Well it's finally summer time and I decided to kick on my A/C. It blew cold [not freezing but cold], but I noticed that my compressor would cycle on and off more than 1 time a minute. From what I've searched it appears that the compressor is SUPPOSED to cycle until it reaches a certain pressure, rinse, lather, and repeat. I've also read that low freon may be the cause of this. So I invested in a recharge kit; good ol' ES-12a industrial. So I recharged my A/C and boy did it blow cold! They gave me a nice lil thermostat to put in my vent to see how cold it blows. So now my A/C blows 40* but it still cycles. I drove for give or take and hour and a half today and noticed that it cycles on for 15 seconds, then off for 5 repeatedly. Blows super cold but just seems like it cycles a bit often. Is this normal? I searched through the FSM in section G of the body troubleshooting and it had no fault trees for a cycling compressor. It shows you how to properly check refrigerant in the system and I appear to have the right amount [sight glass is lightly cloudy, definitely not WHITE but lightly cloudy with no bubbles]. Pressures seem to be off though, slightly high actually on the low side. The FSM states that pressures should be about 22-28 psi @2000 RPMs. They're closer to 33 give or take some. Have I overcharged the system or does it still require some more freon? The FSM states vaguely, the proper refrigerant amount. It says that while running it should be clear in the sight glass, yet that condition may be "too much or proper refrigerant". LOL I think its kinda funny anyway. That's on page G-26 in the 1994 body troubleshooting manual. I am also running the STOCK ECU.

So I guess my questions boil down to this:

Do you think I need to charge it some more or "relieve" some of it properly IAW EPA standards?

Should it cycle less often or am I worrying too much?

Should I just shut up and enjoy my 40* A/C?

Thanks for your thoughts,
Matt

 

Your A/C is fine. If you are blowing 40 degree air from your vents you are golden....what is the ambient air temperature? Your A/C system is designed to cycle the ac compressor....once your evaporator hits a certain temp it will shut off the compressor to avoid the evaporator from icing over.

Shut up and enjoy your cold air.

 

The ambient temp is 108 actually :P. I was sort of thinking about that too, the evaporator icing I mean. This ES-12A stuff is some awesome stuff but if I'm blowing 40* air I can't imagine what the actual components are experiencing. Thanks for your opinion!

Matt

 

agreed -- if you are blowing 40 or below, that's the way it should be working.

Might check your fans though, it doesn't say this anywhere, but if one of your fans is not working ( I forget which one), the a/c will do some crazy things trying to stay on temp.

 

Good point I might check that. I've also heard that clogged condenser fins or just having leaves and junk in there can do some crazy things as well.

 

You are cycling to much. Do you access to gauges, 33 psi on the low side is low for 108 degrees. I would guess that you should be in the 50-60 range and the high side around 275ish. Is the low side steady at 33 or does it get down to 33 then kick out the clutch? I guessing your a little low still but more info would be helpful.

 

When I recharged it, the more freon I added the higher the pressure went. This is an R12 system not an r134. The r134 does run at higher pressures.

As to when my compressor kicks off, I'll have to do further testing on that. When I charged it, it did not cycle. It wasn't until the system ran for about 15 min of driving that it began to cycle a lot. If it cycles on my way home I'll hook up my pressure gauge and see what I can come up with for numbers.
Matt

 

Do you know how many OZ. of refrigerant you put into the system?


From the manufactures website....http://autorefrigerants.com/co00033.htm


It is possible you overcharged the system and the system is cycling because of high pressure on the high side of the system.

 

Good catch RenesisFD. I used 1 can to recharge it. The capacity of my R12 system according to the underhood sticker is 1lb 5.2 oz or 21.2oz. It is possible I overcharged it. But it also does not explain why it was cycling prior to me charging it. UNLESS...it was low on freon and cycling, then I overcharged it and caused it to further cycle..Ugh I hate AC systems...I'm gonna recheck my pressures and get them into spec with the FSM and see what happens. I'll keep you posted.

Matt

 

^ I did not see any mention of what the high side pressures are. Do you have a gauge to check that?



I do not think you have a problem with your fans because you do not mention overheating problems and you are running the car in ambient temps above 100 degrees Fahrenheit.


