ac operation check. are these pressures normal?

[trozei123]

ok, this has officially stumped me and I could use the experts on here for verification. here's the story.

my 92 explorer has not had working ac very long. everytime I have tried to fix it, it always seems to fail. the only parts that have been replaced are the ac compressor cycling switch (i assume that's what its called that is attached to the accumulator) and the orifice tube. everything else is original as far as I know. I have enough r134a in the system to make the compressor kick on, and cycle off. I don't want to add too much refrigerant, so I only have about 18-20 oz in the system.

now for my quandary...

my ac pressures are not seeming to make sense. when I first hook up the gauge set and get a reading with the engine off, the low side reads about 55 psi and the high side reads about 90. this is with the engine cold and the ambient temp outside of 78 degrees. when I turn the ac on, the compressor kicks on and the low side comes down to 20 psi. once that happens, the compressor will shut off as the pressure goes back up to 40. after that, the compressor will come back on, and repeat the same procedure. while all this is going on, the high side comes up to about 125 psi with the compressor on. when it shuts off, the high side drops down to about 75 or so. then the compressor will come back on, and the same procedure happens. my vent temps are showing 41 degrees, which does show that the system is cooling.

my big question is does this cycle sound normal? I am testing this in the evening with hopes that it will make figuring out this issue easier so I have normal running ac for the hot days ahead. I still have about 4-6 oz in the can of refrigerant, but I am unsure of the capacity and I don't want to risk overfilling the system.

 

[974X4BLACKSPORT]

Do a google search "r134 pressure chart" lots of info, too much to list here.

I will say that your pressures are low.

 

[trozei123]

I have now found a pressure chart. For that temp, the low side should be 35-45 and the high side should be 150-175. I see that the high side is indeed low, but are these pressures supposed to be when the ac is not running or when the compressor kicks on? I'm still confused because the pressures change when the compressor kicks on.

 

[974X4BLACKSPORT]

The A/C pressures are always checked when the compressor is engaged.

 

[trozei123]

i went ahead and added the rest of the can. that brought things up a little. now the low side kicks on at 45 and drops down to 20, shutting the compressor off. the high side builds to 175 with the compressor on and drops to about 125 after it shuts off. are these trucks supposed to cycle like this? most other cars i see have their compressors run for quite a bit longer, and the pressures do not move at all.

 

[92exp4x4]

i went ahead and added the rest of the can. that brought things up a little. now the low side kicks on at 45 and drops down to 20, shutting the compressor off. the high side builds to 175 with the compressor on and drops to about 125 after it shuts off. are these trucks supposed to cycle like this? most other cars i see have their compressors run for quite a bit longer, and the pressures do not move at all.

That's about right. Those are the numbers I aim for when setting my systems up. Sometimes the high side will run above 200 but not by much.

Keep in mind that the ac won't perform it's best on the 134. The system was designed to use 12 and Explores didn't use 134 until the 94 model year.

For 94, Ford added several things to aid the AC system, as the system just doesn't have enough capacity to cool using 134. They put in a bypass valve at the heater core, put more seals at the radiator to force air through the condenser and some other minor things until they could redesign the system for the 95 model year.

 

[Centaurious]

I hope that if the engine is off for a while the pressures equalize to the same reading both high and low. If not you have a blockage somewhere in the high side.

That bypass valve is worth it's weight in gold. I regularly see vent temps in the 35 to 38 range.

 

[LG57]

What the manual says: Put a jumper wire in the connector for the pressure switch to keep the compressor running. Add refrigerant until you have 35 to 40 on the low side. Remove the jumper, plug in the connector to the pressure switch. Now you should have normal cycling of the compressor. And you should have the coldest air you're going to get. I'm an amateur but this worked for me. The pro's on here are the ones to listen to!

 

[trozei123]

i will check when the engine is cold and stable what the pressures are. If i recall correctly, the low side was around 70 or so, and the high was about that as well, but i will verify.

where can I find how to do that bypass valve option? where can i buy the part?

