2004 Jetta AC blowing cool

I have been trouble shooting my 2004 Jetta AC because it does not blow very cold. Here is the information I have so far.

-Had a bad fan control module and bad large fan so replaced the large fan and the fan control module so both fans working normally
-Clutch engages when the AC switch is on
-Low pressure side 100 PSI when the AC is off
-When the AC switch is turned on pressure drops quickly to around 40 then drifts backs up to 60 where is stabilizes
-When the AC switch is cycled the temperature of air drops consistent with the above statement

Thoughts? Thank you.

60 is a bit high on the low side. Before you do anything, get a set of gauges from harbor freight. they are junk but work on a few jobs worth and is cheep. what is your high, and low when running. you want to see 30~ low and ~120-150 high depending on your cars specs. Not sure about yours, just in general.
Your next step is to go get an acid test. $9.00 or maybe 5 on amazon. report back once you have done both. (im a pro HVAC btw and there is only a few ways you should work on AC, the can at the store with the hose is 100% worthless garbage and wont tell you diddly squat and will 99% chance damage your system if your trying to fix an issue other than topping off and even at that its a nightmare of damage you can do. never overfill the system. this kills the compressor. The ONLY way to add refrigerant on a working system is to gauge the humidity, temperature of the environment (air around you), take readings on the temperature of the lines on the high and the low, do the math for supper cool supper heat to figure out what pressures you need to be at. anything else is amateur and will damage your system over time or instantly. dont let anyone tell you otherwise. You want a system to last or you want to sell the car and get a quick fix?

What is the duct temp get down to? What ambient temp is the car being tested in?

Normally a 30-40 F drop ambient to duct is considered normal, but there are some other variables that come into play, humidity being one of them.

Air flow blockage across the evaporator (neglected cabin filter) can cause poor transfer of heat.

Lots of debris in between the radiator and condenser can cause similar problems.

Standard practice for me on your car would be:

Verify actual duct temp vs. ambient

Verify fan operation (you said they work... but do they ever come on high?)

Verify intake air obstructions (cabin filter... note, on your car this does not apply for recirculate, however you could still have something that got sucked into the HVAC like a plastic back or something).

Verify system charge amount (the only proper way to do this is to evacuate the system, pull a vacuum on it, and recharge it with the proper measured amount from a machine... no cans here)

In some cases, the variable displacement compressors just get weak and no longer can make the necessary high side pressure required to cause a pressure drop at the expansion valve. If the car was driven around with non operational fans, it often will weaken and ruin the compressor.

Expansion valves are not high failure items on these cars, but compressors getting weak from dead fans (which ARE high failure items) is pretty common.

60 on the low side is high, which means the compressor is not working OR the system is overcharged/too much oil. But remember, the compressor cannot work correctly without proper heat transfer on both the high (condenser) side and the low (evaporator) side.

dont be intimidated. its actually fairly easy to calculate supper cool supper heat index, its a variable that changes your high and low pressure target. AC system is built to take those pressures within +5-10%(depending on the system)

things you MUST AVOID
any stop leak or additive or oil added refrigerant cans what so ever. only r134a PERIOD, no "synthetic" nothing other than pure r134a
any quick fix cans or the ones with the gauge on them
overfilling the system, its ok to be under


Things your looking for to find the issue. get soapy water and spray down EVERY CONNECTION, the lines, and all components and what not. chances are its the schrader valve, or an o'ring.

you can easily top off the system the right way and i do this on 2 of my cars every year but i do it right. with a good set of gauges that are calibrated correctly. I can guide you through this.

btw the acid test is a strip in side a tube you press against either high or low side and let a tiny bit of refrigerant and oil pass by it and into the atmosphere. If it fails the test (turns the brown colour) then your compressor is dying. the metal produced by a compressor dying reacts with the PAG oil and is designed to create a mild acidity in the oil so techs can check the health.

get back to me when you do the test and have your gauges. Yes harbor freight gauges are junk but they will do the job for you a few times. there less than $80 vs the 300 for a decent set that lasts a life time.

Thank you for the replies I will get the gauges to measure high side pressure. A few items I have left out.

-Just changed the cabin air filter and there is good air flow from the system
-The fans do come on high but I am not sure how long the big fan was out I assume a few months due to the slow degradation of the ac temp
-I have not measured air temp but it is definitely not 30 degrees drop
-I have not checked the evap to see if it is clogged, fouled, or somehow not allowing proper heat transfer