So if I am understanding this correctly... You were having cycling issues so you added a full can of refrigerant to the system that already had refrigerant in the system?

 

You are understanding correctly I had a condition in which my compressor was cycling at idle and while driving previously and chalked it up to low freon. So I purchased a recharge kit of ES-12a and emptied a can into it. A/C blows cold, does not cycle at idle any longer.

Now I just got done on a nice pleasant drive around base doing errands. Here are my new findings and theories.

A/C does NOT cycle at idle. Low side pressure while the compressor is running is 30 PSI [Possibly a crappy gauge as well] @2000RPM [FSM spec is 22-28 PSI]. Driving around, A/C blows around 48* and does not cycle the entire time. A/C never reached 40* like it did on my highway driving. New theory is as follows. ES-12a industrial refrigerant is some intense stuff. Freon travels through system and into evaporator where it does its A/C stuff [forgive me I'm no expert]. Now my A/C is blowing at 40* when its running on the highway and that's pretty cold if you ask me. Freezing point is 32*. In the evaporator is a Thermoswitch as the FSM states that regulates the compressor on and off to control the system just above freezing to prevent icing and blockage of flow. Now, if this ES-12a stuff is so intense that its causing my A/C to blow TOO cold, the thermoswitch flicks the compressor off until the evaporator is to above icing temp [approx 5 seconds]. Thermoswitch detects the icing condition is no longer apparent and kicks the compressor back on. Approx 15 seconds later icing conditions become apparent and the thermoswitch kicks the compressor back off.

The reason I believe this is because it only cycles when it blows at 40* [8* above freezing]. So by properly evacuating a small amount of freon I can reduce A/C temps to closer to 48* and not have the issue of the thermoswitch kicking on and off the compressor. Now to test this theory as a FOR SURE condition of whats happening, when I find the time this weekend I will trace the harness for my thermoswitch and monitor the voltage using my How-Ya-Doin' and see if that is indeed the component cycling on and off my compressor. I will post results this weekend.

Thanks for your help and opinions!
Matt

 

-Update-
My theory is starting to look better. On the drive home today my I observed my vent outlet temps. The compressor did not cycle at all...until outlet temps reached 40* then it began to cycle off for 5 seconds and on for 15 seconds. I turned down the coolness **** and as soon as my vent outlets went above 50* or so it stopped cycling. I put it back to max cool so I could verify low side pressures when I got home. Low and behold my pressure @2000rpm was 25! Within FSM spec! So my compressor only cycles when outlet temps are 40*. I'm going to monitor voltage on my thermoswitch next chance I get and see if that is what is triggering my on/off condition.

 

-Final Update-

Theory confirmed. My thermoswitch is indeed disconnecting at 40* outlet temps. I back-probed the thermoswitch and monitored continuity on the green and green/red terminals [switch side] and observed a disconnection at 40* temps that cycled my A/C. Low side pressure reading again 25 psi @ 2000RPM.

Facts

The Air Conditioning system is designed with 2 shut offs for the compressor; a refrigerant pressure switch and a thermoswitch located on the evaporator. Page G-8 in the 1994 Body Troubleshooting FSM states the thermoswitch opens and closes based on evaporator temperature and regulates evaporator temps just above freezing to prevent icing and blockage of airflow. The refrigerant pressure switch cycles if pressures are out of spec to prevent damage to components. Page G-48 shows a graph of relative humidity and VENT OUTLET temps being at COLDEST ~50* during the performance test.

R12 vs ES-12a INDUSTRIAL

R12 is what the 1993/1994 model RX7's came charged with. R12 has been phased out of vehicle A/C systems for its harmful attributes to the ozone. ES-12a is an environmentally safe substitute for anyone not looking to convert to r134a. ES-12a is also a "better" refrigerant that R12. Now here are the MSDS facts:

R12:

Boiling point: -21.6
Freezing point: -252*

ES-12a:

Boiling point: -36.1*
Freezing point: -286*

ES-12a has a lower freezing point and a lower boiling point making ES-12a the more efficient refrigerant. However possibly TOO efficient.

