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Old 08-04-2014, 11:51 AM   #1
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Hot Air Through Dashboard Vent

Hi everyone. I have a Jayco Greyhawk with a Ford E-450 engine. I am getting very warm to hot air through the dashboard vent when towing a vehicle and using the "tow-haul" setting. The engine appropriately revs higher and thus is a bit hotter but in the normal operating range. I took it to the Ford dealership and was told everything is working normally and that about 80% of the vent air actually comes through the front grill and flows over the engine, which is why it is hot. They recommended I use the A/C setting, or the Floor/Vent Mixture setting as both engage the air-conditioner compressor motor and thus cool the air. However, if I'm going up a steep hill and/or traveling in very hot conditions it doesn't make sense to me to put more strain on the engine by using the air conditioning compressor. If any of you have encountered this issue and found a solution I'd appreciate any insight you can provide. I also get some excessive heat leaking through the dog house and appreciate the great suggestions I read on this site to address that issue. Thanks!

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Old 08-04-2014, 12:37 PM   #2
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Can you just shut the vents?

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Old 08-04-2014, 01:32 PM   #3
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I can turn the dashboard selection setting to "off", in which case no air comes through the vent, which also gets a bit stifling given the hot air leaking around the dog house. I'm addressing the dog house issue separately and I'm hoping to find a way to vent a greater percent of the outside air through the dashboard and less (or no) of the hot air flowing over the engine. Thanks for reading and responding to my post.
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Old 08-04-2014, 02:32 PM   #4
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The Stealership lied to you. It's both illegal and stupid to have the air from the engine bay introduced into the vents. What would happen if you had an exhaust leak? Or even just a rad hose burst? You want a cabin full of boiling hot antifreeze mist?

The air intake for the HVAC system (except recirculate obviously) comes from the cowl, the area between the hood and the windshield. It does not matter what position the selector is in, if it's getting outside air, it's coming from the cowl there is NOT two sources of air. Further, the A/C cycles when the defroster is on, not the floor setting. Find a new dealer.

More than likely the valve that determines how much water gets to the heater core failed or the mechanism that adjusts it. As a simple test you can take long nose locking pliers (Vice-grips) and just barely pinch one heater hose closed then go for a drive.

I'll bet the problem is gone.
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Old 08-04-2014, 06:42 PM   #5
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The heater core indeed makes a lot of sense based on my past experiences with rigs that didn't have A/C and thus the problem was masked.

If the comment was that it was hotter while under load, an air leak in the firewall or the doghouse would be the next thought, but that wouldn't be felt through the vents in the dash.
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Old 08-05-2014, 02:59 PM   #6
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Thanks Murf2U and wanderso. When I went to the Ford dealer I questioned what the service technician was telling me as it didn't make sense to me that hot air would come through the engine compartment into the vent system. I also asked about the "radiator core" since I couldn't find it under the dash (I repair I made decades ago on my first car). He insisted they don't use a heater core in the dash any more and haven't done so for several years, which explains why I couldn't fine the hoses. He stated that the vent setting is an electronic switch that opens and closes a "dormer" (I believe that was the term he used) that determines how much of the vent air comes through the engine compartment vs through the vent opening at the base of the windshield. Seems very odd (and potentially dangerous as you suggested) for engine compartment air to be vented through the passenger compartment. Most notably if there was an exhaust leak the passengers could get carbon monoxide poisoning, so it would be foolish to vent engine compartment air through the vent system. You've given me the motivation to take another look at the system and see if I can figure out where the vent air is coming from. Thank you for your responses.
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Old 08-05-2014, 06:32 PM   #7
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There's a bit of confusion here and I don't think your dealership explained it to you the right way. Heater core is still there just like it was in the 90's. Only three common ways to heat an auto. Heater core (hot water from engine block), heat exchangers (heat from exhaust - mostly used on air cooled engines), and heat pump (from running ac compressor backwards - seeing more use age on electric and Hybrid autos).

With that said, auto makers don't use vales to limit or stop the flow of hot water to the heater core anymore. They found it causes air bubbles and early heater core failures as 8 mounts of the year water stays in the heater core without circulation of anti-corrosion inhibitors.

Heater cores now use a blender door to divert the air flow through the heater core (heat mode) or around it (ac mode). These blender doors are known to stick. So, it's possible your blender door is stuck diverting air through the heater core... Ie hot air coming out your vents as though you have selected HOT.
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Old 08-06-2014, 08:47 AM   #8
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Thanks sca. Your insight is very helpful and makes a lot of sense. The dealer did mention they checked the door you referred to and it was working normally. I presume that door supposed to be closed when the vent setting is selected and the temperature selector is set to cold, but I do get hot air out of the vent as if I had turned the temperature selector to hot (i.e. the extreme end of the red zone on the dial). I looked under the hood and noted that the air intake for the vent system sits directly above the radiator (and actually points "down" so hot air from the radiator theoretically can get sucked into the vent intake). Do you think it would make a difference if I simply re-position the air intake so that it is getting "fresh" air from the front of the vehicle? That's what I'm going to try next. I'm also contemplating disassembling the plastic tubing that appears to connect the vent intake to the engine compartment side of the dashboard to evaluate the operation of the door you mentioned. I truly appreciate your insight and response.

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