Why does my Volvo 740 make a hissing sound?
Leaking Sound from Heater Controls. [John Sargent] One of my 740s made a hissing sound from under the dash in the area of the heater temperature control lever. The manual heater control assembly supplies vacuum to the under hood heater valve to shut off coolant flow to the heater core in the cold position of the control lever.
What are the symptoms of a Volvo B6304 engine?
Symptoms for B6304 engines used in the Volvo 960/90 series cars with Bosch Motronic are covered in a separate 960 file. Diesel symptoms are covered in the diesel file. Some notes relate to carburetted cars: they are identified as such. General Symptoms and B2XX Series Engines: Don’t Panic: Diagnose First Before Concluding the Worst! Idle Problems:
What kind of problems does the Volvo 960 have?
[Editor: 960/90 series cars suffer from numerous wiring and electrical troubles, all explained in the 960 section Emission Control Problems (High HC, CO, NOx): Emission Control Problems: High HC, CO or NOx Abbreviations: AMM = Air Mass Meter ECT = Engine Coolant Temperature sensor
Where is the vacuum valve on a 1990 Volvo?
Vacuum Check Valve Failures. [Inquiry] I have a 1990 760T and the H/AC is losing vacuum during low vacuum and during boost from the turbo. There is a tee above the intake that has two black & white fitting that connect to two smaller hoses that go to the fire wall.
When do you close the water valve on a Volvo?
[Response] Vacuum to close the water valve is only applied in max AC mode or when the MCC temperature selector is fully cold. This varies according to the type of control system in the car (MCC, ACC, ECC) and the Volvo OEM service manual should be consulted for details of vacuum signals.
Why does my Volvo air conditioner not shut off?
Heater Won’t Completely Shut Off Hot Air. [Tip from John Sargent] 700 series, with manual temperature selection, have a reputation for not being able to completely shut off all of the warm air when the manual temperature selector is fully off. The problem is the flapper door in the heater is not fully closed.
What to do if your air conditioner is hissing?
Connecting the vacuum hose to the heater valve cured the hissing sound, and shut off the flow of coolant through the heater core. See also the notes below under Vacuum Check Valves. See instructionsfor help on removing the vacuum hoses at the back.
Where is the vacuum hose on a Volvo?
Leaking Sound from Under Dash. That vacuum leak is almost certainly your floor/defrost diaphragm. It is on the left side of case just above the accelerator pedal. This diaphragm unit is double acting, i.e. it has vacuum to pull it both ways, blue hose for defrost and yellow for floor.
Why is my air conditioner not working in my Volvo?
You have a vacuum leak which causes the heat vent control to work improperly; Your firewall-side heater water valve was installed backwards; The arrow on the valve points to towards the firewall inlet, not back towards the engine. Control cables from the heater control unit to air mixing doors are maladjusted or broken.
Where is the flapper valve on a Volvo air conditioner?
The problem is the flapper door in the heater is not fully closed. There is an adjustment for this in the cable, just behind the heater control. If you remove the glove compartment, you can see the heater controls. The cable on the bottom controls the flapper valve for heat. The adjustable part of the cable is at the heater control.