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Topic: Dash air conditioner blows warm only. (Read 401 times) previous topic - next topic
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Dash air conditioner blows warm only.
Hi Group,
This is for my 2005 26' mid bath.
I was really hoping to get through this 2 month trip unscathed, but just 2 days before getting home, the dash (cab) air conditioner just started blowing warm air only. I pulled into a gas station and discovered the gas cap very loose. Thinking the extra stress on the engine going over a mountain pass might have caused a lack of vacuum making the AC shut dow I tightened it and resumed driving. Back on the road, the AC was cooling again until we reached the RV Park just 10 miles down the road. Lucky guess, problem solved? Naw.

Jump to this morning, on the road for about 20 minutes, the nice cool air from AC started going warm and stayed that way. After pulling in this afternoon, I tried it again and it seemed to be cooling, but again warmed up quickly. I'm sure this is going to take a trip to my mechanic, but any suggestions about what the causes could be? No changes noted on the instrument panel.

Thanks,
David G
2005 MB
Re: Dash air conditioner blows warm only.
Reply #2 –
Quote from: rich  - 
This could be another case of the common issue many of us have had.  There is a vacuum leak and you can bypass the leak and restore regular function.
Rich

Thanks for this Rich. Reading those posts, mine issue seems a bit different though. I still have air blowing, it just looses the coldness and becomes warm. I switched to vent to compare and the only difference seemed to be the fan switched off. The air temp coming out of the vents was about the same.

David G
2005 MB
Re: Dash air conditioner blows warm only.
Reply #3 –
Vacuum leaks and failed check valves can cause A/C issues. We just had a thread going on this topic a couple of weeka ago. 
Leaks can cause the HVAC ducting to act up and not provide the available cold air, instead letting in heated or outside air
Are you sure the A/C system is producing cold and has not lost its refrigerant due to a leak?

Larry
Larry
2003 23.5' Front Lounge, since new.  Previously 1983 22' Front Lounge.
Tow vehicles  2020 Jeep Wrangler Rubicon, 2001 Jeep Cherokee
Photo Collection: Lazy Daze
Re: Dash air conditioner blows warm only.
Reply #4 –
Quote from: Larry W  - 
Are you sure the A/C system is producing cold and has not lost its refrigerant due to a leak?

Larry

No not sure of that at all. It just started yesterday, so it could well be a leak. I don't know if there is a way to check for this until I'm home.

David
2005 MB
Re: Dash air conditioner blows warm only.
Reply #5 –
Hi David;  With air blowing out of vents, engine running but A/C off; you should be able to have air blowing out of the dash vents. Shifting to defrost, air should come out next to the front window at the base. Shifting to floor, the air should blow at you feet.  This checks to see if the vacuum is working, and that the various actuators can move flaps to steer air in the directions they should go.  If not, you don't have enough vacuum at the right places.
    The blend door control from 'cold to hot' knob on the dash, adds warm air to cold air from outside. Proper operation should change air coming out of the vent, lets say the upper dash vent, outside air, cool to hot.
     Usually critters chewing on hoses can cause sudden malfunctions. Pretty common, most of the hoses are not well protected (or at all).
     At idle turn on the air conditioning with air out of the dash about medium.  You should hear the compressor clutch 'kick in'. Don't have it set for maximum, it may not cycle off. At medium, you should hear it cycle on and off every few minutes.  The extra load caused by the Freon compressor, causes the engine control computer to increase the RPM just a little, and when the clutch turns off, the engine will slow down a little. You should have cold air coming out.
    If you have vacuum issues, leaks or disconnected hoses (really big leaks), The engine might run rougher.  When the engine is under heavy load, going up a hill, worse at high altitude, there may not be adequate vacuum to keep all of the actuated flaps in the A/C system where they belong. So the cold air might come out of the wrong places. Usually default as a safety feature, is defrost to allow you to see out clearly. (required by NHSTA)  The blend door might move around and let hot air dilute the cold air, so it might seem that the cold air went away, when really it is being over-powered by hot air.
    If it is a problem of low Freon, at idle the air might be cold, the compressor will only turn off for short periods of time, or not at all. At speed and hot temperatures outside, there isn't enough Freon to stay cold.  Small rocks can impact the A/C evaporator outside in front of the engine water radiator, and cause the Freon to leak out. You probably wouldn't hear anything, unless it was a really big rock. Thankfully the A/C radiator will protect your engine radiator! The oil cooler is more protected and smaller, the power steering cooler is also higher up and smaller.
    You can still run your generator and roof air while driving home.    RonB
RonB (Bostick) living in San Diego
Original owner of "Bluebelle" a '99 TKB
Re: Dash air conditioner blows warm only.
Reply #6 –
David, sounds to me like you are low on refrigerant. At idle the compressor would  kick in and maybe run for 30 seconds and kick out. As your engine revs this cycle would be faster yet. It would be cold for a while then warm up as you described. If you have a refrigeration buddy, your in luck. If not a shop might gouge the heck out of you so use caution. If you are mechanical you could probably add some refrigerant yourself. Just adding the gas gets you by, you have a leak and it must be repaired. Usual tell tail signs is an oily spot around joints and fittings. The big one is the compressor seal, these things don't get run alot and shaft seals will dry out. The other thing is a bad compressor clutch which could cause intermittent operation. Anything compressor wise though, you are going to need help.

Jon
1994 MB
Re: Dash air conditioner blows warm only.
Reply #7 –
Quote from: JonS  - 
David, sounds to me like you are low on refrigerant.

Jon


Thanks Jon and RonB. This seems to be what is happening. I do still have air coming out of each vent and described by Ron. On the way home, I got cold air initially, but it went warm about 20 minutes later, then occasionally it would cool down for a short while, then warm again. Seems like low on refrigerant and maybe a leak. I'll report back when I get it resolved.

David
2005 MB
 
Re: Dash air conditioner blows warm only.
Reply #8 –
If the A/C is actually blowing cold, refrigerated air, even for a short period shows the A/C system has refrigérant; it would not get cold without it. It may need additional refrigerant, but it has some in it.

My guess is it's a vacuum leak, as discussed earlier.
Several years ago, our LD's A/C stopped working or stopped blowing cold air. I replaced the tubing and vacuum storage cylinder undern the dash, along with a check valve. This mostly fixed the problem except when climbing on long upgrades where the engine's vacuum drops to near zero where the A'/C would drop out.
I used a smoke machine to fill the HVAC system and found the new Dorman replacement vacuum cylinder had a pinhole leak. It's frustrating how so many replacement parts are a junk.

Last summer, it started doing the same thing again, the A/C appearing to drop off when going uphill.  It was a loss of vacuum that caused one of the flaps under the dash to cut the air flow from the dash vents. The cause was a bad check valve. I carry a spare now.

Larry
Larry
2003 23.5' Front Lounge, since new.  Previously 1983 22' Front Lounge.
Tow vehicles  2020 Jeep Wrangler Rubicon, 2001 Jeep Cherokee
Photo Collection: Lazy Daze