Community Forums

ZACFRD · 06-10-2011, 12:37 AM

Can anyone help?? when I run the dash fan ac or heat the air flow only comes out a couple vents. It wont change with the selector to floor or front vents. It only comes out defrost. The switch works i beleive because in off position it shuts off.

H. Miller · 06-10-2011, 07:41 AM

We've been fighting the same battle for two years! Am told that "failure mode" is defrost. Failure of WHAT is the question. 2 different RV service centers can't find the problem so next is a good A/C shop.

Skip426 · 06-10-2011, 09:46 AM

Since there is no info on your type of unit , I'll assume DP, so the first thing to find/check, will be the vacuum pump and test for operation and leaks in the related hoses. The dash vents on most DP's are vacuum controlled and that vac. is supplied by a small electric pump mounted on the outside of the firewall. Test for voltage with the key and A/C controlls on , if the pump runs , check for vac in the resivoir. Usually a plastic canister mounted near by . Hoses will run through the firewall to the dash control, and the to the control pots in various places on the A/C housing. Check everywhere for a disconnected hose or a cut/rub through.
Yes default on most systems is defrost.
The dash control has both, vac and voltage functions.

ZACFRD · 06-10-2011, 10:14 AM

it is a dp. I will check these things this weekend and let you know. Thanks

ZACFRD · 06-10-2011, 11:50 AM

Ok,
I got it changing vents. It was bad connection on air pump. When I turn to AC it blows out defrost though. Is this normal? It would be nice for it to blow out front vents?

hes4all · 06-10-2011, 09:26 PM

I had it happen to me too. Pull out the generator and to the left there is a vacuum pump. Mine got unpluged (Power) when I puller the generator out to service it. Mountain Aire model

Skip426 · 06-10-2011, 10:45 PM

ZACFRD, is all the air flow still coming out the de-frost or are you getting some out the dash vents? Do you get any flow from the dash vents when the A/C is off and you select vent mode? If you have the fan turned off when you select a mode can you hear any of the pots moving the control doors in the dash ? You may have other vac. leaks in the dash, or at the pots; Vac control pots; you should have at least 3 maybe as many as 5. in the A/C system. Some pots if they develop internal leaks may operate slowly or only have enough push/pull to operate when the fan is off. ( No air flowing over the control doors). 90% air flow through the dash vents with 10% to the floor would be what I would consider normal. If the vac. pump was ingesting out side,un-filtered, air it may be weak. Should pull 11 to 14" of vac. If the vac. is low it will slow the whole system down. Maybe time to invest in a Manual Vac. Pump/gauge, for a full system test. Man.pump is also usefull for testing the pots for leak-down. Good luck, let us know how you make out.

ZACFRD · 06-11-2011, 08:14 AM

Ok I have it switching. But it doesnt blow out front with AC. Is it normal to do that???

wa8yxm · 06-11-2011, 12:11 PM

If you are driving a Gasser, Then VACUUM is used to change the port settings, If ther eis a Vacuum leak it defaults to defroster. I might add, the vaccume is normally tapped off the brake booster if you have one, (Before the check valve, that is engine wards of the check valve) so if you have lost air flow control.. You may have a serious safety issue depending on where the break is.

On one car I had, it was the cruise control slave cylinder that was leaking.

Hanker · 06-11-2011, 12:17 PM

Check all the plastic vacuum lines and the fittings. I had a broken fitting connecting three lines together.

lundy · 06-12-2011, 08:56 PM

I, too, have the same problem (air comes out of defroster, only). The unit is on a Ford and is new. When you figure out the problem, let me know. With the number of Ford Chassis MH out there, you would not think that this would be an isolated occurrence and rare.

Lundy

Skip426 · 06-13-2011, 12:51 AM

ZACFRD, Sorry I was away for a few days, By front I assume your refering to the dash vents pointed straight at the driver/passenger seats. On A/C you should be getting almost all the system air flow through these vents . You will have to acess the back of the heater/A/C control and make sure the vac. harness is properly attached. Then trace every vac. tube in the harness to the vac.pots . When you find the pots, make sure the linkage form the pots to the doors is attached and free to move. Then with the key on and the vac. pump running push the buttons on the control one at atime and watch for move ment. If you find a pot that won't move with any button pushed, the pull the vac. supply line push the buttons again the check for vac. in the line. If you don't get vac then you probably have a switch problem or a pinched or leaking tube in the system somewhere. if you have vac. in the tube and the pot won't move then you have an internal problem in the pot. There are two types of pots; vac. applied/spring off. vac . supplied to one end of the pot. and double vac. vac supplied to both ends. The spring return is most common, but if the control buttons don't vent the vac. they are frozen in place. If you can check all your pot and air flow doors I'm sure you'll find your problem. Hope you have room to look around under your dash, a small mirror will help in the tight spots. Keep us posted.

"007" · 06-13-2011, 02:45 PM

Check out this Evans link select your control board type, for how control should work.

lezmark · 06-14-2011, 09:16 AM

I had the same problem with my gasser and once i started poking around it was a very easy fix! FIXED IT FOR $.42!!!! spent a lot of time searching on line and it appears this is not an unusual problem. Somewhere I saw that the hoses connect to a semi round plastic "ball". I remember seeing something like that! Right there in front above the battery was this thingy. I followed one of the lines to find it was almost broken in two! It was a thin hard plastic line that seems to have worn at the firewall. I snipped off an end and took it to the local auto parts store and asked them to match up a vacuum hose that this hard line would fit into. Piece of cake. Since I was on a roll i also asked for 6 inches of another piece of hose that I could use to insert this new hose into as further protection going thru the firewall. Come back and slide the pieces together and everything works just like new! I love it when I can fix things, save money and learn something. I have to believe other others have had or will have this problem and you need to know how easy a fix this can be.