Dash Air Only "Hot" After Startup

[toneyamurphy]

I have a '13 HR Ambassador with a dash air discharge problem.

When I first start the engine and with the a/c control's set on cool I get very cold air out of the a/c dash vents. However, as the coach engine warms up the a/c air begins to warm up also until all I have is hot air coming out of the dash vents.

I cannot find any fuse or circuit breaker blown or tripped. The controls on the a/c control panel are in the proper position for cool air.

The air compressor hoses under the front generator area are cold and cool.

The heater hoses coming from the electric hot water valve is "hot" supplying the heater coils and cooler returning.

I have replaced this electric hot water valve thinking that may be the problem.The new valve did not resolve the situation.

This all started during a return trip of camping.

Any help is appreciated.

Toney, F409212

[dave111451]

Almost has to be one of two things.Either hot water valve not shutting off water or blend door not shutting off hot air.I would lean towards blend door problem.Either something stuck in door or actuator bad or out of adjustment.

dave

[dickandlois]

Toney,

From your description, it sounds like one of the baffle doors is stuck. These doors open and close as needed to mix the AC(Cold air) and the hot air supplied from the different sections of the mixer box.

The most common problem is the seals get sticky and hold the doors closed so you can not get the proper air temperatures blowing out different vents.

The other possibility is one of the vacuum actuators is defective or broken.

Thing is you have a 2013 model year, if I'm reading your post correctly and in that case the mixing box assembly should not be the issue, But stranger things have happened.

So the only item that would make sense to me would be a vacuum control problem or a vacuum pump issue. The fact that you can select where the air is directed, Windshield defroster, dash vents and floor kind of muddies those thoughts also.

The problem should be in the mixing box, as long as you have cold AC lines and hot lines on both the input and output of the box.

Rich.

[toneyamurphy]

Almost has to be one of two things.Either hot water valve not shutting off water or blend door not shutting off hot air.I would lean towards blend door problem.Either something stuck in door or actuator bad or out of adjustment.

dave

I have to think both responses are correct. I'll contact the factory tomorrow and ask for a diagram of the air flow. thanks for responding.

[toneyamurphy]

Toney,

From your description, it sounds like one of the baffle doors is stuck. These doors open and close as needed to mix the AC(Cold air) and the hot air supplied from the different sections of the mixer box.

The most common problem is the seals get sticky and hold the doors closed so you can not get the proper air temperatures blowing out different vents.

The other possibility is one of the vacuum actuators is defective or broken.

Thing is you have a 2013 model year, if I'm reading your post correctly and in that case the mixing box assembly should not be the issue, But stranger things have happened.

So the only item that would make sense to me would be a vacuum control problem or a vacuum pump issue. The fact that you can select where the air is directed, Windshield defroster, dash vents and floor kind of muddies those thoughts also.

The problem should be in the mixing box, as long as you have cold AC lines and hot lines on both the input and output of the box.

Rich.

Rich and Dave, When we bought the coach I could only get hot air. The seller/dealer had his mechanic to go into the nose area and fixed the problem. We had good cold air after that and was able to go to hot and back to cool with no problem. Now after two+ years it has raised it's ugly head again and I'm stuck on hot. After I talk to the factory rep tomorrow (asking for diagram) I'll crawl through the nose area to see if I missed anything. I'll be looking for loose or corroded wires and anything else that may be causing the problem. I don't know how to get to the mixing box or the actuators unless I have to take the dash out. That is way above my head.

You all have sent me on the right direction and I appreciate that. Thank you both, Toney

[manholt]

Can you talk to the mechanic who fixed it 2 years ago? Or the dealer?

[toneyamurphy]

Can you talk to the mechanic who fixed it 2 years ago? Or the dealer?

I have his number in my service file and will try to reach him Monday. Thanks for responding. Toney

[DBianchini]

My 97' HR has had a similar problem, for me it was vacuum hose leaking, not pulling one of the mixing box doors closed. Finding the leaking part was hard. Diagnosing the problem was caught by switching the dash controller from cool to hot, dash air to floor air etc. The vacuum pump ran longer ( continually) when it tried to move the mixing door. Most of my hoses were up behind my dash.

Good luck.

