How Dash Air Works - U320

Topic: How Dash Air Works - U320 (Read 2315 times) previous topic - next topic

Re: How Dash Air Works - U320

Reply #25 – June 29, 2021, 04:00:58 pm

Thanks TGordon. My blower location isn't readily apparent just by pulling the dash cover off. Any pics of the location?

I also read in another thread about a "bridge rectifier" that could also cause the fan not to run. Does anyone have a picture that shows the location? Any idea how to test or where to buy a replacement?

Re: How Dash Air Works - U320

Reply #26 – June 29, 2021, 05:37:36 pm

I have had a blower motor not working and it turned out to be a ground that was
riveted to the housing was loose. Hammered it tight and got it working.

Re: How Dash Air Works - U320

Reply #27 – June 29, 2021, 10:53:30 pm

I had to move the coach around today and paid specific attention to the AC. I turned it on and it seems that the blower is working, but only on low speed. It's very slow/low, but cold air is coming out. So it seems the blower is working, but not responding to the fan speed switch. The switch is new as of a month ago. What else should I be checking next?

Re: How Dash Air Works - U320

Reply #28 – June 29, 2021, 11:26:43 pm

In your wiring diagram I'm pretty sure you will see between the switch and the motor a resistance block for your lower speeds. And straight thru for hi speed. Real prone for corrosion issues. May be able to clean up or replace if damaged beyond repair.
Scott

Re: How Dash Air Works - U320

Reply #29 – June 30, 2021, 11:18:50 pm

I found the 4 wires coming from the switch and followed them down to a large cluster of wires at the center of the dash next to the metal box with the SGM sticker. From there, I can't see where they go without cutting zip ties and such. I also don't see an obvious blower fan location. Here are pics of the inside of the dash...where the heck is this thing? It sounds like it's under the center of the dash. I don't see how that comes off. Any hints?

Re: How Dash Air Works - U320

Reply #30 – June 30, 2021, 11:34:31 pm

Foretravel changes things all the time, but here is how a '99 works.

dash air expansion valve

Re: How Dash Air Works - U320

Reply #31 – July 01, 2021, 04:38:29 am

The panel in the last picture is velcro'd on. Pull from the bottom and the top edge is slipped under the top of the dash. Among other things, many self resetting CBs behind it.

Rich

Re: How Dash Air Works - U320

Reply #32 – July 01, 2021, 11:35:52 pm

I just started reading this post and realized I was having some of the same issues with my AC. I am not getting very cold air and have tried charging the system. I had a tech look at it and he said I would have to replace this unit and hoses. (See pictures) This unit is on the drivers side right side of engine. Is he correct and how is this part of the AC?

Re: How Dash Air Works - U320

Reply #33 – July 01, 2021, 11:39:45 pm

That is your A/C drier filter and if the pressure is too high on the highside and too low on the lowside should be replaced. Not the only thing that can cause that but the first thing to replace in trouble shooting.

Re: How Dash Air Works - U320

Reply #34 – July 01, 2021, 11:43:34 pm

Ok do the hoses have to be replaced as well? Do you happen to know the part number for this and if it is a diy project?

Re: How Dash Air Works - U320

Reply #35 – July 02, 2021, 12:14:02 am

They might think that the hoses are frozen to the fittings. If they can be removed I don't know why they would have to be replaced.

Re: How Dash Air Works - U320

Reply #36 – July 02, 2021, 01:10:28 am

Quote from: Rich Bowman – July 01, 2021, 04:38:29 am

The panel in the last picture is velcro'd on. Pull from the bottom and the top edge is slipped under the top of the dash. Among other things, many self resetting CBs behind it.
Rich

Thanks Rich. I did get this panel and the one next to it off...bottom of the dash fully exposed and I still don't see anything that looks like a darn blower! Guess I'm going to have to call the mothership tomorrow.

Re: How Dash Air Works - U320

Reply #37 – July 02, 2021, 05:48:26 am

Quote from: WS6_Keith – June 29, 2021, 04:00:58 pm

I also read in another thread about a "bridge rectifier" that could also cause the fan not to run.
1. Does anyone have a picture that shows the location?
2. Any idea how to test or where to buy a replacement?

