My girlfriend Anne stopped by on her way through back to Kansas for a few days (which was lovely!), but she was complaining that her A/C was not blowing cold.

Her car is a 2001 Mercury Mountaineer with the good old 5.0 V8 and AWD. It's got more than 130k miles on it. Since I had already thrown $200 into it getting it's differentials cleaned and lubed (The front fluid was scary black!) and oil change, I decided to do this job myself. (It also has an exhaust rattle and badly needs timing or valve adjustment....but it'll have to run bad for a while.)

I used this video from ChrisFix to boost up my knowledge and confidence for doing this particular job.



Step one: Pop the hood.
Step two: Bash the stuck hood a couple of times.
Step three: Pull on release handle until you swear you're going to break it but then the hood gives up and pops.
Step Four: Be pleasantly surprised the hood struts still hold the hood up!
Step Five: Start the engine and run the A/C at its coldest setting with the fan on high.
Step six: Watch the A/C clutch work rapidly on and off. Hmm. That's not normal.
Step Seven: Search engine compartment for low side nozzle. For this vehicle, it was on the passenger side near the firewall. Vigorously shake bottle of refrigerant.
Step Eight: Connect recharge bottle to nozzle and make sure it's clipped on securely.
Step nine: Adjust pressure gauge to outside temperature. Check to see pressure of system before adding any. In my case it was at the bottom of the gauge and then climbed when the compressor engaged.
Step ten: Twist bottle as you pull the trigger filling the system with refrigerant. Use short shots and frequently check the pressure gauge to keep it within the appropriate range.
Step eleven: Marvel at the truck being totally empty of refrigerant and pretty much empty the whole bottle into the system. The compressor also calmed down on the engagement clutch while filling the system.
Step Twelve: Unhook the bottle. Replace the nozzle cap. Close the hood.
Step thirteen: Receive hugs and kisses from appreciative girlfriend. Air went from sweaty sticky-neck hot to sip your ice tea with a refreshing ahhhhh cold. My job is done here!

Anne happily drove herself and her Uhaul trailer to Kansas in a well lubed and chilled vehicle.

 

But was it cold enough to kick Annes high beams on? If not, you should have added a little more! THAT'S when you know it's cold enough! LOL

 

Dude, we have ladies actively on the forum.
Already had to contact Mr Dave to change what was in his post to be less graphic.

Please remain as respectful as you tend to be, except when on the phone w me.....

 

The repair work was appreciated.

 

Typically when the compressor short cycles, it is a dead give away for low charge. EXCEPT if you have a mechanical fan. Then if you are idling, the mechanical fan can't provide a sufficient temperature drop across the condenser coil to keep the high pressure switch from cycling the compressor.

 

If that were the case, wouldn't it show over-pressure once I began spraying in refrigerant? There would be positive pressure at start-up/idle if there was still refrigerant in the system, right? So even though the system is short-cycling, it still shows pressure. In that case, I wouldn't have sprayed in seeing pressure in the system.

 

Yes, if there is any refrigerant in the system you will have some sort of positive pressure. I was just stating that short cycling of the compressor is almost always due to low charge, but in some cases, due to not enough ambient air passing over the condenser coil.

You performed the diagnosis correctly and got your ac working as a reward. Congrats!

 

Close.....

If the system still has any charge in it, you know with all things NOT running, you should read a non-zero static pressure hi and low side---that's how you know the charge is LOW but not not zero (empty).

When the static pressure is borderline low, the compressor will kick in, creating the pressure differential betw high and low side. The low side drops some, and when the lo side pressure drops below the system's design point for low pressure operation, the low pressure limit switch trips, disconnecting the compressor clutch.
The pressures return to near their static values, the low side reaches a pressure above the design cutoff pressure, the low pressure switch will return to its normal position, the AC clutch will re-engage, and the compressor will kick on.

And the whole cycle will repeat until either the system is recharged or more refrigerant leaks out such that the static pressure is below the low pressure limit switch -- at which point the compressor clutch will be inhibited by the low pressure switch being constantly activated.

It will indeed show SOME initial pressure at the beginning (if the system is not empty)--you just take that into account when filling the system. Hence why you should use at minimum a low side gauge to ensure you are not overcharging the system.

This is a perfect example of when using at least a low side gauge can help you figure out the state of your system before, during, and after charging the system

 

DTruck types faster... ')

 

He probably doesn't type faster, derf. He just types a LOT less! LMAO