 

[MrQ]

That's about right. Those are the numbers I aim for when setting my systems up. Sometimes the high side will run above 200 but not by much.

Keep in mind that the ac won't perform it's best on the 134. The system was designed to use 12 and Explores didn't use 134 until the 94 model year.

For 94, Ford added several things to aid the AC system, as the system just doesn't have enough capacity to cool using 134. They put in a bypass valve at the heater core, put more seals at the radiator to force air through the condenser and some other minor things until they could redesign the system for the 95 model year.

My '93 was converted to r134a and it gets downright freezing in there and in Houston that's saying something (humidity is around 80-90% during the summer). Biggest thing that sucks is that you have to constantly pull air over the condenser in a first gen. At idle it really doesn't do well unless you have the HD fan clutch. The engine management doesn't compensate enough for the A/C compressor pressure load needed for R134a. Engine really struggles at idle to keep the RPM's up.

 

[LG57]

Your pressures should equalize when the engine is off. If they don't, there is a blockage in the system. Did you flush the system when you changed the orifice tube? If not, the the orifice tube may be blocked again.

 

[trozei123]

i did check again, and the pressures are equal now when the engine is cold. i did not flush the system when i replaced the orifice tube as the original one came out clean. i just replaced it for peace of mind after I saw one youtube video explaining the infamous "ford black death". so far, the ac is working well. even though i have not driven it during the day to really test it out, (i work graveyard, so i drive when its cooler outside) i am pleased that things are still holding on.

where can i read up about whatever that bypass setup is? will that really aid in the ac performance?

 

[trozei123]

sigh. this explorer ac is kicking my butt. the ac only lasted about three days. now the compressor is cycling really fast. i am pretty sure that means that the refrigerant all leaked out. what is weird is that I have dealt with this ac three times now and have put a vacuum on the system each time. and every single time, even increasing the time of letting it sit from 30 min to over an hour, the vacuum holds. i asked a mechanic in the area and he claims that most likely it is going to be the evaporator has gone out. but several people on here have claimed that the evaporators rarely poop out and the most likely candidate is the accumulator. is there a way to check if the accumulator is the culprit? i am just puzzled by the fact that it holds vacuum fine, but then leaks out the refrigerant. could it also be the caps on the pressure ports?

 

[MrQ]

The Schrader valves in the connection ports could be bad; easy and cheap to replace. You wouldn't be able to tell if they were leaking because your gauges are still attached. Seems the most likely culprit.

 

[Centaurious]

Get a cheap AC sniffer then charge the system. With the gauges removed and the engine off start running the probe tip over every hose, connection and switch. Inside the truck turn on the blower to low and probe the vents. Run the probe tip over every inch of the condenser and between the condenser and the radiator. I found leaks where the hose entered the crimped fittings.

I had to replace both hose assemblies due to black death and leaks. Flushing both cores and blowing them out with compressed air is strongly recommended after this happens.

 

[markhenry63]

This is somewhat related...I have a 94 that has a busted in-line sight glass. Does anyone know where to get these? I don't know if it was an aftermarket add-on since I don't see it in any parts list for the system...Need to replace it before I can vacuum/charge the system.

 

[92exp4x4]

This is somewhat related...I have a 94 that has a busted in-line sight glass. Does anyone know where to get these? I don't know if it was an aftermarket add-on since I don't see it in any parts list for the system...Need to replace it before I can vacuum/charge the system.

I'd say that's aftermarket. I have never seen a sight glass on an explorer, or any other ford of that era for that matter. Where is the sight glass at?

 

[markhenry63]

I'd say that's aftermarket. I have never seen a sight glass on an explorer, or any other ford of that era for that matter. Where is the sight glass at?

It is inline coming from the condenser coils just inside the engine compartment. It sticks up off the line about 1.5 inches with a hex head on it and a small site glass in the center. I used to be able to see fluid moving through it then I noticed leak tracer on top of it one day and could no longer see the site glass. It is evidently a very slow leak as it hasn't affected cooling yet...