Stumped on Max AC not working

swreeder70 · 09-21-2011, 09:11 AM

I've done a lot of searching and reading on this topic and still have not been able to resolve my issue.

Max AC blows majority of air out the defrost vents is the symptom.

So from what I have gathered, this is most often a vacuum hose problem. So I pulled the dash cover and located the black supply coming from the pump, the blue and green that come from the switch and go into a splitter. Each running to a actuator on the AC unit under the hood.

The lines all appear to be in good shape, no cracks, kinks, bends or splits. The pump is producing pressure (I can feel it) and all other modes work on the HVAC except MAX AC.

Any thoughts on what I might be missing before I have a dealer look at this??

RKL · 09-21-2011, 10:07 AM

I believe you have the classic green hose to the vent damper leaking...when it does it diverts air to the defrost vents...open the front hood and look for a green small hose going to the valve (black) just next to the big black ac/heater box on the fire wall. the hose usually leaks where it connects to a small black rubber hose which goes to the valve.
lots on this forum about the green hose....rkl

wa8yxm · 09-21-2011, 11:10 AM

Does air EVER come out the dash vents? I know cars better than motor homes but on a car the air-conditioning vacuum is normally tapped off at the brake booster check valve, Now, this same tap provides vacuum to the cruise controle vacuum solenoid.

I had a leak in my CC solenoid, this caused a reduction in vacuum in the system so when under acceleraton it would default to DEFROST, which by the way is the Default position (no vacuum)

MEASURE the vacuum on the lines.

Skip426 · 09-21-2011, 12:12 PM

Quote:

Originally Posted by wa8yxm

Does air EVER come out the dash vents? I know cars better than motor homes but on a car the air-conditioning vacuum is normally tapped off at the brake booster check valve, Now, this same tap provides vacuum to the cruise controle vacuum solenoid.

I had a leak in my CC solenoid, this caused a reduction in vacuum in the system so when under acceleraton it would default to DEFROST, which by the way is the Default position (no vacuum)

MEASURE the vacuum on the lines.

To go any further you are going to need a vacuum , pump/ gauge , and a flow chart, from the A/C manufacturer, A wa8yxm, says , defrost is defalt mode, you could be looking at an internal leak in the recirc door servo; mine is under the hood, you can watch it operate; or a plugged distribution passage in the control head. Good quality, pump/gauge about $50. at the parts stores.buying your own could save hundreds at a shop.

swreeder70 · 09-21-2011, 02:26 PM

Thanks for the tips. I was hoping for a quick fix, but doesn't appear to be one. I've traced the hoses end to end, no cracks, boots look good seated into actuators ok and cannot detect any air leaks.

I just picked up the coach three weeks ago (used from a dealer) and discovered the Max AC not working a recent trip. I've got a list of a few other items that need fixed by them, so I will add this for them to check out.

indiana journey · 09-21-2011, 05:08 PM

You are operating the system on vacuum, not pressure. You will not "feel" any air leaks in the system. Vacuum "sucks", not "blows". Most vacuum leaks are hard to find.
Good Luck, Indiana Journey

Paul T · 09-21-2011, 07:11 PM

Identical problem as described on another post and intend to order a new control module switch in an attempt to correct it. Just completed 7400 mile trip without a proper place to have parts sent. Now home, its one of the “little things” that needs done before next blast off.
Search the Workhorse Chassis forum for discussion and part number for the control valve as it appears we are not Lone Rangers attempting to solve this problem or try http://www.irv2.com/forums/f22/chassis-air-cond-vacuum-lines-99384.html

Paul T · 10-13-2011, 06:37 PM

New control switch installed and Max AC selection is now working properly. Pictures of switch and connections posted on the Workhorse Chassis forum at http://www.irv2.com/forums/f22/chass...tml#post982923

Hikerdogs · 10-13-2011, 07:32 PM

Quote:

Originally Posted by swreeder70

I've done a lot of searching and reading on this topic and still have not been able to resolve my issue.

Max AC blows majority of air out the defrost vents is the symptom.

So from what I have gathered, this is most often a vacuum hose problem. So I pulled the dash cover and located the black supply coming from the pump, the blue and green that come from the switch and go into a splitter. Each running to a actuator on the AC unit under the hood.

The lines all appear to be in good shape, no cracks, kinks, bends or splits. The pump is producing pressure (I can feel it) and all other modes work on the HVAC except MAX AC.

Any thoughts on what I might be missing before I have a dealer look at this??

You didn't mention what chassis your coach is built on, or what year it is. If it's built on a Ford chassis. Air going to the defroster outlets is the default position if the system looses or fails to produce sufficient vacuum. A leak in any line or component in the system will result in the problem you describe. It's common for the lines going to the under hood vacuum canister to become partially disconnected or damaged when servicing the engine.

