AC questions

[fordman]

check your expansion valve. that is what my truck was doing. i ended up when i was putting it on. to clean the junk out of it. but i didnt fully clean it. i got in a hurry. i had to tap on it to get it to start moving properly. it also doesnt get as cold as it did with the good expansion valve on it. i wish i hadnt been in such a hurry. but stuff happens and then summer got here in just one day. and i had to have a/c that day.

[basketcase0302]

Bill,

Craig's on the right track about your TXV possibly sticking, the diaphragms are bad about doing this. And like he said also, with it running tap on the TXV valve body and diaphragm in an effort to get it to fully open, (but not with a BFH) LOL! If your pressures are right at idle speed it does sound like a restriction on the low side, (hence the too low of pressure there) which should be the TXV or could possibly be the suction valve in your compressor? Look for a frost pattern up to the TXV that could indicate it's not opening all the way, (in other words it should be colder on the evaporator side when measured with a digital infrared thermometer, (which BTW is one of any A/C guys best friend). Our old York compressors didn't have a high side cut-out only a low side cut-out from the factory I believe to protect the compressor.
Hope it helps! The heat index here this week will be over 100 (was in the upper 100's last week. I'm working outside so I know how brutal it is...

[70_F100]

No high-pressure or low-pressure protection on these systems.

The thermostatic switch cuts the compressor off when the temperature of the evaporator gets low enough, which I think is in the 40-degree range.

[fireguywtc]

Thanks all for the help!

Let me guess, the expansion valve is the thing I just wrapped up in tar tape? It is in line on the top of the evaporator? I will have a hard time giving a good wack then. It is difficult to tell if it is doing what it is supposed to. If the thermostatic switch is the only regulation for the compressor and it is set for 40, then it will likely never swtich off in my case. What else do I need to do to maintain the correct pressure? Or is that what the expansion valve is supposed to do, hold back and regulate the pressure?

[fordman]

dont whack it. lightly tap on it. or wrap a warm rag around it.

[fireguywtc]

How will I know its working?

[fordman]

it will get colder. unless 70f100 is right and it needs a temp switch thing. he may be right. i am not a a/c pro at all.

[basketcase0302]

fireguywtc on Tue Jul 19, 2011 7:03 pm
How will I know its working?

Here's where an infrared digital thermometer will be your best friend.
Point it at the evap coil (or suction line) that attaches to the coil in the cab. When your tapping you should see a difference in the line temperature (colder) if it's sticking.

[fireguywtc]

Interesting. I don't have one of those but I do have access to a thermal imager. I am going to give it a try with that.

[70_F100]

fireguywtc on Tue Jul 19, 2011 7:03 pm
How will I know its working?

Here's where an infrared digital thermometer will be your best friend.
Point it at the evap coil (or suction line) that attaches to the coil in the cab. When your tapping you should see a difference in the line temperature (colder) if it's sticking.

You should also see a change in the suction pressure, which would be nearly instantaneous, as opposed to checking temps which will be a little slower.

I have not really had good cooling since I had to switch over to R134a a few years ago. Then, last summer, I went to replace the receiver-drier and of course the threads on the aluminum fitting on the condenser stuck to the steel threads in the fitting as I was removing the liquid line at the condenser. Couldn't find a good used condenser, so I bought one of the serpentine replacement condensers. Haven't been able to get the temps below about 55 degrees since that debaucle. Replaced the expansion valve, no change. Tried a second condenser, no change. Flushed everyting, no change. Replaced compressor, no change.

Pressures are good at idle, low side drops when you rev the engine, just like there's an obstruction in the system, but I can't find anything.

I'm hoping you find the problem, because I'm tired of throwing money at mine!!

[fordman]

someone on here said to replace the condensor with a larger one if using the newer 134A gas. i have not made this conversion to my stuff yet.

[fireguywtc]

Okay, I tried the tapping thing while watching with a thermal imager. Just fyi it had a temp guage on it, but it didn't seem accurate. It didn't get any colder then before, it all seemed the same when I ran it while tapping on the diaphragm. Driving down the road it will only cool off some, but no lower then 60 with outside ambient temps in the high 90's. It will cool off a bit more to near 55 when not moving/idling.

The thermal imager did show everything appears to be working the way it should. Evaporator got colder, condenser hotter, and appropriate lines turned hotter and colder.

Perhaps I should just be happy with the way it is for now, it does cool off, just not as much as though it would. btw fordman, I did get a newer, bigger condernser when I fixed my AC system.

[70_F100]

I did get a newer, bigger condernser when I fixed my AC system.

What kind of condenser did you use?

[fireguywtc]

I don't know what kind it is or what it went to, I think it was for a ford though. The local radiator shop sold it to me when I found out it wasn't worth using the old one. My old one was still air tight, but the fins between the tubes was coming apart.

It is not too much bigger, but it is wider and taller. It covers up the entire hole in front of the radiator. Plus it has alot more tubes with the round tubes at the ends. It was brand new when I got it and we adapted on there. Thought it was better to pay $75 for a new bigger one to adapt rather then $250-$300 for a new factory replacement. I can try and get a pic if anyone is intersted.

[fordman]

i dont want to derail this thread. but i wonder if there are some sort of charts for sizing condensors for our systems or other systems.

ok now back to the show. when my factory air was working. it cooled. but you could still feel the heat from the enigne in the cab.