Diagnosing A/C blowing warm on my 2003 Ford Explorer

Last summer I noticed that my 2003 Explorer was not cooling off as well as usual on hot days but most of the time the A/C worked reasonably well so I didn't bother doing anything about it. After it cooled off I didn't think much of it until this spring when I noticed the A/C blowing warm when it got up into the 80s. When idling I could hear the compressor clutch cycling on and off, which is a telltale sign of a low refrigerant charge. The system is designed such that if the suction side of the A/C system drops below 20 PSI or so, a cutoff switch will disengage the air conditioner clutch. If the compressor was allowed to run on a low refrigerant charge, the compressor would not receive enough oil flow, and it would subsequently fail from a lack of lubrication. When you notice this happening it's a good idea to discontinue use of the A/C system until you can service it, to avoid wear and tear on the compressor. Besides, the A/C really isn't really cooling at that point anyway.

As with most jobs these days, it seems that doing it myself costs about the same as paying my mechanic to do it -- only instead of the money going to my mechanic, it goes into my tool box after the job is over! My hope that I will eventually save money by re-using the new tools for another job. So far that hasn't worked out for me, but my brother-in-law has sure saved a pile of cash when I've helped him fix his cars!

I watched a few videos watched on YouTube, and read a few threads on the online forums before I decided to add a manifold gauge set to my arsenal for $60 from Amazon to tackle this myself. While I was at it, I picked up a $7 brass can tap, as the cheap plastic ones they sell at AutoZone don't look like they would hold up over time. I picked up a can of R-134 compatible refrigerant at my local Harbor Freight while stocking up on tools for an upcoming plug job and fuel filter replacement on my 2006 Saturn. I'm sure I'll have some amusing tales to share from that project... Anyway, I chose a brand specifically designed for topping up the system which has a small amount of oil in it as well as a pH buffer to neutralize any acid that may be forming in the system if there is a slow leak.

I began the job by attaching the hoses to the corresponding gauges in my manifold kit. Blue hose to blue gauge (cold / low pressure side), red hose to red gauge (hot / high pressure side). The flare fittings provide a tight fit by barely tightening finger tight. To the center I attached the yellow fill hose. I then made sure the valves on both sides were closed, and hung the manifold from the hood latch using the hook.

Starting from the condenser coil, which is always located adjacent to the radiator, I traced the coolant line back toward the engine until I found the high pressure valve. The cap was dirty so I hit it with some brake cleaner and wiped it off before taking it off. Being careful not to lose the O-ring which stuck to the top of the Schrader valve, which I carefully put back into the cap, I attached the high pressure side (red hose) fitting by just pushing it on. Then I looked under the engine for an insulated line coming out of the firewall -- that's the cold line running condensed liquid out to the evaporator which is behind the glove box. Adjacent to it I located the return line from the evaporator which I traced to the accumulator, where I found the low pressure side Schrader valve. This cap was clean so I unscrewed it and attached the low pressure disconnect fitting (to the blue hose) again by pushing it on. Both gauges were reading about 90 PSI and I heard no hissing, so confident my manifold setup was solid I started the engine, turned the A/C on full blast, and checked the output.

Low reading on high and low sides with compressor engaged

When I could hear the compressor clutch kick in, the low side was reading about 24 PSI and would slowly drop to 19 PSI before the compressor would cut out. The high side was reading 130 PSI and would increase to 140 PSI when the compressor would cut out.


Since both low and high sides were reading well below the recommended range, I determined that the system was low on refrigerant. There are a lot of rubber lines on this system (thanks, Ford), and it was last serviced four years ago after a compressor clutch failed resulting in a total evac. Since it was still barely functioning at this point, and had working but low pressure on it, I don't have any reason to believe there is a significant leak, otherwise I would have stopped there and gone down the path of looking for the leak.

Air is the enemy of the A/C system; you want to keep it out! The manifold setup started with air in all the lines, so prior to filling, it needed to be purged. To do this I started by assembling the can adapter and the can. I opened my can adapter valve all the way, retracting the pin; then I screwed it onto the can tightly, and closed the valve. I attached the valve to the manifold inlet hose (yellow). To purge the inlet hose I unscrewed it a couple of turns at the manifold, and slowly cracked open the can valve until I heard hissing, counted to two, and then shut it. Then I slowly opened the valve on the blue / low side until I could hear a hissing sound, counted to two, and shut it. I then (quickly) tightened the hose connection at the manifold. With the air purged from the blue and yellow hoses, I was ready to start filling.

Closer to normal readings after adding one can of refrigerant

Filling is rather simple; just open the valve on the can, followed by the valve on the blue / cold side, and gently rock the can while watching the high pressure gauge. As the liquid in the can boils, vapor moves up the yellow tube, through the blue tube, and into the A/C accumulator. Every minute of the fill I could see it rise about 5-10 PSI until the can was empty, about 15 minutes. Filling goes significantly faster in the beginning because the can is hot; once it gets cold, the liquid doesn't boil as rapidly within the can. By the time I finished filling the can was VERY cold -- it even had some frost on it. Gloves (and safety glasses) are a necessity for this job to protect from the extreme cold. At this point, the high side was running at 180 PSI and the low side at around 36 PSI steady with no compressor cycling.

The Explorer is a bit peculiar in that it actually has two evaporator coils, one in the front, and one in the rear. When you turn the overhead console fan knob on, the second evaporator coil begins to function, and the system pressure changes. In this mode, the low side was running around 45 PSI and high around 215 PSI. That is close to the optimal R-134 range. It could probably use a few more ounces but since the can is empty I will just wait until I do another A/C system top-up to give this one a few extra ounces of bump. In retrospect I should have charged with both evaporator coils running but at the time I started I didn't think about it. I'm just glad I didn't accidentally overcharge the A/C system as a result. This potential pitfall is NOT mentioned in the Haynes Repair Manual.

My Explorer is an Eddie Bauer so the climate controls are the same as the Limited -- it shows the outside temperature. The probe is located just in front of the condenser coils so this makes the A/C test simple. I stuck my thermometer in the center vent, put the fan on low, and waited a few minutes. The thermometer read 50*F and the outside temp (at the condenser) 87*F for a 37 degree drop. That's within spec for R-134 so I'm quite pleased with the results. My drive tomorrow will be much more pleasant than this afternoon was.

My mechanic would have charged me $79.95 for the "check-up", plus $20 per pound of refrigerant and tax. That would have added up to around $110. I did this job myself, including tools I will re-use on my other cars, for $90. I actually saved money this time. Even better, it took me a half hour. I can't get my mechanic to complete an oil change in a half hour. I would have been waiting two hours for them to complete this job, so I saved time AND money. Win win!

A 37*F drop at center console -- not bad!

I'm not quite done battling it out with the climate control system on this vehicle. Both actuators in the rear are broken (the design has a known flaw that leads to failures after 5-7 years), and the A/C recirc door actuator no longer works, so the A/C always draws in fresh air. That is fine now but when it's July that won't be so nice. I hope to get to repairing those soon.