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I have a 88 240 that the blower motor blows out of the front and floor vents at all times. No defrost. I am getting vacuum from the intake through the firewall and to the reservoir at about 16 psi(?) of vacuum. Though the reservoir it begins to build vacuum. How can I get the hvac system to only blow out of the front vents? I’m sure it is a vacuum leak.
also I have tested each bellow individually except I believe the recirculating one. I have the dash off and am not really in a huge rush as it isn’t my daily yet. But it is still frustrating me. Please help!!!
on an 88, the vacuum control of the vents is pretty simple, the push button block directs vacuum to the various bellows, on when button is pressed, off when button is out. best tested with a mityvac [1] that has a gauge and a few adapters and scraps of vacuum hose, so you can T into various lines and see whats going on.
I believe the front vents are always supposed to be on unless you manually close them, the while heater/defrost controls the feet and upper vents. but its been quite awhile since I've dealt with a 240 so I'm a bit foggy on the specifics.
on an 88, the vacuum control of the vents is pretty simple, the push button block directs vacuum to the various bellows, on when button is pressed, off when button is out. best tested with a mityvac [1] that has a gauge and a few adapters and scraps of vacuum hose, so you can T into various lines and see whats going on.
I believe the front vents are always supposed to be on unless you manually close them, the while heater/defrost controls the feet and upper vents. but its been quite awhile since I've dealt with a 240 so I'm a bit foggy on the specifics.
I have been using my mityvac while trying to figure out the problem. I think the reservoir is my problem. I am going to get a cheap $15 reservoir and try that out and if that is the problem I will just mount it in the engine bay and bypass the faulty one... the one in behind the dash won’t hold pressure.
Has as anyone just capped off the vacuum line going into the firewall and used a 12v electric vacuum pump?
hook it up to the mity vac, read the vacuum with the engine idling, shut the engine off, the vacuum should last for several minutes at least.
when working properly, hours after shutting off the engine, you can push the heat and defrost buttons several times and hear the flaps actuate from the residual vacuum in the cannister... after a half dozen cycles, they will slow down, then stop working.
if you have the heater control out of the car, you should be able to hook up the mity vac to the vacuum input, and while pumping it, push one of hte heat/defrost/recirc buttons, and 'feel' the vacuum come out that port, til you push the button again. and if you hook your meter up to the hose that normally goes into that input port, start engine, you should see your manifold vacuum (around -7 to -9 PSI at idle?), and when you shut off the engine, it should hold indefinitely if the cannister isn't leaking.
hook it up to the mity vac, read the vacuum with the engine idling, shut the engine off, the vacuum should last for several minutes at least.
when working properly, hours after shutting off the engine, you can push the heat and defrost buttons several times and hear the flaps actuate from the residual vacuum in the cannister... after a half dozen cycles, they will slow down, then stop working.
if you have the heater control out of the car, you should be able to hook up the mity vac to the vacuum input, and while pumping it, push one of hte heat/defrost/recirc buttons, and 'feel' the vacuum come out that port, til you push the button again. and if you hook your meter up to the hose that normally goes into that input port, start engine, you should see your manifold vacuum (around -7 to -9 PSI at idle?), and when you shut off the engine, it should hold indefinitely if the cannister isn't leaking.
Ok this gives me a good direction of the next steps I need to take. I won’t be able to look at it until tomorrow but I will get back with the results. What is the name of the valve on the intake manifold?
Ok this gives me a good direction of the next steps I need to take. I won’t be able to look at it until tomorrow but I will get back with the results. What is the name of the valve on the intake manifold?
its inline on the vacuum hose, somewhere between the manifold and firewall. I've seen various configurations on 240's, there's a fat vacuum line that goes to the brake booster, that has a larger check valve on it, I've seen a T on the line after that one, with the hvac vacuum line off it...
its inline on the vacuum hose, somewhere between the manifold and firewall. I've seen various configurations on 240's, there's a fat vacuum line that goes to the brake booster, that has a larger check valve on it, I've seen a T on the line after that one, with the hvac vacuum line off it...
Ok so I could take it off and blow through one side of it but shouldn’t be able to blow through the other-correct?
08-26-2019, 09:04 PM
HVAC vacuum nightmare
