The air conditioner compressor on my 2000 S-10 would not run. I added 2 cans of 134a and changed the low pressure switch. Now the compressor will not cycle off and on and everything frost's up. The low side pressure is at 30 lbs when running and over 100 when I shut the air conditioner off. What causes the compressor to cycle when it is working properly? Do I have too much refrigerant in the system?

The low pressure switch turns on appox 26 psi. If the pressure is lower than that, it wont work, you have a leak.

BOTH High and low readings should be checked to have a better idea of what is going on with an AC system but based on the limited information… the compressor is not engaged or is not pumping. Below are some things I would check;

1. Check the high and low gauge readings with the AC on & set on MAX/Recirculate, middle vents with the engine at 2,000 RPM’s, blower speed on high.

2. Check the vent temperatures with a thermometer from the middle vents, far right & far left vents?

3. What is the outside temperature at the time the readings were taken?
4. Check to see if the condenser fan blowing strong?

5. Notice if compressor clutch is cylcling excessively.
Could be overcharged, not enough air going across condenser fins, compressor not pumping sufficiently… BOTH gauge readings are really needed to get a better idea.
Below are normal car AC pressure readings with 134A.

Normal readings on high and low side with AC OFF (static pressure) – Depends on outside temperature, but normally is between 80-105 PSI

Normal low side reading with AC on high speed and MAX & engine at 800-1000 RPM’s – Ranges from 25-35 PSI

Normal high side reading ranges from 200-350 PSI

Don’t assume that if adding little Freon is good that adding a lot is better! Overcharging just a little can decrease the performance of the system and possibly damage the compressor

Thank you for using fixya and good luck, keep me posted. Be glad to help you get your A/C running again soon.

The AC compressor does not have to be running to charge the AC system, and the low pressure switch will even prevent the AC compressor from operating until there is sufficient pressure to operate the AC compressor without damaging it.

Start the engine and turn on the AC, then charge the system with the R-134a and as soon as there is enough pressure built up to trip the low pressure switch off, the AC compressor clutch should then engage and then finish charging the AC system.

Before you add freon to measure how much freon is clucht checks if the compressor is activated when you connect the air conditioner if the clucht not activated and have a good pressure in the system looks at low pressure switch that goes in the drier and that very often these are damaged, you also have to check the fuse and relay the compresor.Thanks

If it is a quick connect fitting, it is R-134a
The low(charge) side fitting is: 13mm
The high side fitting is: 16mm

If it is a threaded fitting with threads on the outside, then it is the older R-12 refrigerant and can only be serviced by a licensed air conditioning service.

The low(charge) side is 7/16" threads
The high side is 3/8" threads

When servicing your air conditioner it is best if you have gauges, but it can be done without, just be careful.

Assuming the air works, but just not putting out that much cool air, then 1 or 2 cans of refrigerant won't hurt.

If there is no pressure/refrigerant in the system at all then it is usually a sign of a leak and should be taken to a pro because you may need to replace the receiver/dryer and have the leak fixed. The system needs to be evacuated for maximum efficiency if there was a leak or if hte system has been opened.

Adding too much refrigerant can be catastrophic as the high side pressures can reach 200-300psi on a hot day. So if you happen to have a low side gauge, and it reads somewhere between 35-45 with the Ac operating, you are golden.(tire gauge won't work)

Don't be surprised if the compressor doesn't kick on right away. Some vehicles are equipped with a pressure switch to keep from damaging the compressor if it runs low. Usually after adding one can, it is enough to engage the compressor.

Hope this helps.

Mark

No,you won't find it in the owner's manual. It charges through the low pressure side,which is the larger of the 2 available ports. You can't hook it up wrong. I suggest you buy a Hayne's manual for the truck. It has 90% of any answer you might need. A/C can be tricky to fix for the novice. If charging doesn't work,take it to the shop.

it is the low pressure switch trying to save the compressor. the system is low on refrigant. on this ford it should be R-134a all new cars are that refrigant.

you should be adding the 134a to the system the low pressure switch is doing its job by not allowing the compressor to kick on, it wont kick on until there is enough 134a in the system to be above the preset pressure for the low pressure switch.

The system could be low on oil. The compressor will shut itself down if it detects a lack of oil or refrigerant. Try adding compressor oil (comes in a can similar to the R-134A) to see if the compressor will stay engaged long enough to accept a charge. It's also possible that the system has so much air in it that it needs to be evacuated before refrigerant can be added. I'd try to add the oil and see if you have better sucess adding refrigerant REMINDER: Have AC on HIGH when adding refrigerant with car running

Hope this helps with your AC problem. Please post back with any other questions. Best of luck.
Greg

you are probably low on freon again. If the system is low, the pressure switch won't turn on the compressor. Add a can of R134A using a hose that has a gauge on it. It should read in the "Good" area if you have enough freon. Adding a can will probably be enough to start it working. If so, look for a leak somewhere, usually around connections where O rings leak.
You will see some oil spotting where the leak is.