Hot air from vents when slowing down

[INSPECTORBOB]

This past week-end was our first real trip in our 2000 Itasca Suncruiser. While setting the dash control function to the "vent" or "heater" (no a/c) position and the temperature turned all the way to cool, the air coming out of the vents or heater was fine--about the same as the outside temp, as long as we were moving at a pretty good clip. However, as soon as we slowed to 20 to 30 mph, the temperature of the air coming out of the vents got really hot. Not just warm, but about as hot as you would expect it to get if the heater was turned all the way up.

Any ideas?

Thanks,

Bob

[John Mo]

I think this is just the nature of the beast. My '08 chassis F53 has done this since new. I don't think there's a problem with a valve failing anywhere or a vacuum failure (though vacuum problems are common in Ford HVAC switching). I think when you slow down or stop that the heat just can't dissipate adequately from the engine compartment and it soaks the HVAC ducts to the dash.

[wa8yxm]

Has to do with were the fresh-air intake is.. When you are moving SLOWLY heat rises from the engine to the place where they suck in the air, and thus you feel the heat

Hammer down and the heat from the engine is blown back, and down, and out, before it can rise to the air intake.

This is normal.

PAGE 2:

When you run air conditioning.. You may find the same thing.. TWO reasons for that, possibly 3

1: As above
2: The compressor is not cranking fast enough to do the job at low speeds and
3: (Actually kind of rare) Needs service.

[INSPECTORBOB]

Thanks for the replys, folks.
I don't think I have a mechanical problem either, because while underway, I can use the temp knob to adjust from cold to warm, and it works just fine, so I think that eliminates the possibility of a blend door issue.

But, when going slow, it is extremely hot. To the point that I either have to turn on the a/c to MAX, or just shut it off. I wonder if there is a way to reroute the air intake to get away from some of the heat in the engine compartment.

Bob

[Hikerdogs]

Actually I believe you do have a "mechanical problem" We have over 85,000 on a 2001 Winnebago Adventurer on the same chassis. In all those miles we've never experienced HOT air comming through the vents at low speeds. The air may warm a few degrees as it flows through the engine compartment, but it never gets hot.

I suspect you have a leaking heater control valve. Either there's a vacuum leak not allowing the valve to fully close or the valve itself is letting a small amount of hot water to flow through the heater core. At higher speeds there is sufficient cool air passing over the heater core to absorbe the small amount of heat comming from the coolant. As your speed decreases the outside air flow lessens and the heat is more noticable.

An easy way to check is feel the heater hose on both sides of the valve. When the temp control dial is set to the low position it should be warm on one side and almost ambient temp on the other side. If both sides are hot water is flowing through the valve.

[INSPECTORBOB]

Hikerdogs, this makes alot of sense. Thanks. Where do I find this valve?

Bob

[Hikerdogs]

The valve in our coach is under the hood on the passengers side in front of and above the heater. It's silver with a domed top. The vacuum hose attaches to a small tube on the top and the heater hoses attach to the lower section with one comming in from the right and the other from the left. Your valve may have a slightly different configuration but all heater valves used by Ford look basically the same.

This valve only controls the heat comming out of the dash vents. There is no temperature control for the floor register just behind the engine cover. This register is part of the Motoraid system. The motoraid system uses a heater core similar to the one in the dash. It keeps the water in the water heater hot when driving and supplies hot air to the passengers compartment through the single floor register. There is a 3 position fan switch that controls the blower for this unit on the lower section of the dash. When the top of the switch is depressed toward the dash the fan should be on high speed. When it's parallel to the dash the fan should be off. When the bottom of the switch is depressed toward the dash the fan should be on low speed.

[INSPECTORBOB]

I will look for the valve when I bring it out of storage this week-end. Thank you!

Bob

[rini2]

We have a 02 Suncruiser 32V, Ford Cassis, new to us last summer, with the same issue. In all but "max/AC" the air from the AC vents is hot. The air somewhat cooled in normal AC setting, but not what you would expect. My assumption is that in normal AC mode outside air is still being drawn into the coach and the AC core is having to overcome the heater core heat along with the outside air. I was thinking that either the air damper wasn't closing properly isolating the heater core from the air stream or the heater control valve was not fully closing. The hot air coming from the vents did not cool even at highway speeds with the outside temps being the 55-60° range. Thus even at those temperatures we found it necessary to travel in the max/ac setting. Reading the other posts, I will investigate further in the spring once I take our motorhome out of hibernation.
Jeff

[KC1BUD]

GM and Ford use a vacuum operated valve and they often stick partly in both positions.