BAC Forum
General Boards => Technical Support => Topic started by: Dick Simonis on August 15, 2016, 04:32:14 PM
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All of a sudden my dash air stopped blowing cold. Like a fool I didn't have it checked while I was at BCS for service and suspect I am low on freon. In a bit I'll fire it up and make sure the compressor is running but, assuming it's OK, I will run into town and pick up a recharge kit. My question is how many bottles would I need to fill it back up?
Thanks for any insight.
Dick
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Dick - Have you found the valve where the refrigerant is introduced into the dash air conditioner system? I have not looked yet but plan on soon doing what you're doing. I know many messages here say it's over the generator between the dash and front end on my year coach.
Don't I remember that Bill Sprague wrote about how much refrigerant these systems have?
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David, we did find the low port right where you noted it would be. I am picking up new hose with high port this afternoon as when someone charged system before they evidently changed out a hose that did not have a port on it.
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I know there is a port because the sales lot had charged the dash air just before we purchased the coach four years ago. I just do not know where it is yet. I didn't think to ask where the port is located. I had enough going on with the "new owner's school" that morning.
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Well the problem isn't as simple as I had hoped. It was easy to find the ports as they are right at the compressor but the compressor clutch isn't engaging. The AC light is on suggesting power is being supplied but no mas. I didn't find any relay or CB for the compressor but there is a connection on TB2 for the clutch but I haven't yet figured out if that is power supply to the AC control panel or power from the panel to the clutch. There isn't any breaker in the DC power panel for the compressor and my wiring diagram is for a 2003 Marquis which is different then mine.
Time to dig deeper but if anyone has any insight that would narrow the search suggestions would be appreciated.
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When the system is very low on Freon, the low pressure switch will keep the compressor from starting. Charging the system should eventually trip the low pressure switch and then pressure readings can be taken.
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Thanks Larry that makes sense. So as one puts in freon with the system operating eventually the compressor kicks on??
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Dick, the clutch not engaging would suggest that the freon is low, meaning that there is a leak in your system. Not enough pressure to engage clutch. A good set of gauges to monitor low and high side pressures will lead you in right direction. When recharging system, put dye in system to locate leak easier. Most motorhomes need recharging yearly. Hope this helps.
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Dick,
As long as you have some pressure then you can add slowly to the low side with the can in the upright position until the compressor kicks on. You should see the pressure slowly rise on the gauge. If the pressure is above, or rises above approximately 30 lbs while adding R134A and the compressor is not on it is likely that you have some electrical issue that will have to be sorted out.
If you are using a standard set of gauges, purge the yellow hose at the gauge by loosening the coupling while the can is upside down, and the can valve slightly open until you see 134A vapor emerge and then tighten the hose fitting. That purges air so that it is not pushed into the RV system. As far as the shorter hose recharge kits, the short hose is not much to worry about air wise. Try and get one with numbers on the gauge. If your compressor is not running due to low pressure I would have on hand 36 to 48 oz or 3-4 of the standard size 12oz cans.
This article is a good overview.
http://www.rvtechmag.com/tech/51_r134.php
The fully charged pressure with low and high sides equalized (1 hour after system is turned off or next day is better to get the temperatures of the system to a common ambient temp) is in this article. Fully charged is the pressure in the table for your current ambient as measured at the condenser face. Hope this helps.
Later Ed
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I just had my dash air system completely replaced with all new parts in December at Ringpower CAT in Brooksville Florida and had cold air for two weeks. Hasn't been cold since.
I just spoke to the service manager there in July and he said that they could look for a leak by the hourly labor rate.....I don't think that's going to happen any time soon. I will buy my own sniffer on Amazon and accomplish the same thing for nothing.
About 3-4 12oz cans should be the right amount to service it.
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OK, ran into town and bought a fancy recharge pack plus on extra bottle. Hooked it up and the pressure on the L side indicates 100 psi so that isn't doing the trick. Now it back to finding a way to get the compressor to run but need to find where the power comes from. There is a single wire going into the clutch which a figure must be the +12V but no obvious connector. Guess I could cut the wire and jumper it to a 12V source and see if the clutch engages. There must be a fuse or ??? someplace but there isn't anything obvious. Do these coaches have fuses in some hidden location??
3:15 PM, to close to cocktail time to work any longer so it time to mull it over.
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Your magnum chassis manual has the amount of freon needed to refill. Check the fittings on the compressor for oily substance. Tighten those fittings often as they are aluminum. If the hoses leak up front or at the compressor it should be obvious.
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Dick,
That is a +12V wire to turn the clutch on. There is a pressure switch and probably a relay that controls the clutch. I would check the labeling in the front electrical bay and see if there is a breaker labeled air cond. If you manually fire up the clutch with the engine running, do not do it for longer then is needed to test it. If the condenser fans up front are not on the pressure will be very high. Those fans cooling the condenser keep the pressure under control. Your 100lbs would be a correct equalized charge pressure level for an 88 degree ambient. This does not have to be exact but close is good..
Later Ed
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Dick,
There are two common locations where the 12 volt supply to the compressor are commonly lost. The first and most common one is the trinary switch that is located in the high side, usually near the dryer. The other location is the compressor control switch that is located in the master HVAC control panel in your dash.
Gerald
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Dick,
If the trinary switch Gerald pointed you to is bad, that is usually replaceable with pressure in the system. It should have a schrader valve in the seat. It will leak some while the switch is depressing the valve but should stop at some point while unscrewing. I have only replaced two of these in different vehicles and both were schrader valved. Would hope yours is similar.
Later Ed
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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.
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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
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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.
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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
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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
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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
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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.
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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
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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.
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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
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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.
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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.
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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
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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.
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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
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Thanks Gerald. I'm going to have it looked at by a shop in Idaho Falls but he advised me that the parts might not be readily available from local sources.
I am curious though about this trinary valve. Way back when the R-12 systems always had separate high and low pressure switches. How can one switch monitor both the high and low side?? In which line is it installed? Thanks for any enlightenment.
Dick
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Dick,
I replaced the expansion valve and the dryer on my coach last year and Fleet Pride truck parts in Phoenix had both of them in stock. They were fairly common truck parts.
The trinary switch is in the high side at or near the dryer. It does not monitor the high and low side, but it monitors the high and low pressure ranges in the liquid line (high pressure line after the condenser). It prevents the compressor from engaging if the high side pressure is too low (discharged system) to prevent compressor damage, and it turns on the condenser fan when the pressure rises sufficiently to cool the high pressure gas so it will condense into a high pressure liquid for the expansion valve.
Gerald