Patient Compartment Heating/AC Troubleshooting Help

Kurt Halverson

PCS Northland Chapter President
Hello Everyone,
I am working on my 1977 Lifeliner, and I am trying to figure out the heating and ac system for the patient compartment. Since I have had the car, I have not had the system working.
Is there any special tricks to getting the system to work? For example, does the car's own heating or ac system need to be running for the auxiliary one to work?
Also, I know inside of the rear loading door jamb, there are a few different switches that are triggered by the door being shut. I know one is to set of the warning light in the cab for "door ajar", and another is to turn on dome lights. Is one of these switches in line with the heating.ac system where it won't run unless the rear door is shut?
The other night I took down the housing that holds switches that control the patient compartment dome light and there is another switch that says "heating/air conditioning". This switch seems to have multiple settings, so I think it is for fan speed. Running from this switch were two wires with round devices in line. What are these? They look like they may have gotten overheated, and that could be part of my problem.
IMG_20140615_210021_272.jpg


Thank you in advance for your help!
Kurt
 
Not familiar with the Miller Meteor system for 1977, but I can answer the question about the two yellow parts, and what I know about thse systems in general. Those are wire splices with heat shrink tubing, but they look like there was some form of resistor installed in the middle. At this point, you have nothing to loose, by cutting the yellow plastic away, and examining it further. Also, the air conditioning must be working up front for the rear air conditioning to be working, unless there is a bypass to activate the air conditioning compressor from the patient compartment. The heater would have hot water flowing through it, if the heater hose take off tee is located forward of the Cadillac vacuum controlled heater hot water valve. If the tee is located after the Cadillac vacuum controlled valve, then the drivers compartment heat control has to be in the heat mode. It is possible to hook this up either way, depending on what the body builder had in mind when the vehicle was purchased.
I would make sure that the drivers compartment heat and air conditioning system is functioning as designed before I try to trouble shoot the patient compartment unit.
 
heat is hot water from the engine. the AC will only provide cooling if the compressor is running. one question does your's have a house type thermostat on the bulkhead? I thinking not from your description.
the connectors your showing are not in good shape they have gotten hot enough to most likely not be making connection. so that repair is in order.

normal operation is master panel on with car running. front controls set for the correct position for desired climate control.the heat cool switch should click the switch in the unit to which ever you have selected. there will be a separate switch for the fan speed in back for the rear unit. that is if it's a one piece unit. yours most likely is . older cars had a ac unit and a heater. most had a water shut off either cable controlled or a screw valve under the hood to shut the water off when heat was not needed.

but I would first check if you have power to that set of splices. I'm guessing heat one wire and cool the other. if that switch provides power to those wires them the seat controls are good. but to do the power check start at a good source and work your way to the end. believe it or not those connection look typical for the rear system. not good but you see it a lot. if you trace those wires to the unit it may be fan control. with one wire power with the heat and one power with cool. both just running the fan.
 
Not to hijack the thread but it is related to topic. Is there a second heater coil for the rear heaters on ambulances?
 
most have the heater out let at the foot well and ac unit in the rear. completely separate units. but the newer one may be the combination unit like you find in a limo rear unit. I'm only guessing from the pictures
 
Open Circuit?

The inline devices shown in your photo may be diodes- or one way "gates" or check valves for current. They do appear to have been overloaded, and if they blew, one or both circuits may be "open" or incomplete. You can test by using a continuity meter. If they are diodes, and are functioning, you will have continuity one way, but not the other. If they are damaged, you will lack continuity in both directions. Diodes are rated in amps.
 
Why would the current be flowing in more than one direction in this application? The only place that I know of diodes being used in that era car is in the alternator. Possibly a resistor is under the shrink wrap, but I can't see any reason that they would be putting a diode in the line.
 
either way it's a trace them out. were do they come from and were are they going to? mounted on the plate is strange and so is using zip ties to do it, but I'm still wondering if the car has the thermostat control or switches only? picture of the controls would help as would pictures of the unit in question. I have not had the pleasure of getting to play in in one of the newer ambulances.
 
Hi Gang,
So I opened up the shrink wrap on the parts in question, and I found out by looking up the part number that they are Motorola blocking bypass diodes. I am not sure why Miller Meteor used them in the circuts, but they must have had some reasoning behind it. There are two of the diodes coming of the fan speed switch, which is shown in the picture below as "rear heat air condition" This switch has multiple settings, so I think it controls the blower motor for the patient compartment.
IMG_20140619_213518_436.jpg

The diodes measured about .664 ohms of resistance. I am not sure what a good one measures, but I found them for sale on Ebay, and I have a few on their way to my home to check out.
Ed was suspecting that I have a thermostat in the patient compartment, and he is right. Here is a picture of it:
IMG_20140619_202601_540.jpg


Thanks again everyone for your thoughts and advice. I will check out the new diodes to see if they have a lower resistance, I assume they should not have any. Hopefully that will be all it takes, but if not, I will follow the advice of tracing wires.

Kurt
 
there will be no resistance with the diode. it only controls the direction that current can flow. I would guess its used to prevent feed back to the thermostat and blower switch. I'm told the thermostat just controls the blower. heat or cool is most likely set from the front controls. the bench switch would set the blower speed the thermostat would turn it on and off.

if both the wires go to the blower then jump one with 12 volts to see if the blower will run. my bet is it's locked up and that caused the line resistance to heat up the weak link,

with a test light the other side should have power. one when the thermostat makes contact the other will be brighter with each click of the attendants switch.

the two wires to the blower make no since to me. I would have thought that the the thermostat would power the switch, the switch the blower. but they sometimes do strange stuff. it still trace things out before just swamping out the dioeds. find out why they got hot and start your repair there.
 
My best guess is that those diodes were not installed by Miller Meteor, but rather, they were installed by the Motorola dealer that installed the radios. The reason for the diodes, I suspect, is to keep the fan motors from causing interference with the two way radio communication equipment. Unless you are going to have 2 way radios in the car, then they are not necessary. I would just replace them with a fuse or nothing, since the circuit is already protected elsewhere.
 
it does seem strange with a typical MM splice with in a couple of inches of it and the chip board hanging in free space. MM was decent about tying things down. if both the wires power the blower motor my guess is that the attendants switch would be used to power the blower whether the thermostat was open or closed. the thermostat would close the blower will come on high till it opens again then the blower would drop to what ever the attended seat was set for. heat or cool would depend on what the dash unit was doing?
still bet they have something to shut off the water flow in the system. the Add on rear unit in the 6 doors use a Solenoid that trips a vacuum valve to open or close the water flow. in the 92 Same body as yours the vacuum line is spliced into the heater control vacuum under the hood. that way if the car has the water shut off the rear can not run heat.

but remember that blower on high will run at least 25 amps. it is a major current draw. the fuse for it should be on the MM fuse panel were ever they located it.
 
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