A/C Compressor cycling turning on and off - PeachParts Mercedes-Benz Forum

ps2cho · #1 05-22-2013, 08:57 PM

So I have my A/C system back together....
I have 2 cans or 24oz of refrigerant in her and static pressure is ~230psi but the compressor just clicks on, then off again 1 second later. Over and over...

Belt is tight and everything was working prior. All I did was remove compressor to replace manifold seals and replaced condenser.

Any ideas why its doing this?

duxthe1 · #2 05-22-2013, 09:49 PM

3 Lbs seems like a bit much but I haven't charged a 124 lately and don't know the spec off hand. Cycling on and off though is a typical overpressure scenario. There are no normal operating conditions where it should do that. Static pressure is useless info, though it seems quite high. Need high and low side pressures to figure out what its doing.

EDIT: just noticed it is 2 can OR 24oz, not 2 cans OF 24 oz.

1.5 LBS seemss closer to right but it still sounds like an overpressure, possible high side restriction.

ps2cho · #3 05-22-2013, 10:11 PM

2x12oz cans for 24oz total.

I watched the high side pressures and it was not rising above the 220-230psi.
It also started doing the cycling about 1/2 way through the first can at around 120psi.

I can't give high and low since it wont engage long enough.

I am wondering if the speed sensor went kaput after the removal. Its the first time its been off the car.

ps2cho · #4 05-22-2013, 10:48 PM

You know what, I think somethings blocked.

I rehooked my gauges to the low side (I was using a separate charger hooked up to my can) and the low side is showing 25psi with the compressor off.

THEN, I shut everything down and the high side is reading 150psi and the low side 70psi and I hear gurgling/bubbling noises coming from the condenser line.

Could there be a blockage or something?

ps2cho · #5 05-22-2013, 10:49 PM

You know what, I think somethings blocked.

I rehooked my gauges to the low side (I was using a separate charger hooked up to my can) and the low side is showing 25psi with the compressor off.

THEN, I shut everything down and the high side is reading 150psi and the low side 70psi and I hear gurgling/bubbling noises coming from the condenser line.

Could there be a blockage or something?

lsmalley · #6 05-22-2013, 11:32 PM

possible air introducedd into the system? Try the simple approach first, re-evacuate system and rechargeuntil the compressor stays on (only if it is slightly below or at the recommended amount of freon) and then stop. I don't think if its slightly below the recommended amount you will have a problem, but if it is over, you may have a problem.

duxthe1 · #7 05-23-2013, 12:37 AM

Speed sensor will shut it off and keep it off until you cycle the key. It wont cycle it on and off. Too high pressure in the high side is the only thing I've seen cause a rapid on off cycling. Sometimes you can find a restriction in the high side by feeling for a cold spot in the lines and or looking for frost. A partial blockage can act like an expansion valve allowing the downstream side to get cold when it should be hot.

ps2cho · #8 05-23-2013, 10:43 AM

Gotcha. I will inspect the expansion valve and condenser for blockage.

ps2cho · #9 05-29-2013, 09:59 PM

I flushed the condenser, evaporator and expansion valve again...put it back together charged it and same issue.

When I watch the gauges, the high side is ~200psi and the low side is 10psi, it creeps up to ~25psi, and that is when the compressor kicks on, and it shoots straight down to 10psi again, compressor shuts off....then it takes a good 5 seconds to get back up to ~25psi and the process repeats.

It seems like the compressor shuts itself off when the low side drops (aka as soon as the compressor turns on)...Its not undercharged since BEFORE the compressor kicks on at ~8oz and stays on while more 134a gets sucked in.

Where else could a blockage be or any other ideas? The compressor itself? Drier?

lorainfurniture · #10 05-29-2013, 10:17 PM

Check your connections at the condenser. Maybe you kinked a line? Sounds like classic clogged expansion valve but if it all flushed well then I would be looking for some twisted metal.

ps2cho · #11 05-29-2013, 10:32 PM

Ok its definitely a blockage...

I swapped the drier, no change. So I then jumped the pressure switch and sure enough it went straight into a vacuum on the low side.

I checked condenser output lines and no kinks or anything. Is there a specific way to find where a blockage could be without just throwing parts at it? (I did flush the expansion valve, but maybe I should get another JUST in case whatever is lodged in there is jammed in good and the carb cleaner didn't get it out).

duxthe1 · #12 05-29-2013, 11:11 PM

At this point I'd put another exp. valve in it. That's what the compressor is sucking against.

compu_85 · #13 05-29-2013, 11:18 PM

If you jump the switch what do the pressures go up to? You'll know if the high side or tx vlave has a problem, the high side will shoot up to 300+ psi in a hurry.

-J

hookedon210s · #14 05-29-2013, 11:36 PM

Not recommended to flush the expansion valve---you definitely need to replace it. Mark

ps2cho · #15 05-29-2013, 11:45 PM

Quote:

Originally Posted by compu_85

If you jump the switch what do the pressures go up to? You'll know if the high side or tx vlave has a problem, the high side will shoot up to 300+ psi in a hurry.

-J

Well I only had about ~15oz in and it was 200psi. I didn't see a need to fully charge and stress the system. I just put enough in so that the compressor could turn on. The fact that its going into vacuum was all I needed to know.

I have ordered a new expansion valve and will report back (hopefully saturday) as soon as it is in. Fingers crossed.

Its supposed to 105F starting this weekend, so I need this done ASAP!!!