Corolla A/C cycling intervals

The A/C condenser on my '95 Toyota Corolla had a leak so I got it replaced. The shop also replaced the receiver-drier. Now the A/C compressor seems to cycle on/off more frequently (about 10 seconds on/off) at idle with the fan on low. Can anyone tell if this is normal? What are normal cycling times for a car's A/C in general?

Reply to
Dan
Loading thread data ...

It sounds a bit too frequently. Cycle time is usually determined by temperature and or pressure limits. You need to take it back and show them the problem. It may be an evaporator temp sensor switch, OAT temp is just low so it cycles fewer times, a pressure switch in the A/C loop is defective, I know this is not much help but it's difficult to tell without testing. Good luck.

Reply to
user

Did they check the R134a level after they replaced everything? Sounds like you could be a bit low.

Charles of Schaumburg

Reply to
n5hsr

If it is cool/cold out, the more frequent cycling can be normal.

Reply to
maxwedge

10 second cycles for the AC compressor is too often. Bring the car back to the shop and have them repair their mistake, which could be insufficient evacuation before adding the refrigerant, or too much refrigerant.
Reply to
Ray O

Thanks. One more input: I looked through the small glass window on top of the receiver-drier while the compressor was cycling. When compressor is on, I can see fluid (with some bubbles) flowing by. When it's turned off, the fluid flow stops. Is this ok?

Reply to
Dan

That small glass window is referred to as a "site glass". If you see bubbles in the site glass with the compressor running, it is low on freon, which is causing the over excessive cycling. When the system is fully charged, the site glass should be clear. They didn't put enough freon in, or you still have a leak.

Reply to
dahpater

The OP has yet to tell us what the ambient temperature is. Cycling and bubbles in a sight glass are normal at low temperatures. Cycling is normal if the blower speed is turned down. Bubbles are typical of HC-134 systems also. This is why almost no modern systems have a sight glass. A 95 Corolla uses HC-134 unless some bogus fluid has been put in. I'm surprised it even has a sight glass. Perhaps this is an add-on system?

The only truly accurate way to know if the refrigerant charge is correct would be to evacuate and recharge with the refrigerant weighed. Proper evaluation of performance would have to do be done with outside temperature greater than 70* f. If outside temperatures are high, the blower speed is set on high, the AC does not cool well and the compressor clutch is cycling it would be likely that the refrigerant charge is incorrect. But even then, this could be a bad expansion valve. Another cause of cycling would be a faulty condensor/radiator fan and poor air-flow through the condensor. This will cause cycling at idle but not at highway speeds due to excess high-side pressures.

The OP has not provided nearly enough information for a diagnosis -- if, indeed, there is any problem to diagnose in the first place. Don

formatting link

Reply to
Don

Hi,

The refrigerant type on this car is R134a (stated on a sticker) and I believe that's what they filled the A/C with at the shop. The site glass came with the car. Indeed, I checked the site glass when the temperature ouside was around 70F, and it wasn't too warm inside the car either.

--D.

Reply to
Dan

The small glass window on top of the receiver/drier is called the *sight* (not "site") glass. Most Toyotas, even with R134-A, have them.

When the compressor is on, you should see fluid flowing by when the compressor is engaged. It is OK to see some bubbles, but you should not see anything that looks like foam flowing past. If you see foam, the system is low on refrigerant.

At 70 degrees ambient temperature, the system should cycle quickly, but not every 10 seconds.

If the system was not properly evacuated prior to charging, moisture could remain in the system, especially if it was open to atmosphere for a long time. The moisture can cause icing in the expansion valve, causing excessive high-side pressure. As the pressure rises, the compressor will disengage, the ice melts, and it starts over again. A bad expansion valve can cause the same symptoms, as can icing on the evaporator.

To diagnose the problem, a shop will have to install AC pressure gauges to see what is happening, and review their notes (hopefully they keep shop notes) to see how long they evacuated the system and how much refrigerant by weight they installed.

Reply to
Ray O

I knew that. 1994 up HC-134 is standard on most vehicles.

It should have been, but a few people use bogus "alternative" refrigerants.

Did you buy the car new? Do you know if it has factory or add-on AC?

Don

formatting link

What was the temperature of the air coming out of the vents? What did you have the blower speed set at?

Reply to
Don

I didn't buy the car new, but I know the A/C was original. I didn't check the exact temperature out of the vents, the air coming out feels pretty cold, especially when the compressor is engaged. The blower speed was on low. For how long should the system be vacuumed out before filling with refrigerant?

Reply to
Dan

Cycling could be normal. At low blower speed the compressor has to cycle off frequently to prevent the evaporator from freezing up. Hot weather and a car that has been closed up for a few hours in direct sunlight will tell you if the system is working well.

If the system has been open -- parts replaced -- 1/2 hour absolute minimum. Longer if its cold or humidity is high.

Don

formatting link

Reply to
Don

By 1994, most Toyota AC systems were factory installed. If the air is cold when the compressor is engaged, then there is probably sufficient refrigerant. Evacuating the system should take at least 15 minutes.

Reply to
Ray O

It's most likely cycling off on the evaporator temp. If the weather is not hot that would be normal if there is no heat load. When the weather is cool and your fan is on low speed there is not much of a heat load and if the compressor does not cycle off the evaporator will freeze up.

As a performance test it should meet these conditions.

engine hood closed Engine rpm at least 1,500 all windows open recirclate off fan speed on high temp setting at coolest vents setting at upper vents all vents open outside air temp. = 75f - 90f degree. compressor cycle off = supply air temp about 35f - 42f degree. compressor cycle time = varies

Generally speaking the compressor should be cycling on/off at the same supply (vent) air tempature. Fan speed and air tempature will effect compressor cycle rate. If the weather is hot enough or the engine RPM is low enough the tempature at the vent may be warmer.

Good luck Dan

BTW: do not charge 134a systems by the sight glass.

Reply to
Danny G.

Damm. Some how missed most of this thread before typing all that. 8/

Reply to
Danny G.

Well, it seems to work OK after all. With fan speed on highest, compressor is on for a longer time and I can see a constant refrigerant flow in the sight glass.

Thanks all for your inputs. :)

Reply to
Dan

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.