A/C Compressor cycles

[Michael Roberts]

Just finished replacing my Evaporator and Accumulator. System was vacuumed out, oiled and recharged.

I've noticed the compressor cycles off whenever I raise the throttle above idle.

Watching the gauges when the compressor is engaged, the low goes to about 35psi while the high goes to almost 200psi.

I wait for the compressor to engage, watch the high elevate to 190-200psi and the moment I move the throttle above idle the compressor disengages.

When the system is turned off (engine not running) and both sides reach equalibrium, there's 90-110psi on both sides. The reason for the variance here is I found it slowly increases as it settles. I assume this is the normal process of the gas change with temp.

The system is not as cold as I had thought it would be. Do you think I'm overcharged or not charged enough?

The opinions you find online seem to vary tremendously when it comes to what the pressures should be.

Any opinions would be helpful as I'm no expert with A/C.nline:

 

[scott degroot]

Why did you replace the evaporator? How much oil did you put back in? Did you flush out the entire system before adding oil? How much refrigerant did you put in? What is the low side pressure when the compressor kicks out?

 

[Michael Roberts]

Hi l1tech,

Evaporator was leaking, started smelling oil in the cab. Couldn't believe how dirty the evaporator was from debris. Dye I introduced earlier was on the fins.

I put 4 ounces back in. This was done with the little aeresol cans of PAG. First can was introduced with system vacuum, second was after system was up and running.

No I didn't flush the entire system out, but the filter on the orifice was quite clean looking as well as the oil that came out of the system.

I put three of the little cans of refrigerant in (can't remember how many ozs these are now) but some was left over in each of the two first bottles until I realized I needed to shake them to help them disperse.

Low side pressure was approximately 60psi when compressor disengages.

 

[scott degroot]

At 60 psi the compressor should be engaged not disengaging unless the high pressure cutoff switch is going open...what is the high side pressure when it cuts out?. First thing I would do is have the system pulled back down, vacuumed and then charged with the appropriate amount of refrigerant. Problem with using the cans to recharge is that while switching cans you actually end up getting alot of air in the system. Did the cnas have any oil in them?

 

[Michael Roberts]

l1tech,

The compressor cycles off whenever I raise the throttle above idle.

The compressor cycles normally at idle speed. The pressures at idle speed are 35 low, 190-200 high. If I then raise throttle above idle, the compressor immediately cycles off. If I hold the throttle at 1500 the cycles are then too frequent.

I don't think I have any air in the system because I used my brand new aluminum gauge set with an appropriate can tapping valve. Before introducing the refrigerant and lubricant I purged the air from the yellow hose to the manifold before charging.

The refrigerant cans do not say oil is included.

I put two cans of PAG oil in. These each contained 2ozs of oil and 1oz of 134a.

I have run my truck this morning after sitting for the weekend. The system seems to cycle normally at idle, but if I raise the rpm at all, it cycles off immediately and cycles too frequently above idle speed.

The service manual says: Oil capacity 9ozs. Refrigerant 30ozs.

 

[scott degroot]

Really sounds like it is low on refrigerant to me.

 

[Michael Roberts]

l1tech,

Yes you're right! I added most of another can of refrigerant today. It now cycles like it should. I guess not being an A/C pro, I didn't want to hasten to overfill the system.

Pressures when I was finshed were: 30-35psi low and 225psi high with compressor engaged and engine at 1500rpm.

I've noticed you have to be patient waiting for pressures because the refrigerant starts to change with different temps. That is, from the time you've dispersed it cold into a running system and when it settles inside with what's already being cycled.

I'm now listening to my compressor. It may be a little more noisy than it should be. Ah well, that'll be another post I guess.

Oh and thanks for the replies l1tech!:driving:

Michael.

 

[scott degroot]

Nice...stay cool