Hope someone can help me figure this one out:

The rear washer on my 1990 245 will only squirt for about 5-10 seconds then stops. Sometimes it will work again after 15-20 mins sometimes it won't until the next day. Pump is running fine when this happens. Swapped it with the one for the front washers: no change. Replaced the little anti-drainback gizmo in the line back by the tailgate: no change. --Removed this device-- tried it: no change. Removed the nozzle for the rear window: you guessed it: no change. Let things rest a while, whole scenario repeats itself. Can't think of anything else to try except run an entire new hose. HELP!

I remembered once I had the same problem with my Underground service truck , it would squirt water for a little while then stop , and like you said not work for a few days. No real pattern. It did my head in as the saltwater from the mine was constantly spurting onto the windscreen it had to be fixed.(saftey issue).
I inspected , modified , adjusted ,theorized ect ect.
This was a way shorter circuit than your volvo's but I replaced the check valve as you said you have done ( no change ) Blew out the entire length of the fluid line ( no change ) then I replaced the whole fluid line pipe and it worked fine. I am pretty sure that where the fluid line passed under the trim near the passengers feet area was the place over time where people constantly treading on the trim slowly squashed the pipe restricting the flow . Air seemed to pass through but if the diameter is reduced in size I would think that this is where the water has a problem getting through.
( My experience , theory and remedy )

Si850

Have you tried pricking the end of the nozzel with a pin and also running a glass cleaner solution mix through the washer bottle. The check valve you described was a culprit with a blockage situation I had , i replaced it and it worked fine.Like Ken said if the pump motor is cavitating or trying to stall out you have an component problem.

Si850

Lets review the obvious. Are you sure that the pump motor continues to run? There could be a relay or electrical swith/connection that overheats and cuts out the motor. If we are sure the pump motor is running (amp meter to measure draw), then pull the hose at the pump outlet and see if the pump continues to pump with no hose or a new piece of hose. If it quits pumping but the motor is still running then I see two options. (1) The pump impeller starts to slip and does not pump even though the motor is turning. (2) Debris is blocking the lines. Maybe debris in the reservoir is being sucked into the inlet (probably a screen) and blocking the pump. Pumps that are restricted on the supply side usually start cavitation which is very noisy and very bad for pumps in general. You should be able to hear the pump grumble if the blockage is on the suction side. If it works fine with the hose off then something may be blocking the lines from the pump, but I would connect them one piece/fitting at a time and flush them out with the pump or low pressure air. These are the trouble shooting steps that I see. Good Luck.
--
'80 242 DL (20 years, 315k miles, retired); '95 855 GLT, (190k miles, suddenly retired by 16 yr old daughter); '99 V70 XC 105k miles and counting . . .

Thanks for the quick answers guys. To answer a couple of the questions: the pump does continue to run when the flow stops. Also, remember that I swapped the front pump for the rear and I even hooked up the hoses for the rear washer to the front pump and still had the problem. This is why I am stumped. I'll try a short section of hose at the pump to check how it pumps and heck I'm even ready to run another line along the outside of the car to the rear nozzle.

Williston,
Sounds like there is a kink in yor discharge circuit.I had a 245 picked it up for $200.00 au. Solid car . I did a head so I gave it to the mines I was contracting to and they used the jaws of life on it to conduct mines rescue from time to time. Anyway this kink may possibly be where your tailgate hinges off the roof of the wagon.I had no power to my rear windscreen wiper and noticed that the electrical service was kinked and had severed over years of use.This might possibly be the same area where the fluid kink is as I am pretty sure the electrical runs alongside the fluid line.
If that dosent isolate the problem you might possibly have to exchange the whole rear fluid circuit.
Si850

Thanks for the input. I still had the same problem when I disconnect the line at the little anti-drainback valve which is behind the panel near the tailights.
I put the end of the hose in a jar and had my son run the washer. Ran fine for 5-10 seconds then quit. I'm going to run a line all the way back and see what happens.

trial and error will prevail!

Yeah I'm starting to think there is some kind of kink in the hose or maybe a spot where the rubber is getting soft and it collapses under pressure. That's would be strange though since the pump is -pushing- the fluid, not drawing it, except for the short piece between it and the reservoir....