[wayne77590]

I have had all the above checked as my dash AC would start out cold and rapidly increase to warm. Had it checked at Freightliner this past Summer and they found two service valves leaking and a condenser valve leaking. I did not have time for them to repair it right then as they had to order parts. Recently (like last week) it went to an automotive repair facility that also works on RV engines (Taylor Automotive, Dickinson, TX) and they not only found the valves leaking but there was something else wrong. I have not had the full report back yet. We lived with the problem for a few years and just ran the house AC while going down the road.

I'm mentioning all this to indicate that a full service center should do a leak test to preclude that problem, after all else is checked.

[toneyamurphy]

My 97' HR has had a similar problem, for me it was vacuum hose leaking, not pulling one of the mixing box doors closed. Finding the leaking part was hard. Diagnosing the problem was caught by switching the dash controller from cool to hot, dash air to floor air etc. The vacuum pump ran longer ( continually) when it tried to move the mixing door. Most of my hoses were up behind my dash.

Good luck.

Thanks for responding. Just one question. Did you have to pull the dash panels to get to the leaking hose? On the '13 I don't know where or how to start pulling. I do get good hot air from the floor, dash and windshield defogging vents. Just no cool air when selected. It is leading me toward a loose or disconnected vacuum hose under the dash, I'm going to talk to the factory rep. tomorrow a.m. asking for a schematic and any input they may have. Your response is inline with the others i'v received and I think all are correct. , Toney F409212

[DBianchini]

Toney,

My RV is much older (97') I had a large in dash (30lbs) tv. I removed it and could see most of what I needed. It was still a spaghetti mess. Heat was my enemy and caused the 1/4" od rubber tubing to become brittle. Earlier, more leaks were found behind what would be my front grill in the generator area. Many days traveling in dry hot temputures ruined most of those tubes 7 + years ago and were replaced by me. They dont make it easy to work on.

[toneyamurphy]

I have had all the above checked as my dash AC would start out cold and rapidly increase to warm. Had it checked at Freightliner this past Summer and they found two service valves leaking and a condenser valve leaking. I did not have time for them to repair it right then as they had to order parts. Recently (like last week) it went to an automotive repair facility that also works on RV engines (Taylor Automotive, Dickinson, TX) and they not only found the valves leaking but there was something else wrong. I have not had the full report back yet. We lived with the problem for a few years and just ran the house AC while going down the road.

I'm mentioning all this to indicate that a full service center should do a leak test to preclude that problem, after all else is checked.

First of all "Thank you for your service to this country of ours". I too am retired Air Force with 38 years service mostly as a Flight Engineer on the C-130 bird. You would think I could just jump into the middle of this and trouble shoot, find the problem fix it and be done with it. But getting under that dash has me baffled. No pun intended. It turned bitter cold last night so I'm stuck to researching right now. This thing is more complicated than my C-130 , at times. Thanks Again, Toney 409212

[wildebill308]

Rich and Dave, When we bought the coach I could only get hot air. The seller/dealer had his mechanic to go into the nose area and fixed the problem. We had good cold air after that and was able to go to hot and back to cool with no problem. Now after two+ years it has raised it's ugly head again and I'm stuck on hot. After I talk to the factory rep tomorrow (asking for diagram) I'll crawl through the nose area to see if I missed anything. I'll be looking for loose or corroded wires and anything else that may be causing the problem. I don't know how to get to the mixing box or the actuators unless I have to take the dash out. That is way above my head.

You all have sent me on the right direction and I appreciate that. Thank you both, Toney

I would start in the nose area not under the dash if that was where the problem was before. Use a piece of hose to listen for air leaks.

Bill

[wayne77590]

Toney,

Under the front hood is a device that controls the damper door via vacuum. The ends tend to crack and leak, dry out, slip off and who knows what else. It will keep the damper door from switching over to hot/cold etc. It looks like a little silver ball but can be of any shape. there will be one line going to it. That line is controlled from inside when you turn the control knob from blue (cold) to red (hot), it provides the vacuum to open and close the damper door. The line COULD leak or have a problem behind the control knob. Give it a check.

Thank you for your service also.

Hey, you were trained on the C-130, but did you get training on the MH.

[toneyamurphy]

Toney,

Under the front hood is a device that controls the damper door via vacuum. The ends tend to crack and leak, dry out, slip off and who knows what else. It will keep the damper door from switching over to hot/cold etc. It looks like a little silver ball but can be of any shape. there will be one line going to it. That line is controlled from inside when you turn the control knob from blue (cold) to red (hot), it provides the vacuum to open and close the damper door. The line COULD leak or have a problem behind the control knob. Give it a check.

