AC Assistance Please, Only cool at speed.

[GCroyle]

RVTRKN,



Any chance that you could put together a basic flow chart geared at the DIY to help diagnosis the problem. I'm not thinking of showing a DIY how to do jobs that require opening the system up, that takes special equipment.



If I have a pencil thermometer, infra red thermometer, and either a low pressure gage or a hi low combo gage and your flow chart, this might help us be more self sufficient on low level repairs or learn enough from our diagnostics with a chart like this to know when to cry uncle.



I'm about ready to buy my own hi low combo, I'm wasting a lot of TDR time on these what if's that ain't panning out.



Thanks,



Gary

 

[RVTRKN]

Sorry, I will post it tonight. Reg AC is a little different, but the basic rules do apply. You will need a set of gages (Hi and Low) to see what's going on. If you do your own work its worth the cost.

 

[jelag]

Gary

Harbor Freight has a gauge set for around $30 on sale right now on their web sight and I'm sure its not much more in the store... . I'd loan you my high end set but the freight to/from would be more than the $30 at Harbor...

 

[Crunch]

A while back we charged my brother's pony truck and he brought along his gauges from Harbor Freight. If I remember correctly, they did come with adapters for R134a high and low, but you will need your own bottle to collect the evacuated refrigerant, and the little bottles of R134a you buy at the auto part store or Walmart won't fit the gauge set and there definitely wasn't an adapter for that.

 

[rscurtis]

One thing you may want to check, which I should have pointed out earlier, is to determine that if the truck cools OK at speed, whether this cooling is a function of compressor speed or air speed. You may want to see if it cools with the truck stationary with the engine running at fast idle, or if it cools better with the engine idling and some assistance provided to the condenser in the form of an auxiliary fan or cooling water.

 

[GCroyle]

Jim,



I'm looking at two different mfgr's gage sets right now, thanks for the loan offer. Why don't you get on the Wing and motor em on over, we'll figger it out together.



Crunch,



Collecting evacuated refrigerant, got to read up on that, don't know what that is. I need to get on the gage mfgr's websites and read up on the features and benefits.



rscrutis,



I did put a box fan in front of it one day, but I don't remember any of the results right now. Sounds like a good try w/gages in place.



HHhuntitall,



I did do a soap and water wash of the front end, got some bugs off fer sure and some road film.



Thanks guys.



Bout time to you know what or get off of the pot re: GAGES!

 

[Crunch]

Collecting evacuated refrigerant, got to read up on that, don't know what that is. I need to get on the gage mfgr's websites and read up on the features and benefits.

It means that if you want to pull out the refrigerant that is in your system you will need some kind of a tank, plumbed into the gauge set,to put it in. And if you need to charge your system you will need to use refrigerant in a tank that fits whatever system you are using. I don't think you can pull it out of your AC system and reuse the same refrigerant. So if you buy the little cans to recharge your system you will need an adapter to hook up to the gauge set, use another source of refrigerant that is made to work with the gauges, or use another dispenser that fits the little cans.

 

[jtwcummins]

A gauge set has 3 hoses. One for high side, one for low side and the third for connecting to a recovery/charge machine. The full charge is 1. 87 lbs, but alot come from the factory slightly undercharged. To do it right you need to get an a/c shop to remove the refrigerant and pump system to a vac. and hold it to see if there are any leaks. If it holds a vac then charge system to 2lbs, that's . 13 lbs more than spec but not enough to even begin to give overcharge issues.



To see if it's an airflow problem put gauges on and run a/c in recirc with fan on high and max cool on temp slide. Watch gauges and then put box fan against condenser and run on high. You should see pressures come down slightly. If it's an airflow issue the high & low side pressues will both be high and will drop with more flow from box fan.



The fact that it cools a hiway speeds and not at low in town stop & go points to a bad fan clutch. If you want to clean the bugs/dirt from the fins the best way is pull the radiator and, with engine side up, use soap and a garden hose, NOT a pressure washer, and clean until gunk is gone. Then do the intercooler and condenser from under the hood out. Trying to clean from the front with everything installed can make a slight plugging problem a big one. You are forcing everything toward the rad and can really plug it up.

 

[RVTRKN]

I promised I would post the basic rules, I could not find my papers from school 11 years ago.



