"fmr9" suggested I transfer my post to the A/C forum. So, here goes.

Just converted my '91 F-150 4x4 A/C to R-134. In the process I replaced the compressor, all the hoses (manifold & liquid line), orifice tube and accumulator.
When I accelerate with a/c running in Max, the airflow from the vents stops and doesn't return until a long time after I let up on the gas. However, if the a/c is running in Norm everything is normal.

Temperature from the vents is no colder than 65F, mostly 70-80F.



Anybody have any ideas.
Did I mess up the conversion or have I discovered a vaccuum problem?

Thanks in advance
TX F-150

 

"Did I mess up the conversion or have I discovered a vaccuum problem?"

Probably both.

When the airflow stops coming out your panel vents, it has to go somewhere else. Check the defroster outlet.

As far as the outlet temps go, what are your low and high side pressures?

What do the evaporator inlet and outlet temps look like?

Exactly how much R134a was installed?

Steve

 

Default position in the event of a loss of vacuum for the selection of registers, floor or defost is defrost. Since it is occuring only during acceleration my guess is that you have installed the check valve for the vacuum reservoir backward, or the reservoir line or reservoir itself has a leak. As to the AC discharge temps you need to provide info as Steve stated in his post.

John

 

I have a pressure guage set for the hi and lo pressures. The manual talks 'bout cycle times, do ya'll want those times also?
How do I measure the evaporator temps. Do I need a special thermometer? I assume, the one for vent temps won't work for this.

I have not touched the vacuum system, so my guess is a leak somewhere. As the vacuum issue arose just recently, I don't think A/C work done in a shop many years ago is the cause. Will investigate and let you know.

 

Center vent discharge temp is OK for evaporator temp. Get us the pressure readings and discharge temps at idle and at 2000 RPM. Also get us the outside air temp. Those should be OK to help diagnose the problem. Also what is the R-12 capacity of the system and how much R-134 did you charge the system with?Look around where you worked when you worked on the AC conversion and you might find the vacuum problem. Old vacuum hose is prone to split or crack if you just bump it sometimes.If you have a vacuum gauge get the readings at idle in neutral or park.

John

 

Just wrap your hand around the evaporator lines and feel them. If the system is properly charged, both lines will be very close in temperature, somewhere around 35-45F.

Cycle times become important below around 85-90F, so go ahead and include that along with the ambient temp when the readings and the cycle times are recorded.

Steve

 

During the conversion I used parts and supplies from AutoZone. All parts were labeled for R134a & R12 use.
The lo and hi connectors required adapters to receive R134a-type fittings.
Used Pag46 oil with UV dye to fill the system, and straight Pag46 to lube the o-rings.
Quest brand Re-chill kit with 32 oz. R-134a, 4oz. Subzero synthetic A/C booster kit, packed together in 2 - 18oz. cans.

I also did a UV leak check after the pressure readings. Found minor traces of UV dye near the Lo & Hi fittings. Wiped them off, did not reappear. The rest of lines and fittings didn't show any dye.

Looking at the vacuum system, I didn't see any obviously broken hoses. It appears some of them are wrapped up in electrical? harnesses. [Didn't expect that one]

Here are the requested pressures and temperatures:
outside air temp 78F
Numbers are psig and F with A/C set to Max
Pressure/Temp w/Engine OFF

• Lo 86
• Hi 84
• Vent 90F

After Engine Start 800RPM

• Lo 68
• Hi 110
• Vent 70
• Cycle time (on-off-on) 7seconds

1500-1600 RPM for ~ 8minutes

• Lo 54
• Hi 110
• Vent 75F
• Cycle time (on-off-on) 3 seconds

Engine @ Idle again 800RPM

• Lo 52
• Hi 115
• Vent 75F
• Cycle time - not taken

Engine @ Idle after total run time of 18 minutes

• Lo 48
• Hi 115
• Vent 75F
• Cycle time (on-off-on) 6-7 seconds

Evaporator temps (to the touch)

• orifice side - very cold
• compressor side - warm (ambient)
• the temperature differential is very pronounced

I hope this is the info ya'll were looking for. You have helped a great deal already. Took some digital pictures as well. Couldn't figure out how to include them probably operator error.

 

Your high side pressures are nowhere NEAR being high enough... and your low side pressures are too high..

Almost looks like the compressor is junk.

Why did you convert in the first place?

