Dash Air Recharge

[Doug Allman]

Finally have all the parts in place, the system purged and tested for leaks with nitrogen. Started to install refrigerant and pressure starts to rise. The fan on the condenser does not turn on.
We have checked the relay, the 20a fuse and all are good. Use 12v to check and the fan runs fine. The schematic shows what I believe is the symbol for
a switch coming off of 85 on the relay.
Where do we find the switch?  At the end of the symbol which I believe is the switch is  C9-10. Is this a wire number? or does it have some other meaning.
My A/c guy said to ask if we could just put in a temperature switch on the 85 terminal and forget about replacing the old switch. Any help would certainly be welcome.

[Gerald Farris]

Doug,
Your condenser fan is powered through the trinary switch that is located in the high pressure line, usually on or near the dryer. The fan control is designed to turn the fan on only when there is high pressure in the high side line. Therefore, it will not come on unless the compressor is running with at least a partial charge.

Gerald 

[Doug Allman]

Finally have dash air working!
Over a month and a half we replaced all the items, compressor, dryer, TXV valve, new hose with high pressure port, all new O rings and tested all other items for workability. Numerous wrong items shipped and returned but finally got all needed correct. At that point we charged system with refrigerant and condensor fan would not come on.
Check switch on dryer and with testing we found which of four wires was low temp switch. Corrected connections and still no fan. (why there is 4 wires we do not know because only two wires, verified 4 times by 3 persons, come from wire loom to dryer location.)
Per Gerald we ran a single wire to the back of the coach to the compressor, piggy backed on compressor wire. Purchased a relay kit (which will be installed in the electrical bay at drivers front corner of coach) and connected new wire to Switch side power contact. Took condensor fan power wire, cut and connected to power side contact of relay. Then ran two wires to condensor fan under electrical bay, one ground and other power from contacts on relay.
Turned on key to coach and a/c power button on dash and fan came on. Started coach, compressor came on and fan also. We then started to get some cooling from a/c. Added more refrigerant and monitored temp coming out dash air ducts. When temperature achieved 45 degrees we stopped adding coolant at 4lbs 4oz.
We believe we have a low temp trinary switch in the dryer that will shut off compressor if it senses low pressure. We also know that if the cooling temperatures do not stay cool that we need to get a recharge of refrigerant and keep a/c off until we do to protect compressor from burning out if the low pressure switch is actually not working. We fully believe that is what burnt out the last compressor, a non working trinary low pressure switch, but we have no way to verify that for certain.
It has been a saga that I and my a/c man have lost a lot of sleep over BUT we finally got it working and that is worth smiling over.
Without Gerald it would not have happened as we were at our knowledge and wits end. We were actually way over our heads in the knowledge side.
We reviewed the wiring schematic numerous times and where some of these locations are on the coach from the notations on the drawings is a total mystery in itself.
THANKS again to Gerald for the $14.00 relay kit fix.

[Dick Simonis]

OK, a little update on my issue.

I wanted to find out if the compressor was the problem so I scrapped a bit of insulation from the wire and ran a jumper wire direct to the battery and found the clutch would lock up.  Next I started the engine and set the AC on max than put the jumper back on.  AC worked like a champ and immediately delivered ice cold air.  Disconnected the jumper and the clutch stayed engaged so I hooked up my recharge kit and the pressure gage indicated ~13 psi on the low side.  Went through my original Freon bottle and the extra which brought the pressure up to just under 20 and the ac was working just fiine so I thought I had it whipped.

Shut the AC down and went to town for a couple more bottles but when I started it back up...same issue the clutch would not engage.  Hit the wire with my jumper and back in operation and stayed there even after removing the jumper.  Added one more bottle and the clutch disengaged but the pressure was ~25. 

Why the compressor will not run without a jump seems a little odd but if I do have a faulty switch I could almost see that as a cause.  I starting looking for a switch but there are a lot of them available.  If anyone has a make and PN it would be greatly appreciate.  I'm not sure I can physically get under the cap to change it but having the correct one in hand would beneficial if I can find someone to do that task

Thanks for all the help so far.

Dick

[Edward Buker]

Dick,

I do not have the PN for the trinary switch but BCS parts should. You need to check the ambient temp vs the pressure once the low side and high side has equalized. There is a table in a link I posted recently. If the pressure is still low for the current ambient temp then add enough to get the proper pressure. The jump start can be needed to exceed the low pressure threshold, typically around 30lbs to have the compressor function. The compressor changing the pressure at the trinary may be enough to have it function if it is balky. Once you know that the static pressure is correct, which means the charge level is correct, and the trinary is still not functioning then you need to change it.

There is one other possibility and that is a voltage drop in the wiring or the trinary switch that makes the initial clutch engagement not work, but once you enable that manually with 12V at the compressor the voltage and current from the trinary is enough to keep it engaged. Some voltage measurements of what the trinary is providing to the clutch should help sort this out.