To be sure you have sufficient vacuum available to run the system open the hood and locate the vacuum canister. It should be a round ball in the center (left to right) above the hood opening. There should be 2 lines attached. If either of the lines are leaking or the check valve has failed it could cause the problem you are experiencing. The canister has a 1 way valve that doesn't allow it to loose vacuum from the source line port.

Start the engine and remove the lines 1 at a time. It should be obvious which one is the source. If it isn't remove the engine cover and trace the line fron the canister to the engine. It's possible it's become disconnected or damaged enough that it can't supply enough vacuum to run the system. (In most cases the engine computer will compensate for a small vacum leak. You will likely not notice any engine performance issues.)

If the lines are OK disconnect the one going to the heating system with the engine running. You should be able hear the leak and feel the vacuum when you put your finger over the port. If you can't hear or feel the leak either the lines are reversed or the valve has failed.

Once these potential sources of the problem are eliminated you can move to the heater controls and vacuum operated valves.

Paul T · 10-14-2011, 07:35 AM

Good description of a thorough trouble shooting technique Hikerdogs.
It describes pretty much to what I went through before changing out the control switch.
If I’m not mistaken I think swreeder70 said in another post that he could hear an air leak near the selector valve when selecting Max AC. That was also my situation also but I was very reluctant to get into changing the control switch. Like I said though, it wasn’t an easy task manipulating that stuff blindly and I would put it off for another several months if it was on my to do list now. Any of the other faults would have been easier to fix.
The difference between Max AC and regular AC in my coach is not extremely significant. I got through my 8000 miles over 6 weeks this summer without Max AC but just don’t like things that don’t work like they should.

swreeder70 · 10-14-2011, 08:25 AM

Update on my situation as well:

My dealer did a quick check and by using a pressure tester, they were able to find that there was a leak in the blue line. They basically tested it for free, found where the leak was. A rodent chewed off about a 6" chunk of the blue line under the dash (well hidden from view). Since it was rodent damage, it was going to cost me an hour of labor to have them fix it, so I opted out and they didn't charge me for the troubleshooting.

So my question to all is I have a 6" section of blue tubing that was chewed out that I need to replace. Is there a way to splice in a new section of tube or do I have to replace it all (which seems like a difficult job).

DAN L · 10-15-2011, 02:56 AM

Quote:

Originally Posted by swreeder70

Update on my situation as well:

My dealer did a quick check and by using a pressure tester, they were able to find that there was a leak in the blue line. They basically tested it for free, found where the leak was. A rodent chewed off about a 6" chunk of the blue line under the dash (well hidden from view). Since it was rodent damage, it was going to cost me an hour of labor to have them fix it, so I opted out and they didn't charge me for the troubleshooting.

So my question to all is I have a 6" section of blue tubing that was chewed out that I need to replace. Is there a way to splice in a new section of tube or do I have to replace it all (which seems like a difficult job).

i spliced in sections of 3/32'' or 1/8'' rubber vacuum tubing to fix my vacuum lines.

i don't remember which size for sure.

Paul T · 03-24-2012, 12:53 PM

I had previously posted, (erroneously), that replacing the swich fixed my problem.
I learned later that it had not but only posted that info on the Workhorse forum. See posting and picture of the leaking line at http://www.irv2.com/forums/f22/chass...ml#post1123724
I don't know if that blue line belongs to Winny or Workhourse but bet some of you with gassers may encounter the same problem near year 4 or 5 of ownership.

DAN L · 03-24-2012, 04:25 PM

Quote:

Originally Posted by Paul T

I had previously posted, (erroneously), that replacing the swich fixed my problem.
I learned later that it had not but only posted that info on the Workhorse forum. See posting and picture of the leaking line at http://www.irv2.com/forums/f22/chass...ml#post1123724
I don't know if that blue line belongs to Winny or Workhourse but bet some of you with gassers may encounter the same problem near year 4 or 5 of ownership.

on my moho, the blue vacuum line leaving the selector switch tees about 10'' from the switch. the green line to the heater temperature control valve starts there. the tee doesn't look like a T, it is actually a black rubber connector that acts as a splitter.

Paul T · 03-25-2012, 08:56 AM

DAN L – The configuration, (Blue line Ts to another Blue and Green,) underneath the dash about 10 inches from the actuator switch as you describe is exactly the same as mine. In trouble shooting I first tried blowing into the actuator end, (in engine compartment by heat valve), of the green line and had normal resistance. When I detached the blue line from its actuator and blew into it I could hear air escaping someplace. After unwinding the blue line, (passenger side in engine compartment), I could see hear it louder and see where the line had been abraded along nearly 5 inches of its length due to rubbing against the lines it was wrapped around. Hard to see but easy to hear when engine off.