DIYers have another way, and it would be to open both HI and LO to the atmosphere and let it out until 1 PSI is left in the system to prevent air from entering. Then charge the factory amount back into it with a scale that measures ounces. This is a quick way to determine refrigerant charge is proper, before moving on to other things. Pressure wash the condenser but make sure you don't crush the fins with the high pressure, I do this all the time to rooftop AC units. With the engine at idle it should cycle from the low pressure switch just above the freezing (pressure/temperature relationship). There are specs for the air temperature at a specific RPM. Cab temperature will effect this, meaning the warmer the Cab the higher the refrigerant pressure will be. When I did my 94 gasser I got the info from the shop manual and determined it was low on refrigerant and found the leak in the Evaporator :{

 

[jelag]

Gary

Do you want me to send you a vacuum pump and my gauge set... . I have both at the house...

I've always pumped them into a vacuum and than let the system set with the pump connected for 2-3 hours... to allow any water in the receiver dryer to boil off... I than shut the gauge set and let it sit for a couple of hours to be sure that there isn't any leaks... the optional method would be to charge the system with nitrogen to 200 psi and let it sit for 30 min, and check for a gauge change...

And than recharge it... .

 

[RVTRKN]

Nitrogen is the better method, 100 PSI though, its just difficult for a DIY. When you pull a vacuum with a leak, it will pull moisture into the system and contaminate the dryer. If that happens, pull it into a vacuum after the leak is repaired and place a drop light onto the accumulator so it will heat it up to help boil off any moisture.



As I described in last post, don't let the pressure go below atmospheric pressure (1-2 PSI) and then charge it with the proper amount. This helps in two ways, you don't need a vacuum pump and the problem is fixed short term, if it works, and if it didn't, you didn't waist a lot of time and move on to the next step.

 

[GCroyle]

Jim,

RVTRKN,

JTW,



You guys are coming up with help and ideas faster than I can try them. I can't work on it till this weekend and I'm planning on gages before any more guessing by me and all of your best efforts.



I'm gonna start with some of the air flow tests described and I'll check the airflow with an additional technique sometime when it gest dark outside.



Thanks guys.

 

[GCroyle]

Gage set is in the house!



Stopped and bought a hi/lo gage set, hoses, quick connects w/valves at the QC.



I experimented on the '97 tonight, had to review directions, open this valve, close this valve etc. a few times, added a smidgen more and VOILA! Jake got in the truck, big smile on face!



Sorry, didn't have time to get them on the '05 yet, this weekend.



Gary

 

[RVTRKN]

Gary, how did it go?

 

[GCroyle]

Gage Report

Ambient 84 DEG, High Humidity, engine idling, A/C on RECIRC, Thermometer in drivers side center vent.



The readings (PSI) rhythmically fluctuation from 27/225 to 50/325 syncronized to the fan ramping up to HIGH when the pressures get up there and then the fan slows down when the pressures drop, pressure goes up fan kicks in and this oscillation repeats. Center vent 60 DEG. Since I didn't have a fixed value, I only added a sniff or two as a test, it did seem to help, but when you slow down, it warms up. Today I ran it at 70 MPH mid 80's lower humidity and it would get to 40 ish at the same center vent. Engine temp on 6 Gun PDA 192 DEG.



I tried a box fan in front of the truck, no real change observed, but you can feel air moving across the system quite easily.



Questions:



Any ideas?

Any flashes for related to this?

General question, is the temp controlled by blending cool and warm air or cycling the system?

 

[icman95]

You said you added a sniff or two as a test and it seemed to help a bit. Perhaps there is a leak in the system large enough to let the added refrigerant leak out rather quickly so that it helped for a short time, until it leaked out.

 

[RVTRKN]

Seems to be running higher than normal on the high side, estimated pressure for 85* ambient temp should be around 160 PSI.

85*

+ 30* over ambient

---------

115* total converted to pressure for temperature/pressure relationship 160 PSI



Rule of thumb is to add thirty degrees to the ambient temperature and that should be your pressure you should have on the high side, for the temperature/pressure relationship.



The temperature/pressure chart for R134a should be on the gage set you bought, you will see the pressure ring and then three different refrigerant temperature rings. When the needle is on the pressure value follow the needle down and when it crosses the 134a ring, that is the temperature value for that pressure for 134a. 225 PSI seems high at idle. Have you looked up the manual for any specs, or the proper sequence of operation pertaining to pressure at idle, for your MY CTD. I would look it up, but I gave my 04 manual to my brother when he bought my 04. 5 CTD.



I would pressure wash your condenser with a mild detergent taking care not to crush the fins. Make sure you rinse it good, let dry then try again and see what the pressures are.



Your low side will cycle on specific pressures, that should be noted in the manual. The actual numbers you reported, off/open at 27 PSI (32*) and on/closed at 50 PSI (54*)



Note that the temperature is just above freezing on the low side at 27 PSI for R134a, you dont want to freeze the evaportator, and the pressure set point should open the circuit just above that pressure which it looks like your OK there.