Dash AC Issues Round 2

[Dick Simonis]

I've been fighting the dash AC issues for a couple of months now and so far without any success.  I had the trinary switch replaced in Idaho Falls but still no power to the compressor and condenser fan without applying power directly to the compressor clutch terminal in the electrical bay.  This is coupled with what appears to be a higher than normal high side pressure....slowly approaching 450 psig at 90 F.  Unless I can figure out if there is a common denominator that that can cause both these symptoms they will have to be approached as unrelated issues.  Later this week Fred Brooks is going to help me and the first step will be to drop the control head and see if we're getting power in and out.

When I bought the trinary switch from BCS I also ordered a new expansion valve but the one the shipped is a bit strange and not one I've seem before so if anyone could tell me what the extra capillary tube is used for it would be greatly appreciated.

[Doug Allman]

Dick, That looks exactly like the one we just replaced on our 2004 Marquis. One of the capillary tubes is wrapped around one of the hoses metal ends and then encapsulated with insulation as it is to sense the cooling passing by (that may not be a very technical explanation). Gerald could definitely help you here.

The dryer/accumulator we had to order 3 times to get the right one that had the port to screw the wires on to that was the trinary switch. Got one out of Texas for around $21.00 and it was exact replacement for what was on coach.

We had the same high pressure and no go on compressor and Gerald helped us thru that. It is mainly getting the trinary switch to turn on the compressor but there is ways you impede that if you do not do it correctly, and that is what we were doing.

If you need any part info let me know but talk to Gerald as he can get you straight on how to add refrigerant and all other methods to get you going.

We now have very nice dash air.

[Edward Buker]

Dick,

On my 2002 Marquis the condenser fan is wired so it is always on when the button on the air control panel is selected. If that was the case on yours, the condenser fan was wired onto a separate breaker on the ignition switched buss. It is labeled on the door diagram. From there it went through a Hella relay down on the lower right of the electrical bay. From there it went up to a coupling buss above the relays where the chassis wire from the condenser fan was tied in. It was on a stacked couple of nuts and the eyed type crimped connectors. From there on mine heading to the chassis I found a nearly open wire (44ohms) that went to the + lead of the fan. You can check yours by running a temporary wire from that terminal in the bay to the plus side of the condenser fan. See if it comes on with the ignition switch and the air button on. Not sure they are all wired the same but this wiring bypasses any trinary switch for the condenser fan. That is the first wiring issue I have ever had with this coach, the wiring is really top shelf on these coaches.

If your fan does not come on and pressures are that high you could wire your fan on in the same manner as mine and see where your pressures end up.

If the fan is on with pressures that high then  a stuck expansion valve is probably your next item to consider replacing. I am not familiar with the different expansion valves and what is going on but if BCS stocks it they should be able to tell you what is up.

Later Ed

[Doug Allman]

Dick, that is the expansion valve you had in the picture and our old one was stuck or very intermittent so we changed and then had no trouble with system coming into standards to cool. Again Gerald is the guy whom helped us understand what to do.

[Edward Buker]

Dick,

You should be able to check the incoming voltage on the trinary switch and see if the wiring is passing current and voltage to the compressor clutch, within the pressure specs of the new trinary switch. A resistance measurement between the trinary lead to the clutch and the wire that feeds 12v to the clutch should tell you if that piece of the harness is OK. You can use a resistance measurement or a voltage measurement at the clutch under load. Either of those will tell you if the wire is OK.

It would appear to me from my problem that as things fail, like the winding on the clutch or the fan motor, a lot of current momentarily may be pulled such that it may cause a wire to fail like mine did for  the condenser fan. The thermal breakers may not be responsive enough to prevent that under some circumstances.

If you get a length of extra wire and use your meter to measure the legs of the wiring path for resistance you will know if they are OK and how it is wired.

Later Ed

[Dick Simonis]

Thanks for all the input with a little bit of luck we'll solve this problem Thursday.