 

Had taken the truck to an A/C shop for a performance check.
Their answer, I quote "Vehicle A/C pressures not good 85psi on low side 175psi on high side, pressure should be 45psi low & 300psi high.
Vehicle needs A/C compressor, drier, orifice & evac/recharge a/c system. cost of repair $1,000.00 plus tax" end quote.

So I did the work myself and converted it to R134a in the process. Everything is new execept the evaporator core. (see opening post)

 

CORRECTION!
Had taken the truck to an A/C shop for a performance check.
Their answer, I quote "Vehicle A/C pressures not good 85psi on low side 175psi on high side, pressure should be 45psi low & 300psi high.
Vehicle needs A/C compressor, drier, orifice & evac/recharge a/c system. cost of repair $1,000.00 plus tax" end quote.

So I did the work myself and converted it to R134a in the process. Everything is new execept the evaporator core and the condensor. (see opening post)

 

I am having a similar prob on my 91. Except when I put it on max it does not seem that there is any difference. When I accelerate it does go to defrost then returns after RPMs fall below about 1300.

 

If you didn't change the condensor I suspect that your orifice tube may be plugged with junk from the previous compressor. This would cause the suction side to be high but it should also cause the high side to be high as well. But you may be low on charge and that would cause a low high side. You need to flush the condensor, better to replace it, anytime you replace a failing compressor. I would remove and inspect the orifice tube, flush the condensor and lines to and from it and then vacuum and recharge the system and hope that none of the crud got through to the drier. Better bet would be to flush all of the lines, evaporator and condensor, replace the drier, vacuum and recharge. Also, add about 5 ounces of PAG if you flush as I suggested.

John

 

Took the truck to my local indy shop to help chase down the vacuum problem.
The short version of the story is, I have to do the conversion and installation over again.

Here are the details:
It seems when I did it the first time leaks crept in through the fittings and clutch switch. The compressor is leaking at its centerseal. The shop mechanic also suspects either an incorrect orifice tube or it was installed backwards?

For the conversion fittings (R-12 screw-type to R-134a snap-type) the shop says I should have removed the Schrader valve on the high side before attaching the R-134a fitting. Don't remember seeing that on the instructions.

As I have to take the A/C system apart again, I was also advised to check the orifice tube for debris from the condenser [he called it Ford's black death?]

How do I do it right the second time around?
All the parts I bought from AZ, so I think I'm stuck there.
I plan on replacing the condenser, following jtmerritt's suggestion.

Please heeeeeeelp!!!!
I have a long weekend and would like to complete it by Monday.

Thanks ya'll
TX F-150

 

My warranty replacement parts are due today: compressor, condensor, liquid line, orifice tube, accumulator/dryer, high-pressure line, O-ring kit. Only the evaporator core will stay.

What steps can I take to assure that the system is tight?
- During the first install, the connector between the accumulator and high pressure line (~ 1" nut) was hard to get on. Did I cross-thread it?
- Can I use Teflon tape or other sealants on the threads of the connectors to help seal the system?

Is there a particular technique or sequence in which to do the conversion from R-12 to R-134a?

Can anybody help me with this?

Many thanks to all of you who have helped me get to this point. I have learned quite a bit.

TX F-150

 

First flush the evaporator using a cleaner (lacquer thinner will work) and compressed air. I pour the cleaner in and blow it out on to a clean white rag or paper towel and continue to do this until the cleaner comes out clear. Same with any other components or lines you plan to keep. Do not use any thread sealer, only lubed o-rings. Too much chance of the sealer getting into the system. Properly installed o-rings and fittings and you should not have any problems with a leak. Pull a vacuum and if it won't hold and you can't find the problem, you will need to borrow or rent a sniffer. I charge the system with a little freon and then find the leak. Fix the leak, discharge and vacuum and you are all set to charge the system. while assembling and before vacuuming and charging, add an ounce each of PAG to the evaporator and condensor and whatever amount is indicated for the compressor. I put a thermometer at the center discharge vent, blower on high, max AC and start to charge the system. I don't go by the 80% rule since that is often not accurate. I continue to add freon and watch the center discharge temperature to see it drop, once it starts to go back up I stop charging and remove just enough to get back to the lowest temp. I do this with the engine idling at about 1500. I also place a fan in front of the condensor and periodically hose down the condensor. I have done it this way more times than I like to count and have never had a problem. If I have forgotten anything just ask.

John