Rear Ambulance A/C

[Chris Elzie]

My ambulance has 2 switches for the ac, one turns on the fans and the other Im not sure beacuse nothing happens. Its a 76 S&S Professional. Does anyone have a basic layout on how the rear ac works? Is there a compressor of some sort in the unit?

[John ED Renstrom]

The front ac has to be on. The unit is just anothef evaporater. So if the ac in the car works and the fan comes on you should have ac in the rear unless someone removed the lines.

[David Henry]

So speaking of S&S A/C the compressor doesn’t kick on unless you jump it in my 74. Is there a relay or something that might not be working. It does have that dial thermostat in the front...

[John ED Renstrom]

Try recharging it.the low pressure switch will not let the compressor come on when you jump it ther is enough pressure t o keep it closed.

[David Henry]

Ok did a leak detection and none noted. The system was charged as doing the change from R12 to current standard juice.

[Paul Steinberg]

Originally Posted by Chris Elzie

My ambulance has 2 switches for the ac, one turns on the fans and the other Im not sure beacuse nothing happens. Its a 76 S&S Professional. Does anyone have a basic layout on how the rear ac works? Is there a compressor of some sort in the unit?

If there are 2 switches in the rear, the most likely situation is that one is for the fan, and the other turns the compressor on, if it hasn't already been in A/C mode in the drivers compartment. Usually the fan is a rotary switch with more than one speed.
If your compressor isn't starting, then check to see if it has the thermal overload protection device somewhere in the electrical line. If this is bad, then the system will not start. I suggest that you check your factory service manual for location and testing procedure.

[Paul Steinberg]

Originally Posted by David Henry

Ok did a leak detection and none noted. The system was charged as doing the change from R12 to current standard juice.

How was the leak detection done? If they used an electrical probe, it doesn't always locate the leak. Best method is to install a can or two of Freon with black light dye or yellow dye. Your car has a very large system, and a leak can be anywhere in the system, including the rear evaporator which is difficult to do a leak detection on. On large systems, I pull a vacuum for a couple of hours, and then add a two cans of Freon with dye, and then pressurize the system with nitrogen, to push the dye to all points of the system. Sometimes even that doesn't work, and you have to start breaking the system apart and install all new seals, and assume that is the problem. If that doesn't cure the problem, then you have to put the full charge of nitrogen into the system, and using a special soap mixture, start spraying the hoses, and hope that you will find the leak. It is time consuming, and you use up quite a bit of expensive supplies before you can find the leak.

[Chris Elzie]

The ac in the front compartment works fine, Im just not getting any cooling in the back. I was thinking the line might be stopped up somehere, because all the hoses are hooked up.

[John ED Renstrom]

The valve in the rear evaporator may be bad.the 134a is what you charged it with? Most of them of have seen were a cobble of factory hoses hooked togeather. One may want to change them to new hose. They could be broken down inside.

[Paul Steinberg]

Originally Posted by Chris Elzie

The ac in the front compartment works fine, Im just not getting any cooling in the back. I was thinking the line might be stopped up somehere, because all the hoses are hooked up.

If the hoses were "stopped up", whatever was in the hoses, would have killed the front air conditioning system. Most likely, the expansion valve has failed. It can't be fixed without draining the system of Freon, and tearing into it. I suggest that you have a professional air conditioning service person take a look at the system.