With R12 our A/C should blow ~50*. With ES-12a mine blows 40*. The evaporator temps are lower allowing for lower vent temps. The thermoswitch is viewing the evaporator and regulating it "above freezing". Freezing point of water is 32* so slightly above that would be give or take 40*! So now what is going on here is my thermoswitch and A/C system are operating to FSM spec just as designed. The evaporator gets near freezing points and the thermoswitch kills the magnetic clutch on the compressor. Temperatures increase and the thermoswitch allows the clutch to re engage. The compressor does its thing and the evaporator temps begin to plummet again. Thermoswitch sees the freezing temp and once again disengages the clutch. Rinse, lather, repeat.

Conclusion

ES-12a is a good substitute and indeed does cause my A/C to blow "super cold" as advertised. The only issue is because of its increased capabilities, it causes a more rapid cycle of the compressor. If I were to recharge my A/C again, I would probably stick to the REGULAR ES-12a and not grab the industrial. 40* is an awesome temp to have blowing out of my vents in this 100* heat but I could deal with 50* and a compressor that does not cycle so often.

I hope this helps people in the future with any troubleshooting and A/C recharge solutions!

Matt

 

For the reasons you mentioned above, Thats why I think you have the system overcharged. Hence why the manufacturer suggests you use less refrigerant.


If there is less refrigerant then the pressures will be closer together, this will make the low side temp higher and will help prevent the compressor from cycling.

 

RENESISFD,

Wouldn't reducing the amount of refrigerant alter my pressures? I thought there was a correlation of low refrigerant low pressure and high refrigerant high pressure. If this is the case then reducing refrigerant would caused pressures to go out of spec. The fsm is very vague on proper refrigerant content. The fsm only states that while running if your sight glass is clear them you have either too much or the proper amount of refrigerant. So my question is how exactly would I properly measure the amount of refrigerant iny system other than taking it somewhere to get it evacuated and recharged?

 

Measure the inlet and outlet temps of of the evap and condensor. This page has all the info you need Air Conditioning Temperature Basics. That is the best way, get your temps in line and the charge weight will be perfect.

 

There are 4 "shut offs" The ECU can also shut off the compressor, as does the button on the dash, but that one is obvious.

You are not reading the G-48 diagram correctly. It clearly states on the R-12 chart that it is the "TEMPERATURE DIFFERENCE BETWEEN INLET AND OUTLET" The chart is temperature delta, not vent output temps.

 

Yes (all other things being equal) and yes (in a properly functioning system).

Thing is, pressures are dependent on a whole mess of variables....compressor shaft speed, ambient temperature, ambient humidity, radiator fan and cabin blower performance, how many mashed fins and bugs are in the condenser, how many feathers, leaves and other assorted trash is in the evaporator core, etc.

The FSM lists the mass of refrigerant that should be in the system for R-12 and R-134a. Page G-45. Based on my experience, these numbers are for the Nippondenso system. There is (or was) a sticker on the underside of the hood indicating proper charge mass as well. MANA systems hold more.

Using the sightglass to arrive at the proper charge is perfectly valid for R-12. Clear the sightglass then add an ounce or two more for a decent amount of liquid in reserve in the drier.

You could also put the whole car on a super accurate scale and then release the charge and see how much less the car weighs.

 

Officially hate A/C systems. Got fed up with the cycling and started taking some more advice like I should. I have a slight hiss from under my glovebox which from research is the expansion valve. Now the thing is this hissing is continuous. I believe it should hiss at first and go away. So I have some plans for my A/C. Plans are as follows:

New Drier
New Expansion Valve
Get an air duster and clean out the fins of my condenser of all the crud
Rent a vacuum pump and A/C manifold gauge set
Grab some r12 mineral oil

I am trying to do this myself as no A/C places around me will deal with R12. They all want to retrofit me with r134a. I plan to evacuate the system and pull a vacuum on it. I found an awesome thread in the first gen section regarding DIY A/C recharging with all this fun stuff. Let me know if I'm missing anything or if you have any suggestions for other replacement parts!

Matt

 

All of the orings? Are you saying it was full of r12 and you mixed different refrigerant with it? If it had a low charge it would be smart to find the leak and fix it. Add some dye and run it for awhile.

 

I believe it was had some r12 in it and I charged it with an r12 substitute. I do plan on grabbing some UV dye and adding it in. I believe I have a freon leak at my expansion valve. I'll investigate it further when I invest in the ac manifold gauges and vacuum pump.