MD2 Won't stay out of defrost

[referwrench]

I cant' get MD2 to stay out of defrost. The unit cools down to temp. but after defrost cycle, when it tries to cancel, the diesel eng. almost quits, then unit goes back into defrost and runs fine until defrost tries to cancel again. This continues over and over until I pull out the relay.
I've changed : def.term sw., high temp. sw.,put in a used timer/relay circuit board and disconnected air sw.
Please help
Thanks

[cadwaladr]

Suction regulator problem

[referwrench]

it seems like it's electrical. the defrost relay, pilot solenoid, and damper door solenoid all pull in. It's like a normal defrost cycle, except it tries to cancel but it keeps starting.

[cadwaladr]

What happens if you put it on a heat cycle ie set the temp high does the engine labor?

[IRMechanik]

I'm with Cad, sounds like a cpr problem or maybe head pressure spiking coming out of defrost.
What's pressures running?
When it almost dies does it sound like it bogging down or is the fuel solenoid dropping out?

If it's an MD-II (R-12) the cpr should be 24-26 psi
If it's an MD-II Max (R-502) the cpr should be 19-21 psi

[pkw111]

try it on standby, will probably trip the motor. And as above posts will be the cpr valve.

[referwrench]

no, it only labors when it tries to get out of defrost

[referwrench]

I didn't check pressures because I assumed elec. Why would the cpr cause the relays and solenoids to pull in.
Cooling and heat work just fine.
I'll check pressures and make sure if the fuel solenoid drops out or it labors but I'm pretty sure it drops out.

[cadwaladr]

The regulator takes the load off the compressor/engine while it's defrosting the back pressure is high when it's on a defrost cycle,if the valve is faulty misadjusted would give the symptoms you describe

[IRMechanik]

I didn't check pressures because I assumed elec. Why would the cpr cause the relays and solenoids to pull in.
Cooling and heat work just fine.
I'll check pressures and make sure if the fuel solenoid drops out or it labors but I'm pretty sure it drops out.

I'm still thinking cpr, high suction pressure=high discharge pressure and tripping the high pressure cutout.

[aircon50]

Sounds as if there are two problems.
1. If unit tries to re-initiate defrost as soon as terminated this points to an electrical problem. Ok, recheck the defrost circuit. ETS must be opening to allow termination. Does the defrost relay de-energise? Even if the air switch, manual defrost or remote manual defrost switch (if fitted) were closed, the defrost would cycle on ETS opening and then re-closing. For example - MD-II with TG-V the ETS opens at 11ºC and closes at 6ºC.
2. I have had similar in the past. Definitely check SPR setting. Settings are slightly different for the refrigerant and thermostat options, but in any event should not exceed 1.45Bar (21psig). Engine and electric motor overload will result.
Good luck, Graham

[djbe]

If the cpr is at fault usually you can tell if you loosen the cap for the adjuster, if gas leaks out there you go. If you unscrew the cap completely expect it to be blown away and total refrigerant loss.

[referwrench]

Truck had to go back into service without defrost. Had to use it.
I checked the cpr pressure, was 90 psi. The next chance I get I will put one in. The ETS is working fine.
I'll be back with an update.
Thanks to all for your help.