Just got the A/C working on the 92 Civic. Replaced the ECU (with used one). Converted from R12 to R134 (New compressor etc). Today (100 Degrees) at 80 mph the A/C cycled on/off alot (every 3-15 seconds). Around town it is doing the same thing. When I let it sit in the driveway and idle it cycles less often and as a result does get colder. Does this sound normal?

Thanks

 

Any Ideas???

 

I am not getting any ideas here so let me run this one by you. On the highway it ran fine today (102 degrees). When I get into town and slow down it starts to cycle off/on alot or not come on at all. Is the extra A/C fan designed to run at certain temps only or when ever the A/C in ON? Also, is it possible that even though the A/C fan appears to be running that it could be running slower than needed thus requiring the Compressor to turn OFF more often?

Some feedback would be appreciated.

 

You really need gauges to tell. but a can from the outo parts store has one cheap. quick try, remove a little freon, sounds like you overcharged it a tad. get back to us with results. Low side should be arround 25-55 depending on ambient temps and humidity etc, the return line (fat tube) to the compressor should be cold if its about right.

 

Thanks

I had the conversion to 134 done last month and had an ECU issue. Since we resolved that I do not know if they checked the pressure again. I will run it by the shop tomorrow.

Thanks for the feedback
Greg

 

Update

Took the car by the mechanic and it appears that the fan is not running consistanlty. It stays off more than on thus allowing for higher temps and the high pressure cut off is turning the compressor off. He is going to hot wire the fan straight to the A/C switch.

Hope that works.

 

Most condenser cooling fans are on all the time the compressor is running, so his mod will probably work unless there is another problem causing high pressures or condenser temps. A simple jumber from the compressor realy to the fan realy is all that's needed.
Did he check the pressures with the fan hot wired yet ? What are they ? at what ambient temperatures, running at 1500rpm in your driveway ? if it still cuts in/out, try spraying the condenser with a hose, see if it works better.
Let's have some more feedback after the fan mod.

 

I am hoping he does the mod on Friday. I will get him to put the gages on it then. I will be sure to let you know what happens.

Thanks for the advice

 

Sounds completely normal to me. Head pressures should be around 180psi high side, 35 low. If the low side is significantly lower than 35 your system is undercharged.

If the vent temperature is above 50 degrees I would be concerned of low refrigerant. A low refrigerant level will cause the evaporator to ice up, along with the metering valve, causing the high side pressure to rocket up, and cycle the clutch.

Typical clutch cycle times are about 4-8 seconds on first engagement. That is until; the cab is brought to temperature, once it is fully cooled, the clutch will cycle faster, at around 2-3 or so seconds. This is because there is no heat to remove, and the evaporator begins to frost over, again, rushing head pressures to cut off the compressor.

To really figure out if your are undercharged, a low side gauge will be needed. Both help a lot, but if the low side is too low, your charge is most likely low. A low high side can indicate many things. Among them are:

Worn metering valve
Excess airflow over the condenser (A good thing)
Poor compressor output (REALLY BAD)
Low refrigerant charge

 

find out at what pressure the system is cutting out at. on a 92 style the fan runs from the factory whenever the compressor is on. they don't have it sophisticated where it waits to turn on when the pressure is high. if the compressor is turning off at the wrong pressure, assuming the charge level is correct, then one of the switches has lost its range as to when it should open or close. personally i have a 98 civic,a nd it runs as stated above, and the compressor runs until the low side pressure gets to 25-30 then it waits until about 50 -55 psi to come back on. depending on the ambient i have seen high side pressure of 225 to 350 but it still switches at the same low side. so find out your pressure and let us know what the rpm is when you got the readings, it should be performed at 1500. if it keeps cycling it sounds like its undercharged overall. i guess a good first step to take would be to recover the stuff in the car, and see how much is in there compared to what the charge should be. keep in mind most 134 conversions dont perforrm as well as when they had r-12. and overall tell the mechaninc guy to not hot wire any fans, it should operate fine as honda designed. making the fan run more than when its commanded wont help, when it is commanded, its 100% speed. its not variable. so if the fan is on when the compressor is off, that all youll get as a difference. it will run the fan ahrder than designed, and be a more constant heavy load on the alternator. either way having the fan run when the r-134 isnt flowing wont help you. overall, i do know it should cycle less often when idling. due to less output from idle speed. it sounds like at high speed either its cutting out due to high side too high or low too low, i need to see actual pressures to further help

 

Another source of compressor cycling is the evap thermostat, it will cycle on low coil temperature if the system is undercharged to stop icing, it wil also cycle if the system is normal and the vent supply temp gets lower than 40f but that is normal. Low pressure cut of on a typical honda is below 20psi for more than 60 seconds.

 

OK

I have the fan running full time and it still cycles a lot in town. Enough it does not stay on long enought to actually cool the car. I was told that there are pressure relays and a pressure sensor in the cabin. Any ideas as to if these could be the issue? Where they are and where I can get new ones?

Thanks

 

quick cycling usually means its overcharged...

or a bad switch...

diagnosis murder

 

By Switch do you meanthe pressure switch?

Thanks for the responce

 

yeah i bad high pressure switch could make it cycle faster.

hook it up to gauges and see what kinda numbers it makes. thats about the best way to start, then go from there

no problem