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Topic: A/C Compressor on during the Defrost Mode? (Read 2555 times) previous topic - next topic

A/C Compressor on during the Defrost Mode?

While reading J.D.'s response to the light circuit issue, reawakens me to convert the a/c compressor to be on when in the defroster position also.  Just wonder if anyone has worked this out to a simple fix.
Know this issue has been mentioned much earlier, but never had the time to address it, so now I guess it is time to break out the drawings and have a go at it.  Just hoping someone else had already done it for me/us.  :)
Have been lead to beleive MOT shop makes this change, should kick my own butt for not having them do it last month when I was there.  :(
Many Thanks

Re: A/C Compressor on during the Defrost Mode?

Reply #1 –
Dave, Having the AC on during defrost is useful and the way most vehicles are set up.  The cold evaporator removes moisture from the air going to the defrost outlets and that way the WS does not get foggy.  I would leave well enough alone, the last thing you need is a fogged WS in cold weather when you are driving.  I have driven into a dip where air was extremely cold and had WS fog immediately due to temp difference.  YMMV
Gary B

Re: A/C Compressor on during the Defrost Mode?

Reply #2 –
Gary, Yup, that is correct, in my case the a/c compressor does not turn on when you select the defrost mode.  Yes the winders sure do fog up quick is some conditions.
I find the best (so far) is to run the a/c at max, high speed fan, and the roof a/c units, that will pull the condensation from the front winders.
Why I would like to have a simple way to make the a/c clutch pickup when in defrost mode.  Could always add a SPDT switch and make her run, but prefer a moe better way. ;D

Re: A/C Compressor on during the Defrost Mode?

Reply #3 –
Quote from: Dave M –
Gary, Yup, that is correct, in my case the a/c compressor does not turn on when you select the defrost mode. 
?? On our OLD (compared to yours  ;) ) coach, the A/C compressor is switched on with the defrost mode. I just went out and checked the wiring with a my eyeballs and a voltmeter. The wire from the "Defrost" position of the fan control switch and the wire from the A/C switch are joined a few inches from the switches. It looks like OEM work.

If your coach is not wired that way, I would expect modification would be easy. Find the "output" side of the A/C switch on the dash. Find the "output" of the "Defrost" switch. Wire a jumper between the two. Your results may vary if your NEW-fangled switches are different from my OLD switches.

If you will pay my round trip expenses to travel to your location, I'll help you fix your wiring for free. I will even supply the wire and two taps. :P
J D Stevens
1997 U295 CAI 36' Build #5085
2002 Subaru Outback
Motorcade 16869
Bellville, TX

Re: A/C Compressor on during the Defrost Mode?

Reply #4 –
JD, for sure, 1st, in my 01 model, for some reason the a/c clutch coil wire is not connected to operate in the defrost mode, I have no idea how your unit is wired,  am glad for you that it is.
Yes, from a technical point, it is a extremely simple matter, I was hoping maybe someone had worked it out and was willing to splain it in simple english.
I know my unit is not alone in this feature or lack of feature. Maybe someone knows why ?
See I need to get out the drawings for the HVAC system and have a look see.
Thanks

Re: A/C Compressor on during the Defrost Mode?

Reply #5 –
Dave,

Do you have a switch dedicated to turning A/C On/Off? Is there is switch for directing air to the Floor/Dash/Defrost? Are the backs of the switches accessible?

If the answers are all, "Yes," we can do the project with two taps and one piece of wire. All modifications would be right behind the dashboard.
J D Stevens
1997 U295 CAI 36' Build #5085
2002 Subaru Outback
Motorcade 16869
Bellville, TX

Re: A/C Compressor on during the Defrost Mode?

Reply #6 –
No switch, just a rotable selector max air, air, dash, up, down, deforst type selections,
NO A/C ON SWITCH,
Have  not taken off the back of dash to look for this switch assy.
The current draw is very light, as the control wire is just to pull up the ice cube relays under the bed to the clutch and condenser fan, so that should not be a problem either.
Hoping FT drawings give wire#, that would sure be sweet.

Re: A/C Compressor on during the Defrost Mode?

Reply #7 –
Quote from: Dave M –
..........................Yes, from a technical point, it is a extremely simple matter, I was hoping maybe someone had worked it out and was willing to splain it in simple english.
I know my unit is not alone in this feature or lack of feature. Maybe someone knows why ?..............................................
Dave,
My design is like JD's..............Defroster on = A/C Compressor enabled..............clutch cycles on the refrigerant switches (with my AC switch in either the ON, or the OFF positions).
I have had several compressor failures, mostly driven by a minute refrigerant leak that I (and a dozen service centers from FT to Carrier) could never find and permanently correct.
First two failures were handled under FT Warranty, third I footed the bill, fourth one I was so frustrated, I took the drive belt off and abandoned the whole system in place.  Now I just run the generator and the roof air or the propane furnace, occasionally supplemented by a dash fan, when needed.
FT and Cummins have both told me that the BIG windshields lead to most owners running in defroster mode all of the time in order to stir hot air (in hot going) and cold air (in cold going).  So, for the typical owners, the little engine driven AC system, designed to just defrost a truck cab small windshield (and then be turned off), was running constantly, contributing to the relatively short compressor lifetime.
My guess would be that in later years, to conserve on AC Compressor run time and the number of operating cycles, FT wired the Compressor to run only when the AC Switch is on and the Defroster switch is on.
Make sense?
FWIW
Neal

