Bad Contactor

[subzero*psia]

A friend of mine has asked me to come look at his heat pump.

He says it runs in A/C mode but doesn't blow cool air. I am thinking he may not be noticing it as the ambient is already cool and he may not be "sensing" a low temperature difference.

He puts the unit into heat mode from a "no-call" position, into the call for heat and it won't run. He went outside observed the contactor not pulling in, so he manually closed it... it ran for a few moments then out.

At first I thought it may be the low pressure control, but if so it shouldn't let the contactor energize period. It may be low on charge but obviously not low enough to open the LPC. I haven't been out to the site so I am not sure of anything... just going on his word.

Any ideas?

[subzero*psia]

Correction... the contactor "tries" to pull in but is very slow.

[Brian_UK]

Originally posted by subzero*psia
Correction... the contactor "tries" to pull in but is very slow.

Sounds a bit like a control voltage problem.....

[subzero*psia]

NOW he is telling me that it DOESN'T pull in when he tries the A/C... I think it is just a weak contactor coil. It is a 24V contactor so possibly the transformer... have to see I guess.

I should know better... doesn't matter if it is a friend or not... they never tell you the same thing twice and mix it all up anyway.

I DIDN'T WANT TO GO, it is a ways away! LOL!! But it is a friend so.... I am going on my day off.

[Brian_UK]

Originally posted by subzero*psia
.. I am going on my day off.

It WAS your day off Dean

[subzero*psia]

Well, before I went there I started thinking about a system I worked on some time ago... a LONG time ago. I remembered a similar occurance... it was low on charge. So I loaded my R22 and went.

When I got there sure enough the contactor wouldn't pull in no matter what... BUT in the call for heat mode I could hold the contactor in and after about 10 seconds the pressure had built up enough to close the LPC and energize the contactor coil and hold the contacts closed. So I added refrigerant. It wasn't drastically low just enough to not close the LPC.

The service valve on the low side showed sign around the snap ring stop (back-seated position). I added tracer and asked my friend to check it every day or two at the locations I suspected. But I also noticed the reversing valve is stuck in the heat mode... his receiver is badly rusted and he is only feeding part of the outdoor condensing unit... frost build-up in bands around the coil. The unit is nine years old and his neighbors said the folks that owned it before him had lots of service calls on it, ONE JUST BEFORE HE BOUGHT THE PLACE.

I suggested he buy a new outdoor unit and line set, I will install it for him... I can see this unit nickle and diming him to death. AND since he is a friend... no mark-up on the system. He agreed (of course) so I will be making another visit probably this coming weekend now.

QUESTION.... the frost bands on the outdoor unit... it appeared that this circuit was restricted. I chased it back to the distributor, it was the only circuit of the three that was frosted. The other two were cool but not frosted... whats your opinion? I am no expert on heat-pumps... I love refrigeration but I admit I am lacking on the AC and HeatPump side.

[Brian_UK]

Originally posted by subzero*psia
QUESTION.... the frost bands on the outdoor unit... it appeared that this circuit was restricted......

Yes, we've had systems where there have been restrictions due to check valves sticking, cap-lines (distributor) blocking. Some of these blockages have never been clearly resolved. They may have been fixed but....

The feeling sometimes is that sticky fingers have been working on the units in the past, the oil has broken down and is beginning to clog the narrow pipes.

Mind you, it could just be that the gas charge is still low.?.

[frank]

I recently came across this very same problem on a Daikin low wall unit. The installation engineer came back and said that on commissioning he could not get the suction pressure up above 35psig. When I looked closely at the system the indoor coil was only frosting on the lower third of the evaporator and one line out of the distributor was frosting.

When we stripped the coil out and de-brazed the dist'r we found the 2 out of the 3 feeder pipes into the evaporator were blocked, apparantlly by some over zealous factory worker in Belgium! A new one was fitted and the system continues to run like a dream!

Moral of the story is - don't trust it just because it is new!

Frank

[Brian_UK]

Originally posted by frank
Moral of the story is - don't trust it just because it is new!

Oh so true and welcome to the forum Frank