In summary, this is what I think I know about how the dash AC works:

1)  The trinary switch really functions as a binary switch that senses low pressure in the AC high side and there is no High Pressure cutoff.  When installing a new trinary switch you determine which of the four leads to use the switch after the switch is pressurized and you connect the leads that have continuity.  (that was per BCS when I asked and also the AC tech in Idaho Falls.)  I suspect the trinary switch only controls the compressor clutch and not the fan but not totally sure of that.
2)  There does not seem to be a relay in the compressor clutch and condenser fan circuit.  In addition the condenser fan runs continuously when the compressor clutch is engaged.
3)  There is a circuit breaker for the condenser fan but not the clutch.  That would infer that the clutch could work properly without the fan running.
4)  Power to the clutch and fan is supplied directly from the control head AC on/off push button and presumably in conjunction with the control head temp control (not sure about this).  Does the temp control thermostat actual shut off the compressor or just blend hot air??  I suspect the later is true for the passenger side but may or may not for the master control.
5)  In my case I have power on both sides of the condenser fan CB but no power on the terminal for the compressor.  If I jump power to the compressor clutch terminal both the fan and clutch are engaged.  This also is true if I apply power direct to the compressor lead at the compressor.  I have not measured the current draw for each but it on my to do list.

Regarding the TX valve, this is still a mystery to be unraveled.  I somewhat understand how a single acting TX valve functions by sensing the temperature at the evaporator and throttling the valve as necessary to control the temp.  But the second capillary tube (with the nut and ferrule) implies this is a double acting valve and is unusual in a standard AC system.  I'm wondering if BCS shipped the wrong part.  Fortunately Fred is young(er) and slender so he (unlike me) can probably access the valve and see if the second fitting is indeed used. Doug, where did you second tube connect??

The high pressure I will address seperatly but will double check that I have enough charge to close the trinary switch contact.

Meanwhile I would appreciate you folks reviewing my understanding and correcting any errors.

Appreciate the help.

Dick

[Gerald Farris]

Dick,
The A/C temperature on both sides just uses a blend door to mix air flow to achieve the desired duct air temperature.

The extra line that you are concerned about on the expansion valve connects to the evaporator with a refrigerant O ring seal beside the expansion valve. The only reasonable method that I have found to replace the expansion valve on your coach is through the top of the dash. Just remove the defroster duct outlets and the dash pad that they are mounted in by removing the long screws at both ends of the defroster openings and you will see small access holes that the factory cut and covered. Remove the one above the expansion valve area and you will be able to see where to cut a larger hole to replace the valve without cutting anything underneath. Repair the new hole after replacing the valve and reinstall the dash pad.

Gerald 

[Edward Buker]

Dick,

Given both the clutch and the fan come on together, as you have stated, they must be wired in common. That would imply that the power feed for the fan end is somehow at fault. It would seem very strange to me if there was not a relay worked into this circuit given you have make and break contacts with inductive loads involved. The fan alone pulls 14 to 16 amps for hours on end and the clutch draws about 4 amps which is a total of 20 amps. That switch on the panel I think is meant to energize a relay coil. Some info and schematics here...

http://www.silveradosierra.com/how-to-articles/how-to-repair-gmc-ck-series-trucks-hvac-control-unit-t77522.html

If you trace the wire from the breaker does it travel to a relay in the electrical bay? It just does not seem plausible that this kind of load is direct switched at the control panel push button. Hope this helps.

Later Ed

[Dick Simonis]

Gerald, thanks for the advice on accessing the TX valve that will be very useful if it needs to be replaced.

Ed, I totally agree that a relay should be in the system...somewhere... but it's not in the electrical bay.  I traced the compressor wires from the terminal to two of the multi pin plugs but haven't gone any further.  Fred concurs with that thinking and mentioned that he has seen relays for the AC system tucked away under the dash near the control head but I don't believe he was speaking Beaver specific.  Whatever is the issue I suspect the answer is something quite simple once it's located.

