I have a 2000 expy and am wanting to know how the HVAC system works? There is a front unit and a rear. I am thinking about replacing the water pump with a electric one. The reason for this is if I have to get out of the truck and I want the heater or AC to stay on, would switching to a electric water pump do the trick? Also is there a reason why the rear unit will not come on by itself, but only when the front unit is on?

Any help in understanding the system would be helpfull, thanks

 

Your Rear heater probabley works like the rear heat in the 2000 Ford Econoline's that our church uses for church buses. Which they work like your home HVAC system does by reversing the AC. Thats why it doesnt work unless you have the front heat on because that tells the system which diretion to run. If so your rear heat will not work unless the engine is running too. With an e-Pump hard wired to a switch or on a thermostat switch your front heater should work untill the engine cools off, which proabably isn't going to be very long. You will also have to wire your blower motor to run with the key off too. No more time than it would probably take for it to cool off you likely used more gas by shutting it off and starting it again than you would have if you would have just let it idle.
-----s the system which diretion to run. If so your rear heat will not work unless the engine is running too. With an e-Pump hard wired to a switch or on a thermostat switch your front heater should work untill the engine cools off, which proabably isn't going to be very long. You will also have to wire your blower motor to run with the key off too. No more time than it would probably take for it to cool off you likely used more gas by shutting it off and starting it again than you would have if you would have just let it idle.
-----s the system which diretion to run. If so your rear heat will not work unless the engine is running too. With an e-Pump hard wired to a switch or on a thermostat switch your front heater should work untill the engine cools off, which proabably isn't going to be very long. You will also have to wire your blower motor to run with the key off too. No more time than it would probably take for it to cool off you likely used more gas by shutting it off and starting it again than you would have if you would have just let it idle.

Ignore the laem which diretion to run. If so your rear heat will not work unless the engine is running too. With an e-Pump hard wired to a switch or on a thermostat switch your front heater should work untill the engine cools off, which proabably isn't going to be very long. You will also have to wire your blower motor to run with the key off too. No more time than it would probably take for it to cool off you likely used more gas by shutting it off and starting it again than you would have if you would have just let it idle.

Ignore the last paragraph, this board has been doing som wierd stuff to my post the last few days and it wont let me delet it out.

 

Unless I'm mistaken, isn't the "rear" HVAC unit in your Expy in the center console?

Does the front control of your expy also have switches for the rear so you have the option of controlling the rear or having rear passengers control it? If so, it's that integration which prevents the rear from coming on all by it's lonesome.

As for your electric water pump to keep the heat going: It would only last approximately 20 minutes before there isn't enough heat in the coolant to keep heating the vehicle. I believe Mercedes has this type of function available.

You could use an engine block heater, but be prepared to kill your battery. A/C without the engine running ( if you had an electric motor driving the compressor and e-fans up front by the condenser) would kill the battery quickly.

 

The rear AC unit is locate over the driver side tire in the back. The controls are in the center console. Idealy what I would like to do is be able to turn the rear AC unit on without the front, so you get the effect just not the direct heat or cold. More to maintain the temp wants it feels comfortable. I dont think I will be going with the epump just get some pulleys. But the efan definitly. Wanting to get one that I can setup as a puller for now and when I get turboed moved it to a pusher .

 

You are talking some major surgery and lots of mods to get that to work. Only thing you can do is spend several hours pouring over wiring diagrams and schematics and once ou have it planned out. Hope that it doesn't mess up your AC completely if you do get it to work. Or set up a seperate A/C system dedicated soley to the rear for heating and cooling. 2 Air conditioner compressors & systems are not only going to add a lot of weight if you can find a place to mount a second compressor and everything. But will also kill yossage"

You are talking some major surgery and lots of mods to get that to work. Only thing you can do is spend several hours pouring over wiring diagrams and schematics and once ou have it planned out. Hope that it doesn't mess up your AC completely if you do get it to work. Or set up a seperate A/C system dedicated soley to the rear for heating and cooling. 2 Air conditioner compressors & systems are not only going to add a lot of weight if you can find a place to mount a second compressor and everything. But will also kill your gas mileage and a lot of Horse power. You will need the turbo just to be close to previous Horse Power. Plus about $1000 in parts to get started and if you don't fabricate the brackets and presure lines yourself then another $500+. Can it be done?...Yes! Is it worth it?...I wouldn't think so but thats soleur gas mileage and a lot of Horse power. You will need the turbo just to be close to previous Horse Power. Plus about $1000 in parts to get started and if you don't fabricate the brackets and presure lines yourself then another $500+. Can it be done?...Yes! Is it worth it?...I wouldn't think so but thats solely up to you.

 

The engine must be running in order for the rear (and the front) A/C systems to operate. Both systems rely on a single compressor. That is why they are both either on or off together.

That scratches the A/C from your plan.

For heating, an electric water pump can continue to circulate coolant with the engine off, however, the heat stored in the coolant and the mass of the engine will be quickly exhausted leaving only ambient temperature coolant to circulate. Won't last very long...

Sort of scrathes the heating idea, also.

Remember, you can still control the temperature of the outlet air even with the A/C operating. The system just warms up the conditioned air.

Steve