Heat/Defrost control

NANLAR · 11-29-2021, 06:23 PM

I have a 2018 Jayco Precept, 31UL. The heat/defrost contorl is not working. When the engine is running, I get heat out the vents, but if I move the switch to floor or defrost the air flow does not change. It still comes out the dash vents. Interesting thing is that if I set the switch to floor, turn the engine off for 5 to 10 minuets, start it back up, the air will be all on the floor and not the dash vents. Move the switch back to the dash vents and nothing happens. Can't go to defrost either. Any ideas where to start looking?

RogerR · 11-29-2021, 07:23 PM

In the past vent controls worked on vacuum. There was a little rubber hose that run from somewhere in the motor air intake system to the dashboard. The control knob was a multi-position knob that would direct this vacuum into different positions to open or shut a little door that directed the hot air into various channels.

First thing you can do is listen under the hood for a hissing sound. If you can track it to a piece of tubing then inspect it and try to find the leak. A temporary tape patch may make a fix until you can replace it. Or someone may have pulled one end almost off the port and you need to push it back in. There are other solutions and problems like a bad door. Or yours might run on 12 volts and you have a bad switch or gremlins and the chassis dealer can find in a $150 heartbeat. And maybe fix it for less than the MSRP of a new rig.

RPR · 11-29-2021, 08:20 PM

On many systems if there is no vacuum or low vacuum the vent control will default to the defrost vent setting. Safety measure so you can see out. With what you described I would lean toward the device that switches vent settings.

Parrott · 11-30-2021, 07:04 AM

I had an issue with my Precept. When putting the control to vent I was getting a clicking noise. Mine would only blow defrost. It ended up being a smart control module. There are 2 of them. One being fairly easy to get to and one not so easy. Turned out mine was the not so easy one way up in the dash. Replaced and fixed mine. They are electric. They control the air flow doors to direct the air flow.

Parrott · 11-30-2021, 08:04 AM

Here is a link to some good info.
Electric actuators.

https://www.proairllc.com/pub/media/...Assemblies.pdf

Parrott · 11-30-2021, 08:35 AM

Here is a picture of mine on the passenger side from the floor. It’s the easy one. You can put your hand on it and turn your selector knob and feel if it’s operating. You can actually see the piece I circled in yellow turn if it’s working. Hope it’s this one for you. The other one is located further back in the dash and you have to remove the black plastic trim piece which is a pain. It is kind of hard to see even with the black plastic removed.

NANLAR · 11-30-2021, 08:59 AM

Thanks for the info. Is the only way to test the is by feeling it turn? How did you determine whitch switch it was?

Parrott · 11-30-2021, 09:08 AM

Quote:

Originally Posted by NANLAR

Thanks for the info. Is the only way to test the is by feeling it turn? How did you determine whitch switch it was?

You can actually see the part I circled in yellow turn if it’s working. Mine was making a clicking noise like nylon gears were stripping. It was the one up under the dash you can’t get to without removing the black plastic trim piece. You can lay on the floor and turn the selector knob with your left hand to see if the one in the picture works.

NANLAR · 11-30-2021, 06:26 PM

Are both the smart control modules on the passanger side?

Parrott · 11-30-2021, 06:40 PM

Quote:

Originally Posted by NANLAR

Are both the smart control modules on the passanger side?

Yes but the hard one to get to is up inside the dash. You can’t see it without removing the black plastic cover piece. If you could see through the black plastic, it would be inside below the left dash vent.

NANLAR · 11-30-2021, 06:42 PM

Thanks! I willcheck it out next week. Thanks for your input. It really helps!

Parrott · 11-30-2021, 06:47 PM

The one in the picture follow the red line up under the dash. Hopefully that’s the one that is bad and you will not have to take the black plastic piece out as it’s a pain.

NANLAR · 11-30-2021, 06:58 PM

I know getting that black piece off is a pain. I had to take that off to get the "dog house" off last year! Hope i don't have to do that again! Thanks again!

Parrott · 11-30-2021, 08:09 PM

Quote:

Originally Posted by NANLAR

I know getting that black piece off is a pain. I had to take that off to get the "dog house" off last year! Hope i don't have to do that again! Thanks again!

I took my doghouse off through the center console. Finding the 2 screws inside through the carpet was tough. I removed the carpet and painted mine with epoxy with a little texture in it. The hard part putting it back in was all the wires hanging down. I cut a piece of 1/4” plywood and put it across the bottom of the console hanging on the plastic lips making it easy to take out and install. I didn’t put screws back inside the console. I put 2 layers of Kilmat inside while it was out.

MJD · 12-26-2021, 01:26 PM

I was just going to post about a similar problem I am having . (2018 Alante 31R). I can get air coming out the windshield vents and the floor vents, but nothing out of the main vents. I can switch from defrost to floor, but nothing out of the A/C. Vent.

Any suggestions?

RogerR · 12-26-2021, 01:39 PM

Most older vehicles used vacuum produced by the running engine to change the way the air flow vents via a control knob. Some newer vehicles use an electric vent control. Others use an electric motor.

If yours is a vacuum type look for a tiny leak in a vacuum line. Alternatively but less likely there could be a bad control knob/valve.

If it is electric check for a bad fuse. If all good could be a bad control switch.

After that you may need the chassis brand dealer or a good mechanic to diagnose and repair.

MJD · 12-26-2021, 02:33 PM

Thanks, for the information.

Parrott · 12-26-2021, 08:18 PM

Quote:

Originally Posted by MJD

I was just going to post about a similar problem I am having . (2018 Alante 31R). I can get air coming out the windshield vents and the floor vents, but nothing out of the main vents. I can switch from defrost to floor, but nothing out of the A/C. Vent.

Any suggestions?

You most likely have the same actuators. They control the doors redirecting the air flow.

MJD · 12-27-2021, 08:33 AM

Thanks Parrott.

MJD · 03-02-2022, 12:52 PM

It’s been a while on this , but just getting the MH serviced ready for the season. Had the shop check my switch problem and it is exactly as Parrott described. Repair is on its way should be good to go soon enough. Just wanted to give a shout and thanks for all the responses.

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