Engine Surges or "Pulses" with A/C AC on- another AC question

[spistols]

I have a 1990 454SS with 116K on it. It runs fine with the AC off, but when it is on, and I am cruising on the highway, it feels like the engine is either surging or pulsing (throttle has small skips). Where should I start looking first to diagnose?

 

[great white]

Short cycling compressor can cause similar conditions.

Check refrigerant pressures high/low....

 

[spistols]

Dumb question, because I am AC ignorant, but what does a short cycling compressor mean?

 

[great white]

In laymans terms: turns on and off a lot.

It results because the compressor runs, pulls the pressure down and the AC disengages when it hits the low pressure switch. the compressor turns off to protect the system. Then the static pressure recovers since the compressor is off and the cycle repeats.

You end up with a load on the engine, then no load, then load, then no load, etc......

 

[dowsewashere]

How bad is this? Mine does it too. Injust tried recharging the system, and the pressure gauge reads up to a point then cuts down. If its short does that mean theres not enough r in the system

 

[dowsewashere]

Actually i just did mine. I dont know of the tbi ac conpressors are different but mine wasnt high enough and kept running and quitting. Topped it off and viola. It works with out the surging issue

 

[great white]

Actually i just did mine. I dont know of the tbi ac conpressors are different but mine wasnt high enough and kept running and quitting. Topped it off and viola. It works with out the surging issue

They are differet but principles of operation are the same.

 

[bluedxj]

good to know mine does this too i thought it was something major. do you have to drain it to fill it up or can you just top it off?

 

[great white]

good to know mine does this too i thought it was something major. do you have to drain it to fill it up or can you just top it off?

You need to know what your high and low side pressure is to know if it's low or if you have something like a clogged orifice valve.

These low side "top off" kits aren't really the proper way to go.

Proper way would be with an ac cart after you've chcked pressures, but that's going to require a trip to the shop.

Thats why these "Walmart specials" are so popular.

20 bucks and you're up and running...if it works right great. If it doesn't you can grenade a compressor.

If the pressure is ok and your orifice is clogged up, the pressure will spike when "topped off" and the high pressure relief will pop and barf pag oil and refrigerant all over the engine bay.



Now, that being said I have used a top up kit myself...but i also had a compressor changed at a shop and they didn't reseat the ball valve properly in low pressure port so i knew it was low...

 

[dowsewashere]

Yeah advanced had artic freeze for two cans and a nozzle was 50$. And it now blows ice out of the vents. So i cant beat it