Model: Town Car
Engine Size: 4.6L
Refrigerant Type: R134
Ambient Temp: 90
Pressure Low: 35
Pressure High: 200
Country of Origin: United States
OK first time poster here looking for some help, lots of great info on the forums! I just bought a 2003 Town car a few weeks ago and it wasn't cooling properly so I pulled a vacuum down and charged it and it gets ice cold around town at speeds below 60MPH. However above 60 MPH the compressor cycles of and it stays warm in the car. I decided to put a new accumulator because it looked like there was a lot of moisture in the system when I pulled the vacuum, at the same time I replaced the orfice tube and the low pressure switch. I still had the same problem after wards and after a couple weeks it stopped cooling all together. I searched around with the leak detector and found a leak at the evaporator. I was also getting a sporadic reading on the high side(needle bouncing around) and someone said that the compressor was on its way out so I ordered the new evap and compressor and replaced both. Pulled a vacuum down for 45 minutes and held for 15min and it was good so I recharged again to the 32oz on the engine compartment sticker and still had the same exact problem with no cooling on the interstate and the high side needle still bouncing. I put a large fan in front of it in the driveway and give it gas in the to about 2000rpm and the low side drops down to 20 and the compressor kicks off. This happens constantly in cycles of about 5-8 seconds. So I have replaced the evaporator, compressor, accumulator, low pressure switch, and orfice tube to no avail. I have tried a little more charge and a little less, engine sticker says 32oz, service manual(alldata) says 38oz. Neither way helped. Any ideas on what else could be causing the problem?
All indications point to a likely undercharge. Have you weighed the charge in with a scale? If you're using a recovery machine, they can be off. A scale is a good "sanity check" if there is doubt.
If the compressor was indeed going out, the condenser should've been replaced. The condenser could be restricted towards the outlet. Have you run an IR thermometer slowly along the condenser to check for any sudden cool spots, or excessive overall temperature drop? If there's any icing anywhere on the condensor, that's the point of restriction and it needs to be replaced.
Next, you should check the liquid line for restriction. Is there any icing along the line? Could an OT possibly have been inserted - or the line replaced with a line with a built in OT (a Ford thing)?
Speaking of OT's, are you using the correct one? The Ford # F5DZ-19D990-AB. Are you installing it in the evaporator INLET with the long end pointed towards the inlet opening (small end goes in first)?
Suction line could also be blocked as well.
Bottom lne is the pressure on the low side is too low, and hence the cycling. We need to find out what's dropping the low side so much... charge level, restriction, wrong parts / improperly installed.
By the way, you've done pretty much what most any tech would've done under the circumstances - nice work, well done.
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