Thank you for your service also.

Hey, you were trained on the C-130, but did you get training on the MH.

No, it was give me your money here are the keys now get lost, kid. LOL. In reality we spent the better part of three days going in/under/over/around the MH. A few minor problems were addressed and all questions were answered. This problem came up and was fixed with the mechanic going under the hood and all was well for about 2 years. As soon as I'm able I am going under the nose area again following your suggestion as written above.

I just hope my problem has a simple solution and I'm not making a mountain out of a ant hill.

Later, Toney

[toneyamurphy]

Toney,

My RV is much older (97') I had a large in dash (30lbs) tv. I removed it and could see most of what I needed. It was still a spaghetti mess. Heat was my enemy and caused the 1/4" od rubber tubing to become brittle. Earlier, more leaks were found behind what would be my front grill in the generator area. Many days traveling in dry hot temputures ruined most of those tubes 7 + years ago and were replaced by me. They don't make it easy to work on.

I agree with you (they don't make it easy ). Thanks for responding.

[toneyamurphy]

I have his number in my service file and will try to reach him Monday. Thanks for responding. Toney

Could not find his number today, Monday, but will be working on it Tuesday. Thanks, Toney

[greenbarn1]

Had same problem. Actuator valve in front of coach. Access by pulling front nose out. I put a 5/8 quarter turn made to handle high temperatures. So when weather is hot I shut valve stopping hot water mixing with cold air.. Works perfect.

[toneyamurphy]

Had same problem. Actuator valve in front of coach. Access by pulling front nose out. I put a 5/8 quarter turn made to handle high temperatures. So when weather is hot I shut valve stopping hot water mixing with cold air.. Works perfect.

I may have to do the same but am wondering about defrosting when I need it. Did you mean a 5/8inch shut off valve in line on the hot water line between the heater coil and the electrical shut off valve?

That sound like a good idea but I have already checked with Lowes and they do not carry these.

Thank you very much for responding.

Toney,

[greenbarn1]

Yes, I used a quarter turn used on hot tubs. Worked perfectly. Actuator was not closing so as coach warmed up I lost a/c. I never have needed a defroster in a class a motorhome. If in cold weather I turned valve open.

[toneyamurphy]

Yes, I used a quarter turn used on hot tubs. Worked perfectly. Actuator was not closing so as coach warmed up I lost a/c. I never have needed a defroster in a class a motorhome. If in cold weather I turned valve open.

This may be my best solution for the short run. Thank's greenbarn1 for your response.

Could you tell me the Model of coach you used this solution on?

[toneyamurphy]

I talked to the factory rep. yesterday and he said yes indeed they were having problems such as this and found the fan box or

plenum box was not sealing properly. Their solution was to run duct tape around edges of this housing box. I don't know if this

will work or not but it is worth a try. It sounds like a fast solution to a problem that if this is the cause will raise it ugly head when the tape starts peeling. It's 17 degrees out so will have to wait a day or two for warmer weather.

I did find out all or most all the mechanical portion is "ender the hood" but it is hard to get to due to the massive amount

of wires, tubes, hyd lines, etc.

[toneyamurphy]

Well, as it warmed up I went back "under the hood" again and it appears the fan/baffle box can be assessed from there. I found no way to cut the hot water, radiator mixture, from under there. I did check the only fuse powering the fresh air/heater system and I got continuity through all three fuses that were on the same "block". So no fuses were blowned. By this time the cold was getting too much for me so I quit and went to Loews for supplies. It is suppose to warm up to 55 in next couple of days then back down to single digits for three days. Thanks All for your help and input, Toney, 409212

[greenbarn1]

2001 Newmar Dutchstar.

[wayne77590]

 

I talked to the factory rep. yesterday and he said yes indeed they were having problems such as this and found the fan box or

plenum box was not sealing properly. Their solution was to run duct tape around edges of this housing box. I don't know if this

will work or not but it is worth a try. It sounds like a fast solution to a problem that if this is the cause will raise it ugly head when the tape starts peeling. It's 17 degrees out so will have to wait a day or two for warmer weather.

I did find out all or most all the mechanical portion is "ender the hood" but it is hard to get to due to the massive amount

of wires, tubes, hyd lines, etc.

Toney,

Don't use duct tape, get some AC tape. It's the silver stuff that is use in all AC work around plenums. It lasts years before peeling, if ever.