m.colley

Anyone ever had a AC compressor when energized almost bog a running car done so far that that the car stalled? Any suggestions?


Martin

ezone

IF the clutch relay is stuck on and keeps the compressor clutch engaged when it shouldn't be on, the high head pressure can bog the engine pretty hard (fans do not run when the clutch relay sticks on).

Overcharge can act the same, due to high head pressure.
If the fans quit, the same thing can happen--high head pressure.



If high side pressure gets high enough (470-500 ish PSI?), the system will vent excess pressure through the safety relief valve (burp out a cloud of freon).
IF the safety valve vents, it is supposed to be replaced as it is no longer sure to open at the correct pressure. If it vents, there is usually be a large oil stain nearby.


HTH

m.colley

Thanks for the heads up on a few things to check and observe. You even answered a few questions I hadn't asked yet.

After replacing the compressor clutch and field coil over the weekend I noticed a couple of odd things. Occasionally both condensor and radiator fans would occasionally cut out/quit working when the compressor engaged. I also noticed that occasionally the car would idle way down to an almost stall when the compressor would engage. Then as you said it even burped once and I recognized the smell of refrigerant.

I hooked up my gauges (low side only) and was first puzzled because at 90 degree ambient I was only showing about a 38psi discharge pressure which would be low on charge. I'm thinking now that the TXV is not opening correctly, but I'll have to wait til tomorrow to verify as I need to get a high side adapter so I can see what my gauges tell me. The burping seriously sounds like a restriction causing high head pressure and thus the burping.

Thanks again,
Martin

ezone

Why was the last compressor replaced?

m.colley

I didn't replace the entire compressor, just the compressor clutch and field coil. I replaced those parts due to clutch engaging erratically and then not at all and noise. The clutch relay has been replaced as well.

When the ole lady first told me that it was acting up ( its her daily driver) I assumed it was her imagination as we had just started having our first real heat wave. The first week of June we took it on a trip to TN and it was still acting up ( I was driving ), so I saw what she meant. Another week later I finally got around to looking at it and diagnosing it. The clutch relay was the first thing replaced, followed by the compressor clutch and field coil this past weekend.



Martin

m.colley

Some more details.
After reading ezone's reply to my question I paid attention to a few things on my way to work this morning. I noticed that even though all the switches were off on the AC panel I had cool air coming thru the vents as long as the car was moving, same thing happened on the way home even though it was over 90 degrees outside. This told me the compressor had to be running even if slowly or it wouldn't be pumping gas and removing heat from inside the car.

After I got home I did a little more investigating and found that the new relay I installed was sticking and was energizing the compressor clutch regardless if the fans were on (condensor) or if any switches were (ac/max ac) etc on. I swapped a relay around to prove what I thought. They twin fans came on, the compressor clutch energized and the car began running somewhat normal again. The car no longer bogged down like what was originally happening.I was smiling.

Now here's the new issue.
With the car running I hooked up my gauges and the system was low on charge which was to be somewhat expected since the car had burped several times. At 90-92 degrees outside it was running around a 28-32 psi suction and if I remember right around a 150 head pressure. In an attempt to get the suction up in the 50-55 psi range (90 degree range) I started adding some R134A a little at a time giving it time to settle down in between bursts of refrigerant. I never could get the suction up in the range I was targeting, even though the head (high pressure) side did climb.
When I stopped the suction was in the 34 psi range and the high side was in the 200 psi range.

Am I right in thinking that the TXV is not operating correctly since my suction won't increase but my head will??

Martin

ezone

You're expecting too much from the low side, 34-200 sounds fine as is if it is cooling ok.
This isn't a 3 ton R22 unit LOL.


You can't really use the temps on your gauge set with an MVAC system as the pressures can vary widely given different system and ambient conditions.

We've got variable compressor speeds, variable condenser cooling (wind speed), a freekin huge load on the evaporator core at times, the TXV in this car is not a fixed orifice, and the system will never ever freeze up if the freon gets low.




Copied from another post I made a few days ago:

Easy way would be to add a little freon, wait a bit let it stabilize, check pressures on both high and low sides, vent temperatures (and I also feel pipe temps if doing it this way).
Add a little more, check pressures and temps.
Repeat until it's cooling good.
Make sure pressures aren't too high.

System freon capacity is small....A couple ounces over or under spec and performance can suffer.
It's way too easy to put in too much, and performance suffers greatly if it's over or under charged.

The pressures are a huge variable, you would almost need to check pressure-temp charts to see if yours is reaching an expected range based on actual conditions.


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Get the car out of direct sun. The Civic system is small and really is undersized for the car, direct sun can overpower the system (add heat faster than the AC can remove it) especially if the car is a dark color, and newer cars are worse. LOL

I can check temps two ways.....
Performance test:
Open all doors and windows, turn AC on and use throttle prop to keep engine @1500 RPM....run for 10 minutes to stabilize the AC system, put fast acting digital thermometers in the center vents and blower intake (open the glovebox wide to find it by the cabin filters)...max AC, recirc on, fan full blast...

Looking for about a 20 degree F or greater drop between blower air inlet and dash vent temps, and this temp difference can vary a lot depending on humidity levels. (High humidity means less drop, low humidity means more temp drop.)

Example
If it's 85* ambient and 60% humidity, test set up as above
got 80* at the blower intake
60* from the vents or less
30 psi low side (20-30 range)
200 psi high side (190-250 range)
that's within reason.


Then roll up windows and seal up the cabin and see what the dash vent temps do. If they drop a lot you're doin good.
If it gets cold enough to have the compressor cycling on-off-on-off it's real good.
If it's real hot out it may not be strong enough to cycle sitting still, but may cycle while driving at highway speed.
I like my digital thermometer to be sensitive and fast enough to watch the temps go up and down a few degrees as the compressor cycles on and off.