Later Ed

[Edward Buker]

You May Want To Print This As A Reference....

I wanted to post this table and be sure that it made sense to everyone attempting to add R134A charge, either professionally or otherwise. It lets you know if your coach has been properly charged regardless of who does it.

Unless you deplete all the refrigerant, go through a vacuum pump down, and do a known weighted charge of R134A for your specific system/vehicle, this first table is the only accurate means to know if your final charge is correct.

The pressure in an air system is a dynamic number that changes with the ambient temperature. On a 75 degree day your system's equalized pressure (system at rest high side and low side pressure are the same) should be 79 PSI. If the day is 85 degrees the pressure jumps up to 95 PSI. This is the temperature of the R134A gas in your system that is the reference. An IR gun reading underneath the coach on the condenser face, after the coach has been sitting without being run, is a good way to get a temperature estimate before you start charging or to see if you even need to add to the current charge. If no IR gun use the outside ambient temp. These are the values in the table below that you are seeking to achieve for a proper charge at a given ambient. These values are the only proper charge values for any R134A system, car, RV, bus, etc. Even a weighted charge is seeking to deliver a charge resulting in these values. You can estimate the numbers in between that are not listed.

When you have added R134A, once the coach is cooled down and has been sitting, you can check and see if your resultant charge level is correct. Within a few pounds is OK, it doesn't need to be exact, if low I will add a little, if a little high I quit. Higher pressures stress the system and do not improve cooling.

Refrigerant R134a Temperature-Pressure Table

 Temp (F)     134a Pressure(Psi)   
 
  40.0      35.1
  45.0      40.1
  50.0      45.5
  55.0      51.2
  60.0      57.4
  65.0      64.1
  70.0      71.1
  75.0      78.7
  80.0      86.7
  85.0      95.3
  90.0    104.3
  95.0    114.0
100.0    124.2
105.0    135.0
110.0    146.4

Now the question is, how do I do the charge using the high and low pressure values, while the coach is running, with the air system on. For a given ambient temperature you use the approximate values in this table and then stop adding refrigerant. Depending on your gauge set you may only have low side readings which is fine. These values assume that the condenser fans are on and that the interior fan is full on blowing air that is cooled passing through the evaporator.

This method gets you close, you can check where you are using the first table when the coach has fully cooled down, pressures have equalized, and the system has reached an ambient Temp.

Ambient F      Low Side Pressure (Psi)    High Side Pressure(Psi)
   
    65                      25-35                           135-155
    70                      35-40                           145-160
    75                      35-45                           150-170
    80                      40-50                           175-210
    85                      45-55                           225-250
    90                      45-55                           250-270
    95                      50-55                           275-300
   100                     50-55                           315-325

I have the pressures vs temp from this table info that I use, on a plastic plaque inside the engine compartment, which has been a handy guide while doing the charge. Post them handily wherever the ports are where you do the charge on your coach, mine are at the compressor. Once my charge level is correct I usually wait until I notice that the cooling seems is a little weak and then I use the first table to see where I am and then peak it using the second table. If this has been a bit of a mystery to some, I hope this helps.

As always with air conditioning charging, safety glasses, add R134A slowly only to the low side, add gas with the can upright, if the can is upside down you are adding liquid that can damage your compressor, getting hoses or clothes caught in a moving belt can make for a very bad day....

Later Ed

[Dick Simonis]

Ed, thanks for the very helpful information.  I just ordered a set of gauges so  can have a better look at what is actually going on rather than just the low side pressure gage that came with the recharge kit.  Hopefully they will arrive today and I can fuss with it a bit tomorrow.....still to hot here to play golf.

[Edward Buker]

Dick,

With that gauge set you will have access to the high side pressure as well as the low. The yellow is the feed hose and whichever hose valve handle you open, red or blues side, will connect to the yellow feed hose.

The hazard is having the compressor on and cracking the red side valve which can then send high side system pressure back into the can at up to 250+psi. Not sure what the burst strength of the can is. The high and low gauges work with both of those valves closed so you only open the blue side to add refrigerant.

The only time you need to open the valve for the red side on the manifold is when you are using a vacuum pump to evacuate the system. It might even be safest to remove that handle on the red side and store it in the box. Whatever works for you so that if your adding R134A you do not inadvertently open the red side valve... because we do not do this very often it is easy to forget...the mind is a terrible thing when confusion decides to make a visit  :-)

Later Ed

[Dick Simonis]

Thanks for the reminder Ed.  It's been awhile since I worked on refrigeration units.  Back when we lived on a sailboat I did all my own work but that's back when you could buy tanks of R-12 at Price Club so yeh, been awhile and memory fades.