[Edward Buker]

Dick,

Somehow between your coach and my coach in 2002 they changed the wiring and I wonder if it wasn't for a reason. It would not be too hard to have the control head wire feed the coils of a pair of relays added in the electrical bay for current handling. Feed the NO contact through a thermal breaker with 12V from the switched buss and feed the switched output to the condenser fan that will pick up the clutch given they seem to be wired together and work simultaneously. May be easier then going on safari looking for the missing relay. Good luck with this.

later  Ed

[Doug Allman]

Dick, In ours the line with the nut connected to a port and the line with the tube was wrapped around the refrigerant line metal end and covered with insulation.
We did all this by working our way up into the front cap and firewall area, then leaning over the gen set and around other obstacles. We did not follow Geralds advice and remove the dash etc to access the TX valve. We were so close to finishing we just forged on with thin helpers. Is not any fun.
Doing again I will follow Geralds advise. He is as always right on and the best advise on these matters that we have found.

[Dick Simonis]

I just got back in from the barn where I was checking a few things.  First I jumped the clutch to the battery side so I didn't have to turn on the ign and, as before, both the fan and clutch engaged.  This time I took several current readings and this got interesting.

Clutch....~1.7 A
Fan.......~10.6 A
Jumper...~2.0 A

I had to repeat he readings several time to make sure but his certainly suggests that by jumping to the clutch terminal it also puts power to a relay coil for the fan.  This also leads me to believe that the fan circuit is just fine and if we can find out why I'm not getting juice to the clutch circuit all will be well.  I see three points where there could be a problem:  Trinary switch which is new, the on/off button, or a hidden relay.  Right now the relay is falling out of favor since the clutch current is so low virtually any switch could handle it without an issue.  I'm also wondering if there might be a fuse somewhere in the clutch circuit since it would be odd to have a circuit with no over-current protection.

Of course there is always the possibility of a wiring issue.  There seems to be two connectors that the clutch wire goes through; C9 to the firewall and C-51 to the engine bay.  However, the fact that I can make both work just fine with the jumper would seem to rule out a wiring issue in the harnesses.

While I was mucking about the the system I also fired up the engine with the jumper and place and checked the pressures.  With both fans running on high the high side got up to ~350 psig and the low side at ~30 psig.  The high side pressure started a ~200 and than slowly crept up to the 350 mark.  Just for giggles I than moved both fans to low and the high side dropped a bit that went back up when I turned the fan speed back up.  Outside temp was around 90F but still this seemed a bit high.  However I could watch the TX valve operate so it's not just stuck open or close.  I'm wondering if there might be some moisture in the system that is causing ice crystals to form in the valve and partially restricting the flow.  Admittedly I'm outside of my skill set at his point so a bit of guessing is in order.

Tomorrow Fred will be here so we'll see how this plays out.

[Dick Simonis]

UPDATE:  75% resolved yesterday

Yesterday we dug into the electrical issue where the compressor clutch was not engaging.  Dropping the control head was fairly simple but did not yield any useful information.  There is a circuit board and two multipin connectors but without any pin out information doing anything but rudimentary trouble shooting is difficult.  Fred did find one lead that was energized when the AC button was pushed so that as least was positive.

The most fruitful test was attaching two jumpers on the leads for the condenser thermostat and when we would touch them together we could hear a relay clicking.  On the right side of the electrical bay there are 12 relays mounted vertical and simply labeled 1 thru 12 that I had thought were installed as part of  the SMC manual jack conversion.  It turns out that relay #11 is used for the AC compressor clutch and it was bad.  A quick swap of one of the other relays immediately brought the AC back to life.

Of course now I can't help but wonder what other surprises this relay stack has to offer.  Are these relays installed in all coaches of this era??  Does anyone else have these??

As to the higher that normal high side pressure my first inclination is to evacuate the system ans pull a good vacuum for a couple of hours, recharge and see of that helps.  Fred suggested that we pull also check for hose deterioration since he had a similar problem with his coach whereby debris caused a blockage.  Reckon that's my needs to be done as well.

Meanwhile I now have dash AC that is blowing nice and cold so we're moving in the right direction.

[David T. Richelderfer]

Our coach has the same relays just inside the left side of the electrical bay door - 12 of them like in your picture.  The schematic glued on the inside of the door does not show their function.  You have me wondering if one of those relays is responsible for my dash fan/ac/defrost control head problem discussed in another thread which I started.  I will check into that deeper when we get to Yuma in a few days.

[Steve Huber Co-Admin]

Dick,
Here is the diagram showing the relays.
Steve