Keith,

1. Now that you have the dash apart you can see the bridge rectifiers mounted on the metal air box. they are the little square black things with 4 spade lugs. They will be mounted with a screw through the center hole in each one. They are just above the cube relays (one of these may be your culprit rather than the rectifier) that I can see in this last picture you posted.

2. With a multimeter. They aren't anything but a a fancy diode set. Here is the first video I ran across for a simple explanation testing a bridge rectifier with multimeter - Bing video This is easier than me trying to explain in a long post here.

3. The fans are hid inside the metal boxes that you have exposed. You will need a 1# coffee can for all the screws you are about to remove to get to the fan.

Mike

Re: How Dash Air Works - U320

Reply #38 – July 02, 2021, 09:23:56 am

I would not worry about getting to the fan motor until you have verify that the fan is getting the correct power. As stated above high speed is just going through a relay to give the motor 12-13 volts. I see this relay go bad all the time due to bad loose connections on the relay.

I would also verify your switch even though you said it was new is working correctly.

Re: How Dash Air Works - U320

Reply #39 – July 02, 2021, 10:22:44 am

Quote from: turbojack – July 02, 2021, 09:23:56 am

I would not worry about getting to the fan motor until you have verify that the fan is getting the correct power. As stated above high speed is just going through a relay to give the motor 12-13 volts. I see this relay go bad all the time due to bad loose connections on the relay.

My latest testing seems to show that the fan blows on low all the time. The switch has 3 settings and 3 connections. It looks like the high speed connection has 2 wires going to it. Is this power and the output? What should I see coming out of the switch? I'm guessing it's basically a resistor switch and I'll see 12v on high and lower voltages on medium and low?

Re: How Dash Air Works - U320

Reply #40 – July 02, 2021, 11:58:02 am

Are the bridge rectifiers expensive? If not, perhaps I'll just replace them to be sure...I'm sure they are as old as the coach, so old enough to vote.

Re: How Dash Air Works - U320

Reply #41 – July 02, 2021, 01:50:35 pm

Quote from: WS6_Keith – July 02, 2021, 11:58:02 am

Are the bridge rectifiers expensive?

No, a 50 amp should be ~$5 to $10 they do come in different amp ratings which will vary the cost.

Mike

Re: How Dash Air Works - U320

Reply #42 – July 02, 2021, 02:01:12 pm

Quote from: WS6_Keith – July 02, 2021, 10:22:44 am

My latest testing seems to show that the fan blows on low all the time. The switch has 3 settings and 3 connections. It looks like the high speed connection has 2 wires going to it. Is this power and the output? What should I see coming out of the switch? I'm guessing it's basically a resistor switch and I'll see 12v on high and lower voltages on medium and low?

Possible this is the way it is wired. Check with vm and get back to us. Follow the high speed wire to relay and see if relay is working relay should have 12v going to it and then switch is on high should have 12v going out to Motor

Re: How Dash Air Works - U320

Reply #43 – July 02, 2021, 05:51:35 pm

I will test this stuff this weekend, but also called FT and ordered 5 new rectifiers. $11 each, so that doesn't break the bank. If there's an issue, I'll have the parts next week. If not, I'll have spares.

Re: How Dash Air Works - U320

Reply #44 – July 05, 2021, 12:22:25 pm

I guess I should have looked a bit deeper before just ordering parts. More dash disassembly has revealed no less than 15 of those bridge rectifiers under there. What's also odd is that every video/webpage I've found mentions using all 4 posts to convert AC to DC, but all of these are wired only using the load terminals. I'm not sure what they are doing with only those two terminals in use. There doesn't appear to be any loose wiring in there, and it looks like I'll have to cut apart a few wire ties to separate out the fan switch wires to follow them.

Looking on my schematic, I don't even see these rectifiers shown, or the dash fan speed switch. Maybe my manual is missing a page? I might have to make another call to FT about this tomorrow.

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