[Edward Buker]

Dick,

It is always hard to know the skill level of the person with the query. I probably tend to put more   information then may be needed in a post. There are 779 views on this one already with viewer varying skill levels, so I guess it is a good practice to consider the broader audience. Hate to have someone get hurt.

I used to have a Ranger 29, way back when, on Lake Champlain in VT. Just an ice box, an Atomic 4, some sails, and some wind. You probably had an alcohol stove or two in your day. I referred to those as the eyebrow blow torch :-) On a sailboat it was good if you could service everything in a pinch, no help to call on when high adventure strikes...

Later Ed

[Dick Simonis]

No problem Ed, and your info is always spot on.  I totally agree that responses are best served to a larger audience than the original post to achieve maximum benefit.

We lived on a 50' ketch in San Diego for almost 10 years plying the southern coastal pacific waters and there is always a "sinking" feeling that accompanies a failure  many miles out to sea.  Being able to resolve issues was pretty useful.  MacGyver should have been a sailor.

[Dick Simonis]

My gauges arrived yesterday so I'm back on the job but it looks like I may have some other problems.

Pressure reading after sitting for a couple of days were 70 psi Low side and 75 psi high side.
With engine running 20 psi Low and slowly rising to 425 High at 65F ambient.  Not good.

On the upside the compressor started with no issues and the condenser fan is running.

I now suspect that my expansion valve or fixed orifice (not sure what this system uses) or the filter/dryer is causing a high side restriction.  Either way I may have reached the limit of my abilities to correct in the field.  There is also a possibility that my earlier work using just the single gauge on the recharge canister may have contributed to the problem by thinking the system was low on Freon while it may not have been and consequently over charging the system.  Also of note I did not see the low side pressure readings change as the system cooled down but I'm unclear on how much it should change with a properly operating expansion valve.

Last is that again the compressor clutch has once again refused to engage without a jump from the battery and than it stays engaged and the condenser fan runs.  Sequence of events...turn on the AC system (without the engine running) no clutch or fan,  jump the compressor wire from the battery....clutch engages and fan starts.  Remove jumper and all is well.  This one is baffling.  I must be back-feeding something that locks in when I use the jumper...relay somewhere???

Thanks again for any advice.

[Edward Buker]

Dick,

After sitting that long the high and low side should have equalized completely, that and the high side pressure going so high would say to me that you have a restriction somewhere. When you saw the 70 to 75 lbs high and low side nearly equalized was that at 65 degrees? That is about right for 75 degrees. Check temp vs pressure when all is cool and if you are over charged bleed a little bit off until it is right. Do that by closing off the can valve on the yellow line and opening one of the yellow hose threaded fitting to bleed some off using the low side valve to regulate it.

With the compressor running your high side is way too high and the low side is too low. The clutch should kick with the 75lbs equalized pressure but would kick off quickly when the low side dipped below about 30lbs. If it never starts then the trinary switch still looks bad.

Maybe a bad expansion valve can cause this, Gerald has more experience with those and can weigh in.
This is a very good diagnosis chart from Sanden. Seems they lean toward something being plugged up, usually a screen built into a component. The usual culprits plugging the screen are the receiver dryer desiccant containment rupturing or debris from a failed or failing compressor.

http://www.sanden.com/objects/SANDEN_SYSTEM_DIAGNOSIS_CHART.pdf

This may be beyond what you bargain for or are equipped to work on but sorting out what is wrong may help you decide that. Get the charge right and see what you have, you can get that far and having the pressures lower even if bad is safer and not as hard on your components. One piece in the diagnostic chart talks about frosting where the restriction might be, may be worth a look at the desiccant cartridge. Hope this helps.

Later Ed

[Dick Simonis]

Thanks Ed, I've been keeping an eye on it and now it seems spot at 90F.....105 psi both sides.  At this point there is no more I can do myself but at least I'll know what to talk about when I find a shop.  Of course we're in Lebanon, OR and scheduled to leave next week so finding local talent that can get us in and also with a facility large enough to maneuver the MH has been an exercise in futility.

I tried to get part numbers from Mike at BCS but all he has is the BCS P/N so that didn't help.

When we get to Idaho Falls next month I might have some success at the RV dealerships and I'll have time while Pat is doing Grandmother things.

One thing I will add for future reference is that the single gauge recharge kits should be used with caution.  With no ability to see the high side pressures one could get into a peck of trouble just adding Freon if there is a restriction problem like I have.  Real easy to overcharge.

Thanks to everyone for the help.

[Gerald Farris]

Dick,
I can not tell you what your problem is without personally checking the A/C system, but your clutch engagement issue sounds like a bad trinary switch, and your cooling issue when the compressor is running is either a bad high side hose that has a disintegrating lining causing a restriction or a bad expansion valve with the highest probability being the expansion valve. If you change the expansion valve, it is usually a good idea to replace the dryer also.

Gerald