1977 Miller Meteor Lifeliner - Rear Air Con/Heater

I have a question. I had the front chassis AC recharged and repaired and is working great. I have never touched the rear unit or even turned it on....

Today I turned the overhead master switch on (AC) (Center Off, up for heat, down for AC) and the rear fans blew when turned on...

Any ideas , thoughts ...how this works..?

I am guessing I need to have the engine running, turn the ac on in the front and try the AC ?

Can I damage anything ?

There is a rotary switch for the fan speed and there is a rocker switch on the panel with the 3 very small gauge wires, I am guessing for the heat thermostat?

I will take some pictures and post tomorrow...I am pursuing this since the rear windows don't roll down and there is only an exhaust vent fan in the rear door...just in case someone rode back there and needed some air, other than the sliding partition window...not a whole lot...

Any other 1977 MM owners have any experiences with this?
 
The rear air conditioning requires that the front air conditioning be running on most cars. There might have been a switch for just the rear air conditioning that you would use to start the compressor on the engine. This would require that the engine be running also. On most of the rear air conditioned cars, they used an aftermarket evaporator and diffuser to cool the rear. The rear air conditioner is an component part of the front air conditioner. When they charged the front air conditioning, the Freon also was going to the rear air conditioning. In theory, they should have had that unit activated at the same time to determine overall performance of the entire unit.
 
Thanks Paul, my local mechanic about 1 1/2 ago actually tool the car to the local Cadillac dealership in northern California who repaired the system. My guess is that they never touched any of the rear air controls.

So I can assume that the "unk" switch probably activates the AC compressor when the engine is running, in case the front AC is not turned on ?

So Paul if the repairs were completed without touch the rear air, would they still have had to use the same amount of refrigerant/freon? looks like they converted the system from R-12 to R132

By turning on the rear air unit, engine running, I really can't un-do any of the repair work that was done for the front system?

mark
 
Thanks Paul, my local mechanic about 1 1/2 ago actually tool the car to the local Cadillac dealership in northern California who repaired the system. My guess is that they never touched any of the rear air controls.

So I can assume that the "unk" switch probably activates the AC compressor when the engine is running, in case the front AC is not turned on ?

Don't know what the "unk" switch does, but whatever it does, will not do any harm if you turn it on. When you turn it on, have the doors closed, so if it illuminates a light in the rear, you will know immediately. With the switch in the ON position, and the engine stopped, and the front air conditioning lever set to off, start the engine with the hood opened, and see if the compressor is turning. If it turns, then go to the rear, and turn the switch off, and if the compressor stops, then you will know for certain that is what activates the rear air conditioning when the car is running, and the front air conditioning is in the off position.

So Paul if the repairs were completed without touch the rear air, would they still have had to use the same amount of refrigerant/freon? looks like they converted the system from R-12 to R132

In theory yes. When converting from R12 to R134, the formula is to use 80% of the specified quantity of R12. Assuming that your car originally called for 5 pounds of R12 refrigerant, then the correct amount of R134 refrigerant would be 4 pounds. Some shops don't use a refrigerant scale
to install the refrigerant, and keep installing refrigerant until they see the refrigerant running clear in the sight glass at the top of the receiver drier.

Converting a system from R12 to R134 requires changing the type of oil in the compressor, flushing the system of the old oil, and replacing the some additional components. To what extent the dealership did all these things is difficult to know, unless they itemized them on the invoice. This is why I personally don't like switching refrigerant from R12 to R134. The time (dollar cost) to do this correctly vs. the higher cost of using the more costly R12 works out to being equal usually. The R134 molecule is smaller than the R12 molecule, and the old rubber hoses that were able to contain the R12 molecule, can't contain the R134 molecule as well. When the automakers switched to R134, the hoses also changed from a reinforced rubber hose to what is known as "barrier" hose. This hose has an internal material that can contain the R134 molecule. On my 1962 Chevrolet, I had to replace all the rubber hoses, since they were hard and no longer able to contain the refrigerant without its leaking out in a few days. Since the original rubber hoses were no longer available, I used the new barrier hose. I also refilled the system with R12, since that is the refrigerant that it was originally designed for.

By turning on the rear air unit, engine running, I really can't un-do any of the repair work that was done for the front system?

There is nothing that you can do damage to the system by turning on the rear air conditioning switch that will un-do any of the previous repair work. If you find that the rear air conditioning doesn't work, and the front air conditioning is working properly, then the fault lies in the rear air conditioning unit. Most likely, it is a defective expansion valve, which will require the entire system be evacuated to replace the expansion valve. If this is the case, it will be up to you to determine if its replacement is cost effective.


mark

.....................
 
Well I checked and it blows cold air...all seems to be working so far....

Thanks again Paul
 

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The white switch is master. It powers the panel. The should be a AC heater switch. Then the power vent. All the AC/heater switch does is change which blower comes on. Hot water has a cable pull that shuts water flow on or off. The front ac has to.be on for the compressor to work. But as you did not own the car new who can say who did what over the years. Properly charged the air out of the unit should be 34-36 on 134.
 
FYI The switches do the following,

Left to right

Unknown Illuminated White Rocker

Black Rocker - Rear Door Exhaust Fan

Patient overhead light (dimmer)

Patient Compartment side lights (dimmer)

3 Speed Fan blower for HVAC System

Three black Illuminated Rockers (Red/Yellow/Green) patient Status lights
 
No rear heater? Then there should be one that was momentary for the door locks that never work.but only if they were front opening doors.
 
OK, I am headed over to the shop and I will take a few more pictures...since that switch does not match any that MM installed, I suspect in may have been a control switch for a power inverter that was mounted under the patient floor ...I think I recall seeing the wires down there....more details to come

Thanks so far for all the input..... Brady Smith or Warren Waterman, have you guys had any experience this ?
 
Here are some pictures of whats behind the seat...I am trying to find out where the air in-take is ...Where does the fresh air enter the system, from under the car ????

Still have not found out where the mystery switch conencts, not under the patient floor like I thought.....
 

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I take it this one is mounted in the divider. Air would enter from the cab. The heater should be left rear. That is if it has one.
 
Mark,
I just finished repairing the a/c in my 77 Lifeliner last year. Previous to that I was not getting anything for airflow in the patient compartment. Now it blows nice cool air back there. I replaced every component I could find in the system, including the auxiliary filter dryer for the rear ac unit.
My heat does not work, both in the cab and in the patient compartment, but my hunch is that I have an airlock in my heater core and a coolant flush will solve that. But I digress.
It drives me crazy that the second row doors don't have roll down windows. I hate the idea of having to rely on a 40 year old system to keep passengers cool back there.
Let me know if there is anything else I can help you with.
Kurt
 
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