I have a hissing sound under the dash when running the air conditioner. I checked the high and low pressure with a set of manifold gauges and had to put a can of R134A in to get the compressor clutch to come on.

The ac starts to cool down to ambient outside air when the condenser cooling fan kicks on but starts blowing warm air again when the cooling fan kicks off. the AC Clutch runs constant, it does not shut off at all.

When the condenser cooling fans comes on, the high and low gauges drop down to about 20 low, 150 high. Both High and Low sides are going up in psi and coming down in relation to the condenser or radiator fan coming on.

My guess is the hissing sound is either something wrong in the AC units expansion valve or evaporator under the dash. The hissing sound seems to stop when the cooling fan comes on and starts up when the cooling fan turns off.

Does anyone have any info too share or a steps of how to remove the dash to access the AC unit?

I have a electronic leak detector coming in the mail and have done the UV dye test but haven't seen any leaks.

Thanks for any advice with whats causing the hissing sound.

 

The hissing sound is caused by the system being low on charge. the expansion valve is supposed to meter liquid Freon but when the system is low it is metering gas so you hear the hissing. Discharge lines are known to leak as well as the condenser. I have also seen leaks at the rear extension tubes where they meet the rear expansion valve.

 

Does anyone know what combination of dash buttons allow you to run the ac diagnostic tests and check for DTC codes that don't show up on the OBD scanner? This is a 2008 Dodge Grand Caravan.

Thanks

 

In 2008, the hvac system went to scan tool only diagnostics. Can't even do a system calibration without the scan tool.

 

I have an Actron OBD scan tool I hooked up but there are no codes. I'm pretty sure this isn't the same scan tool your talking about?

Can you give me an idea of the name and what type of scan tool I could try to buy?


Thanks

 

not sure, I'm a dealer technician so not up on my aftermarket stuff. Most OBD stuff is just for engine and trans stuff, they don't do much for the other controllers.