thats a cluster I wouldn't want to dig into!
I was able to hear a vacum air sound each time I turned the A/C max and A/C swith on and off .... does any know if there is a coach A/C wiring diagram on the forum?

Hikerdogs · 06-17-2015, 08:37 PM

Unfortunately there aren't any available through Winnebago. It's sort of a grey area in that Ford and Winnebago each supply some of the parts. Your best bet would be to get a Ford Truck service manual that covers the F550 and the F53 stripped chassis.
The best one to get is the original Ford manual on CD. Be sure to get one that covers all the trucks. They make several versions. Some only cover the F150 - F350. Others cover an individual model, and others cover the complete line of trucks from the Expedition to the F750 and F53 stripped chassis.

I see them all the time on eBay. The one that covers the complete line of trucks usually goes for around $50.00

hondo12 · 06-17-2015, 08:53 PM

Good idea, Thanks, mine is a workhorse chassi so I will check thier site..

Ranger Smith · 06-18-2015, 04:07 AM

Quote:

Originally Posted by hondo12

Good idea, Thanks, mine is a workhorse chassi so I will check thier site..

If you PM me I will send you a copy via PDF via your email. Everyone always seems to think that when you have an AC problem it is always "low on freon". All those signals for the AC go to the PCM and control it accordingly. There is some signal telling the AC to shut off. Haven't figured it out yet but I will. When mine kicks in the pressures are fine. Mine worked all the way from Florida to Mass with no issues. I still think there is a heat sensor somewhere telling it to shut off.

hondo12 · 06-18-2015, 12:12 PM

so as an update to my dash A/C dilemma, this morning I thought just for the heck of it I would start up the MH and turn on the A/C and it worked perfectly!! remember yesterday it didn't work at all the day before that it did and so on??? the only thing I did was fill the GM coolant reservoir under the hood ..... Crazy !!

wa8yxm · 06-18-2015, 12:48 PM

Why would the coach shut it down for safety of mechanical.. I can think of a very good reason but alas the folks who program the control computers have yet to figure it out.. So they do not do it.

(Under heavy engine load kill A/C to gain a couple HP).

But that said.. I can think of why it would shut it down for ELECTRICAL reasons.

I am fond of a saying: Many RVers have a few screws loose.. Does not (exactly) apply here (I will explain it) but I think you have one of two issues.
A loose connection (IF the blower continues to blow)

OR... a almost broken wire.

The screws loose: I had issues with the roof air not working till I got into the power distribution panel (Breaker box) and tightened the screws.. one took over 2 full turns BEFORE I FELT RESISTANCE and over another full turn to tighten. Several were loose including one on my INLET.

And one RVer all SIX of the screws inside his Marinco outlet.. You guessed it.. Outlet fell off in my hand when we went to check for voltage.

Hikerdogs · 06-18-2015, 02:49 PM

GM uses an orifice tube to change the high pressure liquid in the system to a low pressure gas just as it enters the evaporator core. The expanding low pressure Freon (R134A) is much cooler than the high pressure liquid. As the cool gas travels through the coils air is blown across them. The cooled air is then routed through the passenger compartment.

This orifice tube also has a fine screen type filter on the inlet side to prevent debris (dirt, o ring material, moisture, and other contaminants) from being circulated back to the compressor. If the system has ever been opened and not evacuated properly, dirt (dust) and moisture could be in the system.

If opened the system should be evacuated with a vacuum pump to 29" of mercury for a minimum of 30 minutes. This will allow any moisture to boil off and any contaminants to be sucked into the vacuum pump filter.

If there is moisture and contaminants in the system they will not pass through the filter on the orifice tube. If there's sufficient moisture it will eventually collect at the filter and block the flow of Freon. After the system sets idle for some time the pressures on both sides of the filter normalize. The moisture will go back into suspension and remain there until the system is restarted. Eventually enough will once again collect on the filter screen and block the flow of Freon through the orifice tube. When that happens you'll loose cooling.

There's no set time as to when sufficient moisture and dirt will cause the filter to clog. Any dirt collected will likely remain trapped in the filter while the moisture will go back into suspension. The harder the system has to work the quicker the filter will collect the moisture.

Keep in mind the compressor does not necessarily pump at the same rate of for the same amount of time each time you run the air conditioner. On some systems the pump runs continuously, but at very low pressures once the inside temperature demand is met. Other systems will cycle the compressor on and off depending on the demand temperature.

winnie32v · 06-23-2015, 07:53 PM

Great mystery...let us know where you end up.
Thanks

bruceisla · 06-23-2015, 08:08 PM

My intermittent dash A/C problem turned out to be a defective "cold control".
The contacts would open if I tapped on it. It is in series with the compressor run circuit. Mine is an Evans Temcon ... if you have one of these you can jumper around it to test.

hondo12 · 06-23-2015, 11:59 PM

Hello, I have gotten to the point that im out of idea's , what i know for sure that if the inside of the coach isn't real hot,like first thing in the morning the ac works great , air temp down to 42 degrees, but if in the afternoon with 70 to 80 inside temp the air never gets below 60. Im at the conclusion that the ac Recirculates the inside air and isnt strong enough to bring it to cold. I am anxious to try and locate that cold relay and go from there, thanks for all the input i really apprieciate it .... craig

bruceisla · 06-24-2015, 02:59 AM

Quote:

Originally Posted by hondo12

Hello, I have gotten to the point that im out of idea's , what i know for sure that if the inside of the coach isn't real hot,like first thing in the morning the ac works great , air temp down to 42 degrees, but if in the afternoon with 70 to 80 inside temp the air never gets below 60. Im at the conclusion that the ac Recirculates the inside air and isnt strong enough to bring it to cold. I am anxious to try and locate that cold relay and go from there, thanks for all the input i really apprieciate it .... craig

I'm not sure what yours looks like but mine is like this:
The "freeze sensor/thermostat" is also known as "cold control" ... it has a long tube that reaches inside the evaporator housing and detects a core freeze.

hondo12 · 06-24-2015, 06:16 PM

Thanks for that picture my control was in the same place yours is, I did jumper around it and it did blow 40 degree air! contiuosly, trying not to let my self get to excited just yet until I have the chance to try it when its very hot in the coach. So wondering how hard is this to change out? the cooper tubing is very tight in the heater box can you give me some pointers, Or what would happen if I left it jumpered for a while as I have a trip at the end of next week. Thanks again for all the info and pictures?

bruceisla · 06-25-2015, 04:01 AM

Quote:

Originally Posted by hondo12

Thanks for that picture my control was in the same place yours is, I did jumper around it and it did blow 40 degree air! contiuosly, trying not to let my self get to excited just yet until I have the chance to try it when its very hot in the coach. So wondering how hard is this to change out? the cooper tubing is very tight in the heater box can you give me some pointers, Or what would happen if I left it jumpered for a while as I have a trip at the end of next week. Thanks again for all the info and pictures?

The tubing is rather stiff. Once you remove the screws holding the switch body, it should pull out. The tubing may have caulk/putty where it enters the core. Shape the new tubing like the old one before you insert it.

The primary purpose of this device is to detect a "too cold" condition ... or an evaporator freeze. In the event of a freeze,it shuts down the compressor until the freeze is gone (the freon is once again a liquid). It's unusual for a freeze to occur in a dash A/C. While I was waiting for my new part, I jumpered mine ... but I did replace it as soon as the part arrived (5 days).

If you take it apart, it looks like typical wound bimetal spring thermostat ... mine had badly burned contacts and was not repairable.

hondo12 · 07-05-2015, 03:38 PM

Thanks ! installed new cold tstat and it a/c working alot better now...