Why is there constant vacuum to heater control valve ?

[Burnsy]

2001 ranger 3.0 flex fuel...when truck is running theres constant vacuum to the heater valve......when I shut off the motor the valve doesn't release, the little lever on the valve stays engaged/sucked in, still under vac.....if I pull the vac line off the valve nipple the vacuum releases, otherwise its always under vac,......most people post with no vacuum, i have the opposite problem , thanks for your replies

 

[Dirtman]

Is your AC on...

 

[Burnsy]

Is your AC on...

Theres vacuum when in ac max and when system ac is off.....therws NO vac when in just reg ac mode .....maybe that's normal ?

 

[Burnsy]

Theres vacuum when in ac max and when system ac is off.....therws NO vac when in just reg ac mode .....maybe that's normal ?

Also no vac when in fan mode and heat dial turned to hottiah

 

[Burnsy]

Also no vac when in fan mode and heat dial turned to hottiah

Meant to say hottish

 

[Dirtman]

Yea that's normal operation. When vacuum is applied the valve is bypassing the heater core. In max AC the heater core is bypassed to make the AC more effective.

 

[Burnsy]

Yea that's normal operation. When vacuum is applied the valve is bypassing the heater core. In max AC the heater core is bypassed to make the AC more effective.

Thank you......also, when ac is in "off" there is vacuum......normal ? And when I shut off motor the valve stays closed/vacuumed/bypass core is that normal also ? Thanks

 

[DILLARD000]

If you got the HeaterControlValve pictured below, it operates Vac=Close\NoVac=Open.
I've replaced that junk plastic BallValve that tends to crack+leak,
with an old style metal PlugValve, which also operates Vac=Close.

 

[Burnsy]

If you got the HeaterControlValve pictured below, it operates Vac=Close\NoVac=Open.
I've replaced that junk plastic BallValve that tends to crack+leak,
with an old style metal PlugValve, which also operates Vac=Close.
View attachment 63682View attachment 63683

Thanks yeah I have that one, turns out it waS operating normal vacuum wise but I noticed it leaking a little so I replaced it

 

[RonD]

Heater by-pass valve should only have vacuum when MAX AC or OFF is selected, no vacuum in any other setting

Standard Ford HVAC vent control seen here: https://www.ford-trucks.com/forums/attachment.php?attachmentid=517&stc=1

On the right you will see the White vacuum hose, it controls inside fresh air vent AND goes thru firewall as a Grey vacuum hose that connects to the Heater by-pass
It should only have vacuum in MAX AC and OFF as seen in diagram

The whole system gets vacuum from the vacuum reservoir(tank), black hose at the top, so even with engine off there will be vacuum present from the reservoir

Temp control is Electric, the Blend Door actuator, it sends air from the fan thru the heater core or around the heater core or anywhere in between

 

[Burnsy]

Heater by-pass valve should only have vacuum when MAX AC or OFF is selected, no vacuum in any other setting

Standard Ford HVAC vent control seen here: https://www.ford-trucks.com/forums/attachment.php?attachmentid=517&stc=1

On the right you will see the White vacuum hose, it controls inside fresh air vent AND goes thru firewall as a Grey vacuum hose that connects to the Heater by-pass
It should only have vacuum in MAX AC and OFF as seen in diagram

The whole system gets vacuum from the vacuum reservoir(tank), black hose at the top, so even with engine off there will be vacuum present from the reservoir

Temp control is Electric, the Blend Door actuator, it sends air from the fan thru the heater core or around the heater core or anywhere in between

Thanks !

 

[Burnsy]

Thanks !

Heater by-pass valve should only have vacuum when MAX AC or OFF is selected, no vacuum in any other setting

Standard Ford HVAC vent control seen here: https://www.ford-trucks.com/forums/attachment.php?attachmentid=517&stc=1

On the right you will see the White vacuum hose, it controls inside fresh air vent AND goes thru firewall as a Grey vacuum hose that connects to the Heater by-pass
It should only have vacuum in MAX AC and OFF as seen in diagram

The whole system gets vacuum from the vacuum reservoir(tank), black hose at the top, so even with engine off there will be vacuum present from the reservoir

Temp control is Electric, the Blend Door actuator, it sends air from the fan thru the heater core or around the heater core or anywhere in between

So you're saying with he engine off the system will remain under vac ? I thought I remembered the vac relaxing with the motor off and then the little arm on the valve getting sucked in when the motor starts.....i say this thinking back to my other old ranger.......and recently I changed out my blower motor resistor(fixed the fan speed issue) and after that the vac relaxed when motor shut off. I was like hey I got my vac working properly by changing the reaistor somehow......a week later(yesterday) I noticed it doing the old thing, staying vac'ed when the motor is shut off........is my memory or logic flawed ?? Before I shut off my engine i always turn off the ac....I don't think this would affect things.....my issue is with motor shutdown/retaining vac........and when in ac max I set dial to coldest setting and lowest air speed usually, I don't think that has anything to so with it but just including that info in case...thanks for any input sorry for any redundancy just trying to get it straight in my head

 

[fastpakr]

My 99 had been torn down for the last few weeks. Yesterday I inadvertently knocked the vacuum line to that valve loose while reconnecting things. There was an immediate hiss as the valve moved. It had clearly been under vacuum the entire time.

 

[DILLARD000]

It's VacToClose, so that if vac fails, it defaults to being open; a safety feature to provide engine cooling & cab heat.

 

[RonD]

Vacuum systems don't technically "use up" vacuum(negative) pressure when "on"

i.e. your power brake booster, you turn off the engine, vacuum source, come back a month later to start engine and brake pedal still has assist before starting engine, why?
Because the negative pressure in the booster is still there, its only used when you press pedal down, and its just "used" to assist you pressing down the pedal, so doesn't dissipate over time unless there is a leak

Same for the cab vent system, if there are no leaks then reservoir to cab vent motors will hold vacuum for months and months
Its negative pressure, so the connections tend to pull together limiting leak points

Any valve can stick open or closed, that's just the way mechanical systems are, ever try to turn off a water valve under a sink that has been on for 10+ years, lol, sometimes its stuck
So yes, by-pass valve could stick closed, or open, but its not because its a vacuum valve, it's because its a mechanical device

Previous Owners.................always a unknown on used vehicles, lol
People see a vacuum hose in the engine bay and its disconnected, they re-connect it to vacuum source, the engine
So previous owner may have connected Grey line to a full time vacuum source, by mistake