I took my van to the shop beacuse it would not blow out heat and they replaced the actuator system in the front but now the back wont blow and it did befor and they said they didnt mess with it any ideas?

https://www.manualowl.com/am/Oldsmobile/1995-Silhouette/Download/972
(page #3-4 to 3-6)

plugged front heater core maybe , your vehicle has two heater cores , one front an one back . Or the temp. blend door actuator is bad .

Can you post the model and the year please

No ,there is not another valve . One low side service port an one high side service port . An only one A/C compressor . Under the hood in the engine compartment there are A/C lines going into the firewall . These go to the front Evaparator unit . With the vehicle running an A/C on do this line's (pipes) get cold ? If yes , your problem is probably the temp. actuator . Control's how hot or cold the air coming from the vent's get . If stuck half way , hot an cold air combine to make warm air . Replacing some of these actuators can require the dash to be removed . Your best bet ,take it to a qualified repair shop .

Your most likely problem is a bad head gasket.If you used the bleeders to remove the air from the vehicle and your are sure you got all the air out and you still have no heat and the coolant keeps coming out the over flow bottle.Then the head gasket is bad.Usually the rear head head.But I have also had the front head go bad.The best is to replace both gaskets.You should also have the heads checked to make sure they are not warped if the engine ran hot.Hope this helps.Good luck.Let me know if you have anymore questions.

If you have heat in the front the engine cooling system is operating normally (waterpump ok) If the rear hoses were rusted out you would have front issues too due to collant loss. I sounds like either the rear controller has a problem with the temperature door actuator or an electrical problem going to the actuator. They sometimes have a heater valve which shuts off coolant flow to the rear heater core. It is located in the engine, where the rear hoses split to the rear. They are usually vacuum operated, possibly the valve or vacuum issue, check there. Feel the rear hoses under the van with the rear heat on. One should be hot and the other warm (this would indicate the heater core and valve are functioning). If the rear fan works the fuse is ok for the controller.

The blend door actuator is the most likely cause. It is on the front of the heater box under the dash and looks like the picture below and #14 on the system exploded diagram. Remove the actuator, plug it back into it's cable, turn the key on and change the temperature setting to see if the actutor turns. If not, replace the actuator.

First the switch this may not be bad switch it sounds like a bad blower resistor, this is what controls the speeds, the loss of heat may be low coolant level or a bad blend door actuator, depending on the heat/ac system in the van it may also be a bad vacuum leak in the engine compartment, some models use actuators to control system and some use vacuum, if the system looses vacuum the door will close until vacuum is restored, hope this helps.

where is the heat blend door located 97 ford e-350 van

I think you are on top of your problem,,you dont need any one elses advice.
Complete rebuild of the cooling and heating system,, simple.