2nd Gen Non-Engine/Transmission a/c questions

[pbell]

I just replace the evaporator and drier and had the system evacuated and recharged. (see post "a/c evaporator change") the a/c man checked for leaks and found nothing. the a/c blew about 35f and it was great. Parked the truck and the next morning no a/c. Now wtf! He did tell me the Hi side pressure was a little high (350) and low pressure was fine (35). I will check my pressures today and see what they are. What are the correct pressures I should be reading with a good system? Also is it necessary to change the orifice line? Where else can I look for leaks and what would be a good way to find them? (soapy water)



I need help or words of encouragement!

 

[DavidC]

You may want to check your high pressure test port. Mine has been leaking since hooking the gauge to it (supposedly a common problem) put a little soapy water in and check for bubbles. There are many places for leaks including around the clutch on the compressor, the trick is finding it. Just ordered a new line from Tenafly $40. 00.



Dave

 

[pbell]

Just ordered a new line from Tenafly $40. 00. Dave

Thanks Dave, I checked every connection that I could see with soapy water and nothing. I even checked the test ports and the switch on the drier. Where is Tenafly and do they have a web site?

My pressures are 40lbs on low side and 100lbs on high side. When the clutch engages, the low side press. drops to almost 0 then climbs up to 40. Clutch disengages and press. climbs to 50. Hope this helps someone with my prob.

 

[DavidC]

I would not wish this on anyone, but it could be the evaporator under the dash. About the only other way to find the leak is with a sniffer or dye and black light. As for tenafly

http://www.trademotion.com/partlocator/index.cfm?siteid=213794



Good luck

Dave

 

[Ramingit]

Sounds Like your low in R134. look for oil/dirt residue on condensor, lines, and compressor tell sign of leak. preasures change due to temp outside. how much freon did you add after replaceing the evap and dryer?

 

[Andy Redmond]

The low pressure switch should engage the compressor clutch when the low side (suction) rises above about 50 psi and should disengage the compressor clutch at about 28 psi or so (this prevents freeze up).



For Texas weather like we've had the last days, 35-40 on the low side is excellent and 350 would be normal on the high side (95 deg. day plus humidity). The closer to 30 ( low high side pressures) and less than 300 (hi side) should yield a better center vent temps. 35-40 deg. is excellent for a dark color truck in this heat.



You will need an ultrasonic leak "sniffer" to find the leak or dye and a uv/black light. My TIF sniffer will supposedly find a 1/2oz. per year leak. You can also have your shop add dye and use a black uv light to find your leak.



You changed the evaporator (inside blower box) or the condensor (in front of radiator)? Accumalator (dryer) was changed, excellent.



Look for leaks at the low psi switch (leaky switch or oring under switch), a leaky core at the high or low psi fittings, shaft seal etc. Also the connections at the firewall for the evap core, the accumalator and at the condensor and compressor. Test the evap core by running on high for a few minutes, shut truck off, remove the blower resistor from the blower box (near blower motor) insert the sniffer into the cavity, if it goes wild you have a leaky evap core likely). Most likely since you changed the evap, your a/c tech would have noticed a large leak if the evap core was bad (wouldn't hold vacuum).



I'm guessing something under the hood.



Your orifice tube is in the metal high side (liquid tube/line) and is not serviceable on the 98 up trucks (must buy the line to get the orifice tube).



I bet your a/c tech blew shop air thru the lines or maybe flushed them, but maybe not since the compressor was not grenaded. If the compressor has worn and deposited a fair amount of metal flakes on the orifice tube it will block the screen and reduce performance.



You can ck. for proper condensor operation by noting good temp differentials between the suction and pressure/liquid ports with a infrared thermometer or a k-thermocouple in your DMM. You can also blow shop air over the coils to improve cooling (heat exchange at idle) if this cools everything down rapidly the condensor might be plugged (bugs, bent fins etc or internally with debris).



Take pressure readings when the compressor clutch is engaged!



Finally, I think since it did so well after recharging, then only to be poorly performing one day later, that you have a leak somewhere.



Hopefully you or your tech find it soon, as you are aware, HFC 134A is only slightly more expensive than sweet crude!



Also when the tech recharges have them under charge by 2-4 oz. for colder air temps inside the cab. say about 30 oz.



Good luck and let us know what you find.

Andy

 

[pbell]

A/C now working

Well I finally got my a/c fixed. I had a hole in a line. It was the line that ran up beside the intercooler from the compressor. The new line has a piece of plastic there to keep this from happening again. I just went ahead and replaced all the lines and schrader valves and now its cold. I am just wondering if the evaporator was leaking at all. How can I check the old one? (Plug one hole and pressure the thing up under water?) Any suggestions?

 

[Andy Redmond]

You might need significant pressure to find a small leak (say 100-150psi). If you attach plugs in the evap be careful. Maybe a radiator shop would have fitted plugs and test it in a tank of water with it aired up.



On your old evap core, look for a greasy spot up in the fin section or along a tube near a fin, this is usually indicitive of a leak (oil leaking out).



Glad you have cold air now that the 100 plus weather has passed for a few days.



Andy

 

[Jakebud]

My truck had a persistent leak in the AC system, such that I was losing a full charge in about 3 weeks time. My dealer was unable to find the leak, and even put in a new evaporator (warranty on a unit replaced 18 months ago). My truck was in the shop at least a half dozen times with this problem. Well, on my last visit, the tech pulled the clutch off the compressor and found the leak. The freon sniffer was unable to find the leak with the clutch on, but found it easily with the clutch off. I haven't seen this as a problem/cure in the forums previously.



SPIKE