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Neal (& Brenda) Pillsbury
'02 U320 SPEC, 4200, DGFE, Build #5984
'04 Gold Wing
'07 Featherlite 24'
'14 Jeep Grand Cherokee Summit
MC #14494
Exeter, NH & LaBelle FL
Quality makes the Heart Soar long after Price is Forgotten

Re: A/C Compressor on during the Defrost Mode?

Reply #8 –
Neal,
Sure does, I do not have a leak in the system, after 4 years use, the freon is still at spec'd pressures, I did lose the condenser fan this summer, FOT had the exact replacement.

I would guess you are correct on the reason they changed the wiring and one reason I might simply add a SPST or even a SPDT to control the clutch and condenser fan, This would provide a normal position and a compressor on position, could use a DPDT and have a little LED to remind me of position.

When I get a little time, I will go through the manual, hoping the wires have # on them.

The reason I would like the choice SPDT, if the condensation gets ahead of the dash air, can have a choice between dry air defroster or normal defroster.

 I did have a close situation from condensation once when the windshield got covered up while I was driving, I had to use a towl and keep swating at the glass to keep a hole to find a safe place to pullover. I normally travel alone, no fun fighting the condensation issue alone.
Thanks

Re: A/C Compressor on during the Defrost Mode?

Reply #9 –
We had MOT install 2 fans near the top of the windshield of our 2001 U270 about 3 years ago. I'm glad we did this. It doesn't solve the problem completely but works best when they are turned on just as the windshield starts to fog.

Robert
Rob & Di
2001 U270 34'

Re: A/C Compressor on during the Defrost Mode?

Reply #10 –
One reason for the engine driven A/C to fail is lack of use in most coaches.  After years of hassles I finally got a shop to replace the expansion valve and do the proper job to fix the system in Forrest.  The shop owner said that his dad's Foretravel A/C has never failed and he has owned two Foretravels in 30 years.  His only admonishment was to run the A/C as often as you can.  And, during storage (if applicable) excercise the coach and A/C once a month as recommended in this forum many times in the past.  Dry gaskets are the most common failures and particularly in the compressor.
 
So, run that A/C often and exercise the coach once a month including the A/C and yours will last as long as a car's A/C.
Peter & Beth Martin
No Forrest? What have you done?
MC# 15890 until Dec 2016; FMCA #F329677
Cincinnati, OH

Re: A/C Compressor on during the Defrost Mode?

Reply #11 –
Thanks to James T and Mark H, I now have the wiring diagrams for my build #,  a/c, heat, vac, etc, most amazing amount of relays, vaccum modules and bridge rectifiers, its gonna be fun.  ;D 
 Thanks all

Re: A/C Compressor on during the Defrost Mode?

Reply #12 –
Per James T. This is the HVAC setup on my build number and I guess some later, no idea when it started.
Not sure where all of it is located, so I am in for a nother learning experience  :o
Have a look and you will get the picture. ;D

Re: A/C Compressor on during the Defrost Mode?

Reply #13 –
Quote from: Dave M –
Per James T. This is the HVAC setup on my build number and I guess some later, no idea when it started.

Interesting - I see a "6021, 6033-" down in the drawing's title block.  Would lead me to think build 6021, and then other U320's starting with build 6033.  Although I could definitely be wrong in my interpretation, since yours is 5903.

-M
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

2000 U320 36' non-slide / WildEBeest Rescue
2003 U320

Re: A/C Compressor on during the Defrost Mode?

Reply #14 –
Quote from: Dave M –
Per James T. This is the HVAC setup on my build number and I guess some later, no idea when it started.
Not sure where all of it is located, so I am in for a nother learning experience  :o
Have a look and you will get the picture. ;D
Arrrrgh! As soon as I saw separate controls for driver and passenger, I figured there was no hope of getting it to work just right. I have had a couple of "luxury" cars with separate controls. The HVAC in those vehicles never seemed to work as well as the simple systems.  >:D

Get Stoltz to help you install fans for the windshield.  ;D  Or go with your plan to "hot wire" the A/C compressor with a switch.
J D Stevens
1997 U295 CAI 36' Build #5085
2002 Subaru Outback
Motorcade 16869
Bellville, TX
 

Re: A/C Compressor on during the Defrost Mode?

Reply #15 –
Actually, Mark sent a few also, Seems to be a little different, showing a computer to control all the parts.

Am leaning  toward the simple DPDT switch with a lil LED to remind me when it is on bypass, If I can locate the wire that runs to the rear for clutch and condenser fan, I will make the simple change, Amen etc.

Also think will settle on the goofy avatar, it seems